Atomic Structure.

Atomic Structure

Matter Consists of Particles
Democritus Aristotle Aristotle, Democritus When: More than 2000 years ago Where: Greece What: Aristotle believed in 4 elements: Earth, Air, Fire, and Water. Democritus believed that matter was made of small particles he named “atoms”. Why: Aristotle and Democritus used observation and inference to explain the existence of everything. Aristotle Disagreed with Democritus and his ideas about atoms because how are these particles all held together? Democritus could not answer. 17-18th Centuries

John Dalton 1803 I am a genius! Atomic Theory of Matter based
on the following postulates: 1) Each element is composed of particles called atoms. 2) All atoms of a given element are identical. 3) Atoms are neither created nor destroyed in any chemical reaction. 4) A given compound always has the same relative numbers and kinds of atoms. Who: John Dalton When: 1808 Where: England What: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom. Why: Building on the ideas of Democritus in ancient Greece. English Schoolteacher- Atomic theory of matter, Observations and readings- conclusions properties of matter could be explained in terms of atoms. Small but important exceptions to some of Dalton’s postulates however still basis for our understanding of chemistry today. See atoms- Scanning tunneling microscope- blurred picture, little detail about what atoms look like inside. THEORY= logical time tested explanation POSTULATE=demand.CLAIM

What is an atom? Smallest particle of an element that retains the properties of that element Gold Atom Model the world’s most powerful transmission electron microscope — capable of producing images with half-angstrom resolution (half a ten-billionth of a meter), less than the diameter of a single hydrogen atom also known as really freaking small Dalton & Contemporaries thought atoms were hard & round, much like extremely tiny marbles or ball bearings.

JJ Thompson (1897) Used a cathode ray tube and found negatively charged particles Discovered electrons (e) Plum pudding model Could not determine the mass Won Nobel prize. Thompson created a tube that had a positively charged anode on one side and a negatively charged cathode on the other side. Removed gas to create vacuum, then added gas, then turn on electricity to create stream. Turn electricity on plates and stream bent toward positive plate. Also, spun a paddle wheel so knew particles were hitting it making it spin. Thompson then applied a magnet to the middle of the tube and discovered that negatively charged particles were emanating towards the positive magnetic field. From this, Thompson concluded that negatively charged particles, called electrons, were present in atoms. Lates 1800’s Watched the deflection of charges in a cathode ray tube and put forth the idea that atoms were composed of + and – charges. The negative charges were called electrons, and thomson guessed that they were sprinkled throughout the positively charged atom like choc chips sprinkled throughout a blob of cookie dough. Thomson knew the rays must have come from the atoms of the cathode because most of the atoms in the air had been pumped out of the tube. Because the cathode ray came from negatively charged cathode , thomson reasoned that the ray was negatively charged. DEMO- TV- MAGNETS

Robert Millikan (1909) Oil drop experiment Measured charge of electron
Calculated mass of electron Mass = 9 x grams or…. 1/2000 mass of H atom How to prove something is a particle? Measure it’s mass. Mass is a fundamental property of matter. American Physicist- Univ. of Chicago, succeeded in measuring the charge of an electron Aimed x rays at droplets so would gain a charge and by changing the electric field between plates he could suspend the oil droplet. He knew the mass of the droplet and how much charge in the electric field and could determine the charge on each dropletalways a multiple of -1 What Millikan did was to put a charge on a tiny drop of oil, and measure how strong an applied electric field had to be in order to stop the oil drop from falling. Since he was able to work out the mass of the oil drop, and he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have. By varying the charge on different drops, he noticed that the charge was always a multiple of -1.6 x C, the charge on a single electron. This meant that it was electrons carrying this unit charge. Next, Millikan applied a charge to the falling drops by illuminating the bottom chamber with x-rays. This caused the air to become ionized, and electrons to attach themselves to the oil drops. By attaching a battery to the plates above and below this bottom chamber, he was able to apply an electric voltage. The electric field produced in the bottom chamber by this voltage would act on the charged oil drops; if the voltage was just right, the electromagnetic force would just balance the force of gravity on a drop, and the drop would hang suspended in mid-air. Now you try it. Click here to open a simulation of Millikan's chamber. First, allow the drops to fall. Notice how they accelerate at first, due to gravity. But quickly, air resistance causes them to reach terminal velocity. Now focus on a single falling drop, and adjust the electric field upwards until the drop remains suspended in mid-air. At that instant, for that drop, the electric force on it exactly equals the force of gravity on it. Some drops have more electrons than others, so will require a higher voltage to stop Measured charge of electron by examining the behavior of charged oil drops in an electric field. Charge of single electron= 1.60 x 10-19coulombs C= coulomb= SI unit of electrical charge Mass of single electron= 9.11 x 10 –28g Mass of Neutron= x 10^ -24 g Video- 29 minutes long--- Mechanical Universe

Gold Foil Experiment Radioactive sample (Po) emits alpha particles (+) most went straight through-few deflected at large angles and bounced backhitting dense and positively charged area. Also, new it was a small area because only a small portion bounced back. What was it hitting? THE NUCLEUS! ~1/8000 deflected- most particles were undeflected. Expected min. deflection. Some completely reversed direction. 2 years to think about it. JJ thompson. Plum Pudding model- neg charges are distributed evenly throughout an atom’s positivelt charged interior. Rutherford- proposed that all of an atom’s positive charges, as well as most of it’s mass, is concentrated at the atoms’s center= nucleus.

Ernest Rutherford (1909) Discovered:
1. nucleus is positively charged, very dense, & very small (1/10,000 of diameter) 2. electrons are in space surrounding nucleus 3. most of atom is empty space Thompson discovered electrons but atoms are neutral so there must be a positive charge. Where are they? Alpha particles are +2 charge (beta -1) learned this from radioactivity experiments in which he placed a radioactive sample in front of a electrically charged plate. Beta attracted to + plate and alpha attracted to – plate. Gold foil: threw some alphas at gold foil and saw that some were deflected….meaning some of those positive alphas hit the positive proton in the nucleus and scattered. About 1 in 8000 were deflected. Plum pudding was wrong! Atom to scale: place a dime in the center of a football field and there is your nucleus. The electrons are about the size of Roosevelt’s eye in the portrait.

What does this mean? is now replaced with Rutherford’s model.
Atom analogy: nucleus is a fly in the center of Yankee Stadium and the electron cloud is the rest of the stadium Thompson’s Plum Pudding model

•Believed universe made of 4 elements: earth, air, fire, and water
Scientists Recap Aristotle Democritus Dalton Thompson Millikan Rutherford •Believed universe made of 4 elements: earth, air, fire, and water •Believed matter made of particles he called atoms •Atomic Theory of Matter •Discovered electrons using cathode ray tube •Plum pudding model •Oil drop experiment Atomic Theory postulates: 1) Each element is composed of particles called atoms. 2) All atoms of a given element are identical. 3) Atoms are neither created nor destroyed in any chemical reaction. 4) A given compound always has the same relative numbers and kinds of atoms. •Measured mass and charge of electron •Gold foil experiment •Nucleus positive and dense •Electrons in space surrounding nucleus

Modern Atomic Theory Electrons (e) occupy “cloud” outside of nucleus
They DO NOT orbit around the nucleus like the planets do around the sun… Impossible to know where an electron is at any given time

Old vs. New Electron Cloud Orbit Proton = nucleus
Cloud is a region where you are more likely to find an electron

Protons (P) Proton +1 charge
Mass: x g (almost mass of H atom) or 1 amu Location: nucleus

Neutron (N) No charge = 0 Mass = 1.675 x 10-23 g or 1 amu
Location: nucleus Discovered by Chadwick (1932) Neutron is slightly heavier than proton (1.675 vs x grams) Nucleus heavier than expected so knew there was another particle. For four years, James Chadwick was a prisoner of war in Germany. When World War I ended, he returned to his native England to rejoin the mentor of his undergraduate days, Ernest Rutherford. Now head of Cambridge University's nuclear physics lab, Rutherford oversaw Chadwick's PhD in 1921 and then made him assistant director of the lab. Chadwick's own research focused on radioactivity. In 1919 Rutherford had discovered the proton, a positively charged particle within the atom's nucleus. But they and other researchers were finding that the proton did not seem to be the only particle in the nucleus. As they studied atomic disintegration, they kept seeing that the atomic number (number of protons in the nucleus, equivalent to the positive charge of the atom) was less than the atomic mass (average mass of the atom). For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass. One leading explanation was that there were electrons and additional protons in the nucleus as well -- the protons still contributed their mass but their positive charge was canceled out by the negatively charged electrons. So in the helium example, there would be four protons and two electrons in the nucleus to yield a mass of 4 but a charge of only 2. Rutherford also put out the idea that there could be a particle with mass but no charge. He called it a neutron, and imagined it as a paired proton and electron. There was no evidence for any of these ideas. Chadwick kept the problem in the back of his mind while working on other things. Experiments in Europe caught his eye, especially those of Frederic and Irene Joliot-Curie. They used a different method for tracking particle radiation. Chadwick repeated their experiments but with the goal of looking for a neutral particle -- one with the same mass as a proton, but with zero charge. His experiments were successful. He was able to determine that the neutron did exist and that its mass was about 0.1 percent more than the proton's. He published his findings with characteristic modesty in a first paper entitled "Possible Existence of Neutron." In 1935 he received the Nobel Prize for his discovery.

Na 11 22.99 Atomic Number Na 11 22.99 Atomic number will be the smallest number shown! Atomic # = number of protons in an atom All atoms of given element have the same atomic number Atoms are neutral therefore…. Positive charge = negative charge OR Number of protons = number of electrons

Mass Number Mass number = number of protons & neutrons Electron
Nucleus Mass number = Atomic number = Element = 12 6 Carbon (C)

Isotopes SAME: DIFFERENT:
Atoms of the same element having different number of neutrons SAME: DIFFERENT: Element # P # e # Neutrons Masses # Neutrons = mass number – atomic number

C C C-12 C-14 Isotopes of Carbon or or 6 P 6 P 12 14 6 e 6 6 6 e 6 N
Note: Use the mass number on the periodic table, unless I tell you otherwise. Isotopes of Carbon C-12 C-14 or or 6 P 6 P 12 14 C C 6 e 6 6 6 e 6 N 8 N Nucleus Nucleus

Isotopes of Hydrogen Hydrogen – 1 (protium) Hydrogen – 2 (deuterium)
(tritium) 1 P 1 P 1 P 1 2 3 H 1 e H 1 e H 1 e 1 1 1 0 N 1N 2 N Radioactive

“Heavy Water”

Atomic Mass Mass of atom relative to Carbon-12 (standard)
Unit = atomic mass unit or amu 1 amu = 1/12 mass of a C-12 atom Amu is roughly equal to the mass of one proton or neutron (there are 12 in C so 1 amu is 1 of those 12). With exception of C-12 (the random standard) an atom’s mass in amu is never precisely the same as its mass number. Mass of Cl-35 is equal to amu (not 35). Amu refers to the sum of the protons and neutrons (they are roughly the same mass whereas electrons are so small they don’t “weigh” in) BUT scientists are precise and it is not precise to define an atomic mass unit as the mass of a proton or neutron because protonos and neutrons do not have the exact same mass. So scientists choose to define amu in terms of arbitrary standardC-12 meaning C-12 is exactly 12 amu so 1 amu is 1/12th of this.

Let’s try it. Atomic mass on the Periodic Table is the average atomic mass, based on abundances of each isotope in nature. What is the atomic mass of Li? What is the atomic mass of Cl? What is the atomic mass of As 6.94 amu 35.45 amu 74.92 amu

Why are they fractional?
Why is B amu and not just 11? There are two isotopes of B Scientists take an average of the isotopes to calculate the atomic mass Which one is more abundant in nature? B 10 5 B 11 5

*NOTE Atomic masses are generally fractional
Mass numbers are rounded to the nearest whole number. For example: Carbon’s atomic mass is 12.01 Carbon’s mass number is 12 What about Be, Na, B?

Calculating the average atomic mass
Cl: 75.5% is Cl-35 (atomic mass = amu) 24.5% is Cl-37 (atomic mass = amu) What is the atomic mass on the Periodic Table? .755(34.97) (36.97) = = 35.5 amu

Put it all together F 19 Model of the atom 9 9 P 10 N Electron Cloud
Nucleus # Neutrons = atomic mass – atomic number

I need some volunteers! Li K O Na Draw the model on the board. 7 3 39
19 O 16 8 Na 23 11

Nuclear Reactions The composition of the nucleus is changed.
As of July 2008, there were more than 430 operating nuclear power plants and, together, they provided about 15 percent of the world's electricity in Of these 31 countries, some depend more on nuclear power than others. For instance, in France about 77 percent of the country's electricity comes from nuclear power [source: NEI]. Lithuania comes in second, with an impressive 65 percent. In the United States, 104 nuclear power plants supply 20 percent of the electricity overall, with some states benefiting more than others. Despite all the cosmic energy that the word "nuclear" invokes, power plants that depend on atomic energy don't operate that differently from a typical coal-burning power plant. Both heat water into pressurized steam, which drives a turbine generator. The key difference between the two plants is the method of heating the water. While older plants burn fossil fuels, nuclear plants depend on the heat that occurs during nuclear fission, when one atom splits into two. Uranium, for example, constantly undergoes spontaneous fission very slowly. This is why the element emits radiation, and why it's a natural choice for the induced fission that nuclear power plants require. Uranium is a common element on Earth. It's been around since the planet formed. Uranium-238 (U-238) has an extremely long half-life (the time it takes for half its atoms to decay) of 4.5 billion years. Therefore, it's still present in fairly large quantities. U-238 makes up 99 percent of the uranium on Earth, while uranium-235 (U-235) makes up about 0.7 percent of the remaining uranium found naturally. Uranium-234 is even rarer, formed by the decay of U-238. U-238 goes through many stages of decay in its life span, eventually forming a stable isotope of lead, so U-234 is just one link in that chain. Uranium-235 has an interesting property that makes it handy for the production of both nuclear power and nuclear bombs. U-235 decays naturally, just as U-238 does, by alpha radiation: It throws off an alpha particle, or two neutrons and two protons bound together. U-235 also undergoes spontaneous fission a small percentage of the time. However, U-235 is one of the few materials that can undergo induced fission. If a free neutron runs into a U-235 nucleus, the nucleus will absorb the neutron, become unstable and split immediately. In fact, under reactor conditions, one neutron ejected from each fission causes another fission to occur. As soon as the nucleus captures the neutron, it splits into two lighter atoms and throws off two or three new neutrons (the number of ejected neutrons depends on how the U-235 atom splits). The process of capturing the neutron and splitting happens very quickly, on the order of picoseconds (1x10-12 seconds). The splitting of an atom releases an incredible amount of heat and gamma radiation, or radiation made of high-energy photons. The two atoms that result from the fission later release beta radiation (super fast electrons) and gamma radiation of their own as well. The energy released by a single fission comes from the fact that the fission products and the neutrons, together, weigh less than the original U-235 atom. The difference in weight is converted directly to energy at a rate governed by the equation E = mc2. The decay of a single U-235 atom releases approximately 200 MeV (million electron volts). That may not seem like much, but there are a lot of uranium atoms in a pound (0.45 kg) of uranium. So many, in fact, that a pound of highly enriched uranium as used to power a nuclear submarine is equal to about a million gallons of gasoline. However, for all of this to work, a sample of uranium must be enriched so that it contains 2 to 3 percent more U-235. Three-percent enrichment is sufficient for nuclear power plants, but weapons-grade uranium is composed of at least 90 percent U-235. Chernobyl– US is much safer; that is worse case scenario. We have domes covering our plants in effort to contain a possible spill. The biggest problem is what to do with the waste.

Stable Nuclei P Stable nuclei are NOT radioactive
Stable nuclei are elements #1-83 (#84are radioactive) Strong nuclear forces = attraction between particles in nucleus that hold it together VERY STRONG! P Beyond 83 all forms are radioactive but before there are some versions of those elements that are radioactive We believe that there are four fundamental forces in the universe; gravity, and the electromagnetic, weak (The weak force is responsible for radioactive decay. It actually makes neutrons turn into protons, amongst other things, and every type of matter particle experiences it.) and strong forces. Quarks, we believe, are among the few fundamental particles in the universe. There are six types of quarks (up, down, charm, strange, top, and bottom). The lightest quarks — called up and down — are the most common. Quarks are bound to each other by the strongest force in the universe. Called simply the strong force, this enormous force binds them so tightly that one quark cannot exist by itself. Strong force overrides the electromagnetic force (which would cause the protons to repel each other). Glued by the strong force, quarks are the building blocks of matter as we know it. Understanding quarks and the strong force is fundamental to the universe, our world, and ourselves.

#1-20 equal number of protons & neutrons for stable nuclei
#21-83 nuclei need more & more neutrons to be stable #84 radioactive (all isotopes Belt of Stability A region on a neutron to proton graph that represents stable nuclides Notes to Consider: All nuclides with Z>83 are unstable Z values lower than 20 have neutron/proton = 1 As Z increases above 20, the neutron/proton ratio increases. ex. 90Zr = 1.25, 120Sn = 1.4, 200Hg = 1.54. 4. Region above the belt represents excess neutrons 5. Region below the belt represents excess protons

Types of Radioactive Decay
1. Alpha particles 2. Beta particles 3. Gamma particles Radiation is dangerous because it strips away the electrons from atoms in cells, causing them to malfunction.

= He Ra  α + Rn Alpha Particles 4 4 2 2
Consists of 2 protons & 2 neutrons Has a +2 charge Identical to a He-4 nucleus Stopped by paper Move two to the left when decay Examples of some alpha emitters: radium, radon, uranium, thorium Rutherford found helium for the first time on earth by sealing radioactive material in a tube for months. He got the Nobel prize for this work. The helium nucleus formed by alpha radiation is very energetic due to conversion of mass to energy and it travels at a very fast speed. This speed is converted to heat and is the source of half of the earths heat. Eg. Uranium-238 goes to thorium-234, a completely different element. One of the reasons that it is difficult to contain radioactive waste is that the decay process creates these tiny alpha particle-bullets that rip holes through the container. Ra  α + Rn 222 88 226 86 4 2

 α  α Pa + Ac + U Pu Alpha decay problems Pa Pu
Write the nuclear equation for the alpha decay of Pa 91 231 Pa 231 91  α 4 2 + Ac 89 227 Write the nuclear equation for the alpha decay of Pu 94 244 + U 92 240 Pu 244 94  α 2 4

β = e I  e + Xe Beta particles -1 -1
-1 -1 = e High speed electron is emitted out from atom -1 charge Stopped by heavy clothing Neutron changes into a proton & an electron Move one to the right when decay Beta decay: a neutron in a nucleus spontaneously decays into a proton, an electron, and a neutrino, thus creating a different element. Carbon-14 > nitrogen-14. Due to a weak force. Stream of high speed electrons- not electrons in motion around nucleus Beta radiation comes from changes in nucleus: nuetrons changes into a proton and a electron, proton remains in nucleus, electron ( particle) propelled out of nucleus at high speeds. Mass # is zero 100x more penetrating that alpha radiation Able to pass through clothing and damage skin The first recognizable particle after the big bang event was the neutron, which then underwent beta decay to form the protons and electrons that now make up the universe. Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35 I  e + Xe 131 53 54 -1

 e + Ra  e + V Fr Ti Beta Decay problems Fr Ti
Write a nuclear equation for the beta decay of Fr 223 87 Fr 223 87  e -1 + Ra 88 223 Write a nuclear equation for the beta decay of Ti 50 22 Ti 50 22  e -1 + V 23 50

Gamma Radiation High energy Radiant energy 0 charge, 0 mass
High energy Radiant energy 0 charge, 0 mass Most penetrating Stopped by lead or concrete Gamma radiation: nuclear particles shift energy levels, like electrons undergoing a quantum leap, and X-rays or gamma rays are emitted. Very dangerous does not consist of particles Penetrates solid material including body tissues Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and technetium-99m. Gamma rays or gamma-ray (denoted as γ) are forms of electromagnetic radiation (EMR) or light emissions of a specific frequency produced from sub-atomic particle interaction, such as electron-positron annihilation and radioactive decay; most are generated from nuclear reactions occurring within the interstellar medium of space. Gamma rays are generally characterized as electromagnetic radiation, having the highest frequency and energy, and also the shortest wavelength, within the electromagnetic spectrum, i.e. high energy photons. Due to their high energy content, they are able to cause serious damage when absorbed by living cells.

Recap Half-life: the amount of time it takes half of a batch of radioactive material to decay. Ranges from less than a second to billions of years, depending upon the isotope Pierre Curie ( ) Marie Curie ( ) By the time he met Marie Sklodowska, Pierre Curie had already established an impressive reputation. In 1880, he and his brother Jacques had discovered piezoelectricity whereby physical pressure applied to a crystal resulted in the creation of an electric potential. He also had made important investigations into the phenomenon of magnetism including the identification of a temperature, the curie point, above which a material's magnetic properties disappear. However, shortly after his marriage to Marie in 1895, Pierre subjugated his research to her interests. Together, they began investigating the phenomenon of radioactivity recently discovered in uranium ore. Although the phenomenon was discovered by Henri Becquerel, the term radioactivity was coined by Marie. After chemical extraction of uranium from the ore, Marie noted the residual material to be more "active" than the pure uranium. She concluded that the ore contained, in addition to uranium, new elements that were also radioactive. This led to their discoveries of the elements of polonium and radium, but it took four more years of processing tons of ore under oppressive conditions to isolate enough of each element to determine its chemical properties. For their work on radioactivity, the Curies were awarded the 1903 Nobel Prize in physics. Tragically, Pierre was killed three years later in an accident while crossing a street in a rainstorm. Pierre's teaching position at the Sorbonne was given to Marie. Never before had a woman taught there in its 650 year history! Her first lecture began with the very sentence her husband had used to finish his last. In his honor, the 1910 Radiology Congress chose the curie as the basic unit of radioactivity: the quantity of radon in equilibrium with one gram of radium (current definition: 1 Ci = 3.7x1010 dps). A year later, Marie was awarded the Nobel Prize in chemistry for her discoveries of radium and polonium, thus becoming the first person to receive two Nobel Prizes. For the remainder of her life she tirelessly investigated and promoted the use if radium as a treatment for cancer. Marie Curie died July 4, 1934, overtaken by pernicious anemia no doubt caused by years of overwork and radiation exposure.

Other Nuclear Reactions
Fission is splitting of the nucleus Fusion is joining of nuclei hydrogen bomb or H-bomb,weapon deriving a large portion of its energy from the nuclear fusion of hydrogen isotopes. In an atomic bomb, uranium or plutonium is split into lighter elements that together weigh less than the original atoms, the remainder of the mass appearing as energy. Unlike this fission bomb, the hydrogen bomb functions by the fusion, or joining together, of lighter elements into heavier elements. The end product again weighs less than its components, the difference once more appearing as energy. Because extremely high temperatures are required in order to initiate fusion reactions, the hydrogen bomb is also known as a thermonuclear bomb.Read more: hydrogen bomb — Infoplease.com The presumable structure of a thermonuclear bomb is as follows: at its center is an atomic bomb; surrounding it is a layer of lithium deuteride (a compound of lithium and deuterium, the isotope of hydrogen with mass number 2); around it is a tamper, a thick outer layer, frequently of fissionable material, that holds the contents together in order to obtain a larger explosion. Neutrons from the atomic explosion cause the lithium to fission into helium, tritium (the isotope of hydrogen with mass number 3), and energy. The atomic explosion also supplies the temperatures needed for the subsequent fusion of deuterium with tritium, and of tritium with tritium (50,000,000°C and 400,000,000°C, respectively). Enough neutrons are produced in the fusion reactions to produce further fission in the core and to initiate fission in the tamper.Since the fusion reaction produces mostly neutrons and very little that is radioactive, the concept of a “clean” bomb has resulted: one having a small atomic trigger, a less fissionable tamper, and therefore less radioactive fallout. Carrying this progression further would result in the suggested neutron bomb,. which would have a minimum trigger and a nonfissionable tamper; there would be blast effects and a hail of lethal neutrons but almost no radioactive fallout; this theoretically would cause minimal physical damage to buildings and equipment but kill most living things. The theorized cobalt bomb. is, on the contrary, a radioactively “dirty” bomb having a cobalt tamper. Instead of generating additional explosive force from fission of the uranium, the cobalt is transmuted into cobalt-60, which has a half-life of 5.26 years and produces energetic (and thus penetrating) gamma rays. The half-life of Co-60 is just long enough so that airborne particles will settle and coat the earth's surface before significant decay has occurred, thus making it impractical to hide in shelters.Read more: hydrogen bomb — Infoplease.com

Fission Chain Reaction
If these neutrons hit other nuclei, they will split also and a chain reaction will begin. In a reactor, a controlled chain reaction is created in rods of uranium enriched in U-235. These rods are the thickness of a pencil. This reaction heats water which causes other water to boil, driving turbines which create electricity. Waste. Meltdown.

Fusion Weapons: fission or fusion? Fission bombs have a U-235 core, about the size of a grapefruit. Since we need a critical amount of U-235 in a given volume, we store it just short of the required density. Then when the bomb is to go off, we compress it with a chemical explosion, thereby setting off the fission event. Fusion bombs are made by surrounding a core of H with fission bombs. They go off and increase the pressure around the H so it then fuses to form He, giving off tremendous amounts of energy.

The Mole

The Mole 1 mole contains 6.02 x 1023 atoms
The atomic mass of an element expressed in grams is: 1 mole of that substance OR its gram-atomic mass (GAM)

What is a mole really?

Lets try it. 16.00 g of O = 1 mol of O atoms and contains
6.02 x 1023 atoms _____ g of S = 1 mol of S atoms and contains _________ atoms. 32.06 6.02 x 1023 _____ g of Mg = 1mol of Mg atoms and contains _________ atoms. 24.31 6.02 x 1023

Put it together 1 mole = GAM (from P.T.) and
1 mole = 6.02 x 1023 particles Avogadro’s Number

Mole conversions What is the mass in grams of 4.00 moles of krypton (Kr) atoms? x = 4.00 moles Kr 83.80 g Kr = 335.2 335 g Kr 1 mole Kr 83.80 g Kr = 1 mole Kr From Periodic Table

Practice What is the mass of 0.30 moles of sulfur (S)? x = 0.30 mol S
32.06 g S = 9.618 9.6 g of S 1 mol S 32.06 g S = 1 mole S

More practice How many moles of boron (B) are present in 22 grams? x =
1 mol B 22 g B = 2.035 2.0 mol of B 10.81 g B 10.81 g B = 1 mole B

Again P How many moles are there in 9.3 g of phosphorous (P)? 9.3 g
x = 1 mole P .30 mol of P = 30.97 g P 1 mole P = g P

Last time Find the number of moles in 22.5 g of beryllium (Be). = x
1 mol Be 22.5 g Be = 2.50 mol of Be 9.01 g Be 1 mole Be = 9.01 g Be

g The mole map # particles (atoms) 6.02 x 1023 atoms 1 mol MOLE 1 mol
GAM GAM 1 mol g

MOLE A mole (mol) is defined as the number of atoms in exactly 12 grams of Carbon-12. The mole is the SI unit for the amount of a substance.

The Mole Start of Chem Calculations:
The Carbon-12 based Atomic Mass Scale- By definition, an atom of this isotope is defined as having the mass of exactly amu (atomic mass units) . In other words, an amu is defined as 1/12th of the mass of one atom of Carbon-12. Why Carbon-12? Carbon is a very common element, available to any scientist and by choosing the amu to be this size, the atomic masses of nearly all the other elements are almost whole numbers, with the lightest atom having a mass of ~1. Hydrogen-1= amu when Carbon is assigned a mass of exactly 12. C-12 most abundant isotope of C When we mass out a sample of an element such that its mass in grams is numerically equal to the elements atomic weight we always obtain the same number of atoms no matter what element we choose. 12.0 g C = same # as 16g of O or 32.1 g S or 55.8gFe This relationship also extends to ompounds Formula mass of H2O= 18.0 amu NaCl

Mol Molar Mass [g/mol]= mass of one mole in grams to two decimal places off the periodic table. Grams MOL Molecules 1 mol=1GAM=6.02 x1023molecules 6.02 x 1023molecules - Avogadro’s # Avogadro’s number: is a defined mass of an element (it’s atomic weight) there is a precise number of atoms. A mole of eggs would fill all of the oceans on earth more than 30 million times over. It would take 10 billion chickens laying 10 eggs per day for more than 10 billion years to lay a mole of eggs. Mole is used when talking about atoms and molecules. Very small things. A drop of water the size of the period at the end of a sentence on your paper would contain 10 trillion water molecules rather than talk about trillions and quadrillions we use the mole. Amadeo Avogadro no lenses with resolving power or balances fine enough to measure an individual atom.

CONVERSIONS-dimensional Analysis (again!)
Mole: amount of substance in grams A sample of any element with a mass equal to that elements atomic mass in grams will contain precisely one mole of atoms (6.02 x 1023)

PRACTICE: COMPLETE FORMULA WS COMPLETE PROBLEM WS

Determine which of Dalton’s postulates explains each observation?
Matter can never really be thrown away. That is one reason that recycling is important The formula for ethanol is C2H6O, and the formula for acetic acid in vinegar is C2H4O2 There is no difference between Cu found in an ancient Mayan necklace and Cu wire freshly made from Cu ore. Zn is a metal that is softer that Fe and it reacts more readily with acid than Fe does. When Methane, CH4, Burns, it combines with O2, in the air to form molecules of H2O and CO2.

I. Law of Conservation of Matter: Discovered by:?
II. Law of Constant Composition: Joseph Proust A given compound always contains the same elements in the same proportions by mass Water= 11% H2 , 89%O2 French Chemist 100% natural vs synthetic compound properties come from the identity and arrangement of atoms not the place where the Atoms were assembled. Mixture Brass is an alloy- Cu and Zn varying proportions Can be 10% -45% and still considered an alloy Ethlyene glycol- c2h6o2– 51.56%o2,38.70%c,9.74%h Iron Oxide= FeO= 25% O2, 75%Fe

JJ Thompson (1897) J.J. Thompson is the person who is credited for discovering the electron. Thompson created a tube that had a positively charged anode on one side and a negatively charged cathode on the other side. Thompson then applied a magnet to the middle of the tube and discovered that negatively charged particles were emanating towards the positive magnetic field. From this, Thompson concluded that negatively charged particles, called electrons, were present in atoms. Couldn’t find positive charge but knew atoms were netural. Lates 1800’s Watched the deflection of charges in a cathode ray tube and put forth the idea that atoms were composed of + and – charges. The negative charges were called electrons, and thomson guessed that they were sprinkled throughout the positively charged atom like choc chips sprinkled throughout a blob of cookie dough. Thomson knew the rays must have come from the atoms of the cathode because most of the atoms in the air had been pumped out of the tube. Because the cathode ray came from negatively charged cathode , thomson reasoned that the ray was negatively charged. DEMO- TV- MAGNETS

CATHODE RAY TUBE JJ Thompson conducted a series of systemic studies on cathode rays Watched the deflection of charges in a CRT and put forth the idea that Atoms were composed of (+) and (-) charges. Negative charges = electrons Electron mass ratio= 1.76 x 108 C/g COULD NOT DETERMINE MASS! Thomson thought of a new approach. A charged particle will normally curve as it moves through an electric field, but not if it is surrounded by a conductor. Thomson suspected that the traces of gas remaining in the tube were being turned into an electrical conductor by the cathode rays themselves. To test this idea, he took great pains to extract nearly all of the gas from a tube, and found that now the cathode rays did bend in an electric field after all. Thompson preformed experiments that involved passing electric current through gases at low pressure. Seal gases in glass tubes – fitted at both ends with metal disks called electrodes. Electrodes connected to a source of electricity- (battery) Electrons travel as a ray- vacumn out tube- line tube with fluorescent material that glows in presence of electricity. Expt. Used to prove negative charge is made up of particles. Anode has a hole in it to allow a fraction of the cathode ray to pass through. + plate on top- magnetic field on – field goes up so particles carry charge in the middle both forces cancel each other out. BOTH magnetic plates can deflect the rays path. The ray will eventually hit the other end of the tube which is coated with fluorescent material. Changing gases or electrodes does not change effect. Magnetic and electric fields deflect the rays path in a mathematically predictable way. Atoms have substructure. Thompson could not determine mass of Electron but did determine the ratio of electrons electrical charge to it’s mass 1.76 x 10^8 coulombs/gram C= SI unit of electrical charge Electrical current: moving stream of electrical charge Cathode: negative electrode Anode: positive electrode

“Could anything at first sight seem more impractical than a body which is so small that its mass is an insignificant fraction of the mass of an atom of hydrogen?" -- J.J. Thomson.

JJ Thompson Cathode Ray Tube (CRT) Discovered the electron
J. J. Thompson- studied electrical current and discovered atomic structure. When: 1897 Where: England What: Thompson discovered that electrons were smaller particles of an atom and were negatively charged. Why: Thompson knew atoms were neutrally charged, but couldn’t find the positive particle. Born Joseph John Thomson December 18th August 30th, 1940 Attended University of Manchester where he studied engineering, mathematics, physics and chemistry Planned to be an engineer, but his dream was to carry out his own research Married Rose Paget, daughter of a physics professor at Cambridge Awarded the Nobel Prize for Physics because of his investigations of the passage of electricity through gases Taught Ernest Rutherford Had 2 kids, George and Joan His son, George, was awarded the Nobel Prize for Physics

Michael Faraday Suggested that the structure of atom
was somewhat related to electricity. Atoms contain particles that have electrical charge. Story of electricity and the atom includes a certain American whose name you should find very familiar? The English chemist and physicist Michael Faraday, b. Sept. 22, 1791, d. Aug. 25, 1867, is known for his pioneering experiments in electricity and magnetism. Many consider him the greatest experimentalist who ever lived. Several concepts that he derived directly from experiments, such as lines of magnetic force, have become common ideas in modern physics. During the initial years of his scientific work, Faraday occupied himself mainly with chemical problems. He discovered two new chlorides of carbon and succeeded in liquefying chlorine and other gases. He isolated benzene in 1825, the year in which he was appointed director of the laboratory. Faraday's research into electricity and electrolysis was guided by the belief that electricity is only one of the many manifestations of the unified forces of nature, which included heat, light, magnetism, and chemical affinity. Although this idea was erroneous, it led him into the field of electromagnetism, which was still in its infancy.

Benjamin Franklin Made distinction between
2 kinds of electrical charge, Positive (+) and negative (-) Opposite charges: attract. Like Charges: repel Where do + and – charges come from? What are their physical properties? Led to his discovery of another Electrical device called a battery. While experimenting w/ electricity B. Franklin noticed the resemblance of an electrical spark to lightening. To prove his point = metal key attract electrical charges. If he had been able to measure some of the properties of the lightening that struck his kite, he would have found that the electrical current of the lightening bolt would have been about 20,000 amps. Temp of the plasma in the bolt would have been 30,000K. Mid-1800-s Scientists began to investigate the way electric currents travelled thru partially evacuated glass tubes, or tubes with very thin air in them. A century after Franklin’s expts scientists studying the Cathode ray tube could answer these questions.

Question: How did Rutherford use the results of his alpha scattering experiment experiment to challenge the plum pudding model of the atom? How does Rutherford’s model of the atom differ from the plum pudding model? The plum puddig model of the atom suggested that positive and negative charges were evenly distributed throughout an atoms interior. In Rutherfords alpha scattering expt. Only a few particles were deflected by the gold foil. This led Rutherford to believe that most of the atom’s mass was concentrated near the center of the atom rather than distributed throughout. New Modelthe electrons orbited a positively charged nucleus.

Radioactivity Henri Becquerel (1896)
Discovered that U exhibits radioactivity (spontaneous emission of radiation from an element) Uranium one of many naturally radioactive elements The material Becquerel chose to work with was potassium uranyl sulfate, K2UO2(SO4)2, which he exposed to sunlight and placed on photographic plates wrapped in black paper. When developed, the plates revealed an image of the uranium crystals. Becquerel concluded "that the phosphorescent substance in question emits radiation which penetrates paper opaque to light." Initially he believed that the sun's energy was being absorbed by the uranium which then emitted X rays. Further investigation, on the 26th and 27th of February, was delayed because the skies over Paris were overcast and the uranium-covered plates Becquerel intended to expose to the sun were returned to a drawer. On the first of March, he developed the photographic plates expecting only faint images to appear. To his surprise, the images were clear and strong. This meant that the uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material. Later, Becquerel demonstrated that the radiation emitted by uranium shared certain characteristics with X rays but, unlike X rays, could be deflected by a magnetic field and therefore must consist of charged particles. For his discovery of radioactivity, Becquerel was awarded the 1903 Nobel Prize for physics.

Radioactivity Radioactivity: spontaneous release of energetic particles or photons from the nuclei. Original nucleus decomposes, decays to form a new nucleus, releasing radiation in the process. There are 3 types of radioactive decay. 1.Alpha 2.Beta 3.Gamma Radioactive decay- when an atom emits ,, radiation. Discovered by Antoine Becquerel in 1896 with a photographic plate exposed by radiation from minerals in a drawer. Much of the early research was conducted by Marie Curie, the first 2 time Nobel prize winner. She died from radiation exposure.

Radioactivity Marie and Pierre Curie
- Isolated 2 other radioactive elements: Polonium and Radium Marie Curie ca Inset: Pierre Curie (Marie's favorite picture of her husband). Pierre Curie ( ) Marie Curie ( ) By the time he met Marie Sklodowska, Pierre Curie had already established an impressive reputation. In 1880, he and his brother Jacques had discovered piezoelectricity whereby physical pressure applied to a crystal resulted in the creation of an electric potential. He also had made important investigations into the phenomenon of magnetism including the identification of a temperature, the curie point, above which a material's magnetic properties disappear. However, shortly after his marriage to Marie in 1895, Pierre subjugated his research to her interests. Together, they began investigating the phenomenon of radioactivity recently discovered in uranium ore. Although the phenomenon was discovered by Henri Becquerel, the term radioactivity was coined by Marie. After chemical extraction of uranium from the ore, Marie noted the residual material to be more "active" than the pure uranium. She concluded that the ore contained, in addition to uranium, new elements that were also radioactive. This led to their discoveries of the elements of polonium and radium, but it took four more years of processing tons of ore under oppressive conditions to isolate enough of each element to determine its chemical properties. For their work on radioactivity, the Curies were awarded the 1903 Nobel Prize in physics. Tragically, Pierre was killed three years later in an accident while crossing a street in a rainstorm. Pierre's teaching position at the Sorbonne was given to Marie. Never before had a woman taught there in its 650 year history! Her first lecture began with the very sentence her husband had used to finish his last. In his honor, the 1910 Radiology Congress chose the curie as the basic unit of radioactivity: the quantity of radon in equilibrium with one gram of radium (current definition: 1 Ci = 3.7x1010 dps). A year later, Marie was awarded the Nobel Prize in chemistry for her discoveries of radium and polonium, thus becoming the first person to receive two Nobel Prizes. For the remainder of her life she tirelessly investigated and promoted the use if radium as a treatment for cancer. Marie Curie died July 4, 1934, overtaken by pernicious anemia no doubt caused by years of overwork and radiation exposure. Multiple laureates Since the establishment of the Nobel Prize, four people have received two Nobel Prizes:[20] Maria Skłodowska-Curie: in Physics 1903, for the discovery of radioactivity; and in Chemistry 1911, for the isolation of pure radium Linus Pauling: in Chemistry 1954, for the hybridized orbital theory; and Peace 1962, for nuclear test-ban treaty activism; John Bardeen: in Physics 1956, for the invention of the transistor; and Physics 1972, for the theory of superconductivity; and Frederick Sanger: in Chemistry 1958, for structure of the insulin molecule; and in Chemistry 1980, for virus nucleotide sequencing. Otto Heinrich Warburg could have been among them, but he was prevented by the Nazi government from accepting his second Nobel Prize for Medicine in 1944.[21] As a group, the International Committee of the Red Cross (ICRC) has received the Nobel Peace Prize three times: in 1917, 1944, and The first two prizes were specifically in recognition of the group's work during the world wars. The United Nations High Commissioner for Refugees (UNHCR) has won the Peace Prize twice: in 1954 and 1981. Family laureates A number of families have included multiple laureates.[20] The Curie family claim the most Nobel Prizes, with five: Maria Skłodowska-Curie, Physics 1903 and Chemistry 1911 Her husband Pierre Curie, Physics 1903 Their daughter Irène Joliot-Curie, Chemistry 1935 – artificial radioactivity- decay Their son in law Frederic Joliot-Curie, Chemistry 1935 Furthermore, Henry Labouisse, the husband of the Curies' second daughter Ève, was the director of UNICEF when it won the Nobel Peace Prize in 1965. Age extremes William Lawrence Bragg, who was only 25 when he shared the 1915 Nobel Prize in Physics with his father William Henry Bragg, is the youngest person ever to win a Nobel Prize.[22] Doris Lessing, 87, is the oldest woman ever to win a Nobel Prize when she was awarded the 2007 Nobel Prize in Literature. [23] ****From 1928 Irène and Frédéric combined their research interests on the study of atomic nuclei. Though their experiments identified both the positron and the neutron they failed to interpret the significance of the results and the discoveries were later claimed by C.D. Anderson and James Chadwick respectively.

Ernest Rutherford Student of JJ Thompson
Gold Foil Experiment (α scattering expt) Began in depth study of radioactivity- Found that U emits two forms of radiation and developed his nuclear model of atom. Who: Ernest Rutherford When: 1911 Where: England What: Conducted an experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core. Why: He knew that atoms had positive and negative particles, but could not decide how they were arranged. Who was Ernest Rutherford? Rutherford, Ernest ( ): Born in New Zealand, Rutherford studied under J. J. Thomson at the Cavendish Laboratory in England. His work constituted a notable landmark in the history of atomic research as he developed Bacquerel's discovery of Radioactivity into an exact and documented proof that the atoms of the heavier elements, which had been thought to be immutable, actually disintegrate (decay) into various forms of radiation. Rutherford was the first to establish the theory of the nuclear atom and to carry out a transmutation reaction (1919) (formation of hydrogen and and oxygen isotope by bombardment of nitrogen with alpha particles). Uranium emanations were shown to consist of three types of rays, alpha (helium nuclei) of low penetrating power, beta (electrons), and gamma, of exceedingly short wavelength and great energy. Ernest Rutherford also discovered the half-life of radioactive elements and applied this to studies of age determination of rocks by measuring the decay period of radium to lead-206.

Alpha decay Alpha decay: a nucleus emits an alpha particle consisting of 2 neutrons and 2 protons, which is a helium nucleus. Rutherford found helium for the first time on earth by sealing radioactive material in a tube for months. He got the Nobel prize for this work. The helium nucleus formed by alpha radiation is very energetic due to conversion of mass to energy and it travels at a very fast speed. This speed is converted to heat and is the source of half of the earths heat. Eg. Uranium-238 goes to thorium-234, a completely different element. One of the reasons that it is difficult to contain radioactive waste is that the decay process creates these tiny alpha particle-bullets that rip holes through the container.

Alpha and beta decay practice problems:
NUCLEAR EQUATION- to keep track of the reaction components Alpha decay Example: Ra Rn He U 1/2 life 4.5 billion years --- in 4.5 billion years 1/2 as much U on Earth as there is today. U would have changed into other elements. Nucleus rejects a helium nucleus or alpha particle and becomes A smaller nucleus with less positive charge

Beta decay Beta decay: a neutron in a nucleus spontaneously decays into a proton, an electron, and a neutrino, thus creating a different element. Carbon-14 > nitrogen-14. Due to a weak force. Stream of high speed electrons- not electrons in motion around nucleus Beta radiation comes from changes in nucleus: nuetrons changes into a proton and a electron, proton remains in nucleus, electron ( particle) propelled out of nucleus at high speeds. Mass # is zero 100x more penetrating that alpha radiation Able to pass through clothing and damage skin The first recognizable particle after the big bang event was the neutron, which then underwent beta decay to form the protons and electrons that now make up the universe. Move one to the right when decay Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35

Beta Decay Problems I Xe +  Beta Decay Example: 131 131 0 53 54 -1
I Xe  Turns a neutron in the nucleus into a proton, ejecting a beta Particle (-) or electron in the process. In Radioactive Decay- sums of mass # and Atomic # are the same before and after the rxn.

Gamma decay Gamma radiation: nuclear particles shift energy levels, like electrons undergoing a quantum leap, and X-rays or gamma rays are emitted. Very dangerous does not consist of particles Penetrates solid material including body tissues Stopped by lead or concrete Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and technetium-99m. Gamma rays or gamma-ray (denoted as γ) are forms of electromagnetic radiation (EMR) or light emissions of a specific frequency produced from sub-atomic particle interaction, such as electron-positron annihilation and radioactive decay; most are generated from nuclear reactions occurring within the interstellar medium of space. Gamma rays are generally characterized as electromagnetic radiation, having the highest frequency and energy, and also the shortest wavelength, within the electromagnetic spectrum, i.e. high energy photons. Due to their high energy content, they are able to cause serious damage when absorbed by living cells.

Radiation is dangerous because it strips away the electrons from atoms in cells, causing them to malfunction.

Radiation Experiment (+) (-)
Alpha and beta radiation made up of particles Alpha = 2+ charge 4/2 alpha or HE Beta = high speed electrons 0/-1 beta or e Gamma not composed of particles Chart Alpha 2+ charge He nucleus low penetrating ability stopped by paper Beta charge electron med stopped by heavy clothing Gamma no charge high energy non high, stopped by lead (similar to xrays) particle radiation Proves atom more complex than dalton thought. Alpha particles way of probing the atoms structure.

Half Life Contents [hide]
Half-life: the amount of time it takes half of a batch of radioactive material to decay. Ranges from less than a second to billions of years, depending upon the isotope. Radiometric dating: The technique of measuring quantities of isotopes in order to determine time scales. e.g.: the ratio of radioactive carbon-14 to carbon-13 in an organism at the time of its death is the same as the general environment. After death, no more carbon is taken in, so the % of C-14 goes down as it decays into N-14. Half decays every 5700 years, so time of death can be calculated. Eg the Shroud of Turin and the Dead Sea Scrolls were dated at the University of Arizona with this technique. EXTRA CREDIT ON THE TEST: LOOK UP HOW RADIOACTIVE DATING WAS USED FOR THE KENNEWICK MAN AND THE Haraldskｾr Woman We measure the stability of a radioactive compound in terms of a quantity that is called "half-life". Decay chains: isotopes can decay into other unstable isotopes and these new isotopes can also decay. Radon forms this way from the decay of U238. It is a gas that can concentrate in basements with a short half life and with daughters that have short half-lives. The ensuing radiation is dangerous. The Haraldskｾr Woman is an Iron Age bog body naturally preserved in a bog in Jutland, Denmark. Labourers discovered the body in 1835 while excavating peat on the Haraldskｾr Estate. Disputes regarding the age and identity of this well preserved body were settled in 1977, when radiocarbon dating determined conclusively that her death occurred around 500 BC.[1] This archaeological find was one of the earliest bog bodies discovered, the other two known being Tollund Man (Denmark) and Lindow Man (England).The body of the Haraldskｾr Woman is remarkably preserved due to the anaerobic conditions and tannins of the peat bog in which she was found. Not only was the intact skeleton found, but also the skin and internal organs. Her body lies in state in an ornate glass-covered coffin, allowing viewing[2] of the full frontal body, inside the Church of Saint Nicolai in central Vejle, Denmark. KENNEWICK MAN:The remains were first examined by anthropologist James Chatters. After ten separate visits, Chatters was able to collect three hundred and fifty pieces of bone as well as the skull, which completed almost a full skeleton.[2] The cranium was fully intact except for two teeth. All of the major bones were found but in several pieces.[3] Surprising results showed that they were dealing with a 9000 year old skeleton rather than a man of the nineteenth century, as originally thought. At the University of California at Riverside, a small piece of bone was subjected to radiocarbon dating to determine that the Kennewick Man was approximately 9,300 years old.[2] After collecting all the bone pieces, Chatters concluded the subject was a Caucasoid male about 68ﾊinches (173ﾊcm) tall who died in his mid fifties.

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