Chapter 3 Notes Atomic Theory

Atomic Theory Essential Questions 1. What are the characteristics of each of the three elementary subatomic particles? 2. How are different isotopes of elements written? 3. How are the atomic number and mass number of element abbreviated ( A Z X)?

Daltons Atomic Theory Note: write yellow parts in notes & include the orange, underlined part as a modification to the theory All matter is made up of atoms. Defined by Democritus to mean small, indestrucible, building blocks of matter, but the nuclear fission (bomb) changed this definition of atom. Atoms combine in simple, whole number ratios to create compounds.

Daltons Atomic Theory Note: write yellow parts in notes & include the orange, underlined part as a modification to the theory Atoms of the same element are identical modified when isotopes were discovered to specify that identical meant number of protons Atoms of different elements are different. modified to specify that different elements have different numbers of protons

1.All matter is composed of extremely small particles called atoms 2.Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, & other properties ELEMENT 3 ELEMENT 3 ELEMENT 1 ELEMENT 1 ELEMENT 4 ELEMENT 4 Atomic Theory ELEMENT 2 ELEMENT 2

3.Atoms cannot be subdivided, created, or destroyed 4.atoms of different elements combine in simple whole # ratios to form chem compounds 5.in chemical rxns, atoms are combined, separated, or rearranged Atomic Theory

Particles of an Atom ParticleSymbolChargeMassLocation Proton p amuNucleus Electron e - ~ 0 amuOutside nucleus Neutron n 0 01 amuNucleus

An Atom Becomes an Ion Charges of the electron and proton are used to calculate the atoms net charge. If an atom has a charge other than zero it is called an ION. Net charge = # protons - # electrons Mg has 12 protons and 12electrons as an atom. When it becomes an ion (like Neon) it has only 10 electrons. 12 p e - = +2 net charge

Net Charge Example Phosphorus (P) has 15 protons and 18 electrons as an ion. What is its net charge? 15 p e - = -3 net charge

II. Isotopes Defined as atoms with the same atomic number (or number of protons), but with different atomic mass due to change in number of neutrons. Hydrogen isotopes (look at the patterns!) 1. Protium (Hydrogen-1) 1 p, 1 e, 0 n; Mass = 1 amu 2. Deuterium (Hydrogen -2) 1 p, 1e, 1 n; Mass = 2 amu 3. Tritium (Hydrogen - 3) 1 p, 1e, 2 n; Mass = 3 amu Note: Isotopes commonly named with element name followed by isotopes mass number

Carbon Isotopes Try this example now Carbon isotopes 1. Carbon Carbon - 14 How many p, e and n does each carbon isotope have?

Carbons p, e and n totals Answer 1. Carbon - 12 has atomic number 6 so it has 6 protons and 6 electrons. Its mass is 12, so 12 - the 6 protons = 6 neutrons 6 p, 6 e, and 6 n 2. Carbon only the neutron number changes for this isotope. 6 p and 6 e and (14-6) = 8 n.

Nucleons - particles that make up the nucleus A. Protons number of protons = atomic number = # of electrons (if neutral atom) atomic number (and therefore # p) identifies an element atomic number = Z atomic numbers 1- ____ identified so far B. Neutrons = atomic mass - number of protons mass of neutron = mass of proton = 1/12 mass of C atom

Atomic Mass and Mass Number A. mass number = sum of protons and neutrons in nucleus = whole number =A B. atomic mass = average of the masses of isotopes = decimal number on the periodic table

Atomic Mass and Mass Number C. A Z X - isotope abbreviation or element name-isotope mass number X = symbol of element A = mass number Z = atomic number A - Z = number of neutrons Note: isotopes have a different A number

AZX examples Co ( Mass # written directly above atomic # ) Atomic # 27 Mass # 59 Protons 27 Electrons 27 Neutrons = = 32

AZX examples U Atomic # =92 Mass # =235 Protons =92 Electrons =92 Neutrons = = 143

Nucleus - Gold Foil Experiment Nucleus discovered by Lord Ernest Rutherford Gold Foil Experiment a.k.a. Alpha Scattering Experiment Alpha particle - positively charged helium atom released when radioactive elements decay Particles entered a closed, circular, luminescent screen and hit gold foil, which was suspended in the center of the circle

Gold Foil Conclusions Since nearly all the alpha particles passed through the foil, the atom is mostly empty space. Since some particles were deflected backwards, the atom contains a nucleus. A nucleus is a small, dense, positively- charged center of an atom.

Planetary Model of the Atom (a.k.a. Rutherford-Bohr Atom) proposed by Lord Rutherford and Niels Bohr contains a nucleus has energy levels - definite orbits in which an electron can travel Looks like sun with planets in circular orbits around it

ATOMS OF THE 1 ST TEN ATOMS NAMESYMBOL ATOMIC # MASS # p+p+p+p+ e-e-e-e- n0n0n0n0 HydrogenH11110 HeliumHe24222 LithiumLi37334 BerylliumBe49445 BoronB CarbonC NitrogenN OxygenO FluorineF NeonNe

Chapter 19 - Radioactivity Essential Questions: 1. How are nuclear decay reactions written and balanced? 2. How is half-life used to find the amount of a radioactive isotope that remains over time? 3. How do nuclear power plants make electricity?

Chapter 19 - Radioactivity I. Radioactivity - the phenomenon of rays being produced spontaneously from unstable atomic nuclei A. Three forms of natural radiation (Rutherford) 1. Alpha particle [ ] = helium nucleus ( 4 He +2 ) 2. Beta particle [ - ] = an electron ( -1 e) 3. Gamma Rays [ ] = a high energy x-ray( 0 ) B. Radioactive Decay - spontaneous emission of charged particles (radiation) resulting in the transformation of radioactive nuclei

C. Types of Nuclear Reactions 1. alpha particle emission ( ) 4 2 He 2. K electron capture (EC) 0 -1 e 3. positron emission ( + ) 0 +1 e 4. beta emission ( - ) 0 -1 e 5. neutron emission (n) 1 0 n

E. A Geiger Counter - instrument for detecting radioactive decay Study examples and do self-check exercises - p

Nuclear Decay Equations 241 Am 4 He 1.Determine the atomic number for the isotope given… Here Americium has a 95 subscript since 95 is the atomic number of Am 2. A helium atom being produced means that an alpha particle has been emitted. Its atomic number is Am 4 2 He

Decay Example #1 contd 3. To predict the products of the decay reaction we need to determine what superscript number (mass #) is needed to make the equation true Am 4 2 He since 241 – 4 = To predict the isotope that is produced we need to determine the subscript number (atomic #) using the same method Am 4 2 He since 95 – 2 = 93

Decay Example #1 Answer 5. Finally determine the elements symbol using the atomic number of the isotope and the periodic table. Here we look up #91 to find Protactinium (Pa) and fill in the symbol to complete the isotopic abbreviation and the decay equation Am 4 2 He Np

Decay Example #2 Silver-110 undergoes beta emission. Write a balance decay equation for this isotope Ag 0 -1 e + ?

Decay Example #2 Answer Ag 0 -1 e Cd Since = 110 And 47 - (-1) = 48 Since 48 is cadmiums atomic number Cd

Decay Example #3 Cobalt – 58 undergoes positron emission. Complete its decay equation. 58 Co 0 +1 e

Decay Example #3 Answer Co 0 +1 e Fe = 58 superscript 28 – 1 = 27 subscript 27 is irons atomic number Fe

Half-Life 1. HALF_LIFE -(t 1/2 ) length of time it takes for half of the atoms in a given radioactive sample to decay A. Table of Half-lives found on full color/2-sided periodic table B. Actinium-227 has a half-life = 22 y. If you start with 500 grams, how long will it take for less than one gram to remain? Time Amount Answer= 198 years or 9 half-lives

Radioactive decay curve for 500g of actinium-227 TIME ( ) ( )

III. Nuclear Transmutation or Nuclear Transformation - an atom with a different atomic number is produced as a result of a nuclear reaction A. Natural decay reactions emit only alpha particles, beta particles, and gamma rays. example: (see p. 610 decay of U-238 to Pb-206)

B. Artificial Transmutation combines an element with a radioactive particle, another element or neutron 1. earliest artificial transmutation by Rutherford in N + 4 He 17 O + 1 H 2. Synthetic elements are made from smaller elements and are produced by transmutations a. Occur in particle accelerator b. Elements with at. # > 100 are formed this way. c. 254 Es + 4 He 256 Md + 2 n 1

Use of Radioactive Nuclides A. Radiotracers - a radioactive isotope of an element being studied that is used to follow a reaction or process. See Table 19.4 p I-131 – used to study thyroid gland 2. Tl … damage to heart muscle 3. Ba - - … digestive system B. Dating objects that were once living 1. Carbon - 14 has a half life of 5730 years 2. accurate for dating once living organisms 70,000 + years old

Radioactive isotopes in common things C. Smoke Detectors contain Americium D. Fluorescent lamps contain Promethium – 147.

Nuclear Fission V. Fission - the splitting of a nucleus into 2 approximately equal parts A. releases a large amount of energy and some neutrons B. occurs when a very heavy nucleus is split. C. bombarding an element with neutrons_ makes it unstable emitted neutrons cause a chain reaction. A Critical Mass is a certain mass of fissionable material needed in order to cause a fission event. If subcritical the neutrons escape and chain reaction stops

Manhattan Project F. Manhattan Project - World War II project to build fission bombs that were dropped on Hiroshima and Nagasaki. Bombs contained 2 subcritical masses that were combined suddenly to create the explosion. G. See p. 620 Figures 19.4 and 19.5

VI. Nuclear Reactors- control nuclear fission A. reactors produce heat for electric power or propulsion units for ships & submarines B. heated water produces steam, which turns turbines C. Uranium-238 and Plutonium-239 are used as fuel for nuclear reactors D. Moderators (like water and graphite) slow down neutrons E. Control rods regulate rate of reaction by absorbing neutrons F. Breeder Reactors create fissionable Pu-239 from non-fissionable U-238; make fuel for other nuclear reactors.

VII. Fusion – combining 2 atomic nuclei into 1 A. produce much more energy than fission reactions B. doesnt produce radioactive wastes C. occurs in the sun D. combines isotopes of hydrogen to make helium E. uses water as a source of hydrogen F. fusion reactors will be created in your lifetime.