Hydrogen-1 Contains 1 proton and 1 electron – as all isotopes of H must contain. No neutrons The most common type of H atom.

Hydrogen-2, deuterium Contains 1 proton and 1 neutron in the nucleus.

Hydrogen-3, tritium Contains 1 proton and 2 neutrons in the nucleus.

LecturePLUS Timberlake
Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl chlorine chlorine - 37 LecturePLUS Timberlake

Isotopes Nucleus Neutron Proton + Electrons Nucleus Nucleus Neutron Proton + Carbon-12 Neutrons 6 Protons 6 Electrons 6 Electrons The chemistry of each element is determined by its number of protons and electrons. In a neutral atom, the number of electrons equals the number of protons. Symbols for elements are derived directly from the element’s name. Nuclei of atoms contain neutrons as well as protons. The number of neutrons is not fixed for most elements, unlike protons. Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes. Isotopes have same numbers of protons and electrons but have different NEUTRONS. Carbon-14 Neutrons 8 Protons 6 Electrons 6 Nucleus

Learning Check AT 2 Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C C 14C #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______ LecturePLUS Timberlake

Solution AT 2 12C C 14C #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ _ 6___ ___6___ LecturePLUS Timberlake

Learning Check AT 3 An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) ) ) 65 B. Number of neutrons in the zinc atom C. What is the mass number of a zinc isotope with 37 neutrons? 1) ) ) 67 LecturePLUS Timberlake

Solution AT 3 An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) 30 B. Number of neutrons in the zinc atom 2) 35 C. What is the mass number of a zinc isotope with 37 neutrons? 3) 67 LecturePLUS Timberlake

Learning Check AT 5 An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) ) ) 34 B. Its mass number is C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34X 2) 34X 3) 36X LecturePLUS Timberlake

Solution AT 5 An atom has 14 protons and 20 neutrons. A. It has atomic number 1) 14 B. It has a mass number of 3) 34 C. The element is 1) Si D. Another isotope of this element would be 3) 36X 14 LecturePLUS Timberlake

6Li 7Li 3 p+ 3 n0 3 p+ 4 n0 2e– 1e– 2e– 1e– + + Lithium-6 Lithium-7
Nucleus Neutron Proton Nucleus Neutron Proton Electrons + Electrons + Nucleus Nucleus Lithium-6 Lithium-7 Neutrons 3 Protons 3 Electrons 3 Neutrons 4 Protons 3 Electrons 3

Calculating Atomic Mass
Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope1(%) + mass isotope2(%) + … LecturePLUS Timberlake

Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu % 25Mg = amu % 26Mg = amu % Atomic mass (average mass) Mg = 24.3 amu Mg 24.3 LecturePLUS Timberlake

Learning Check AT7 Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium? LecturePLUS Timberlake

Solution AT7 Ga-69 68.9 amu x = amu for 69Ga 100 Ga-71 (%/100) 70.9 amu x = amu for 71Ga Atomic mass Ga = amu LecturePLUS Timberlake

In a sample of carbon, there is 98. 93% of carbon12 (12
In a sample of carbon, there is 98.93% of carbon12 ( amu) atoms and 1.07% of carbon13 ( amu) atoms. What is the atomic mass of carbon?

Finding An Isotopic Mass
A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope? LecturePLUS Timberlake

Assign X and Y values: X = % 10B Y = % 11B Determine Y in terms of X X Y = 100 Y = X Solve for X: X (10.0) (100 - X )(11.0) = Multiply through by 100 10.0 X X = LecturePLUS Timberlake

Collect X terms 10.0 X X = - 1.0 X = -20 X = = % 10B - 1.0 Y = X % 11B = % = 80% 11B LecturePLUS Timberlake

Learning Check AT8 Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass) 1) 30% 2) 70% 3) 100% LecturePLUS Timberlake

Solution AT8 2) 70% Solution 62.9X = 64.9X = 6350 -2.0 X = -140 X = 70% LecturePLUS Timberlake

Average Atomic Mass Avg. (mass)(%) + (mass)(%) Atomic Mass 100
weighted average of all isotopes on the Periodic Table round to 2 decimal places Avg. Atomic Mass (mass)(%) + (mass)(%) = 100 Courtesy Christy Johannesson

Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. Avg. Atomic Mass (16)(99.76) + (17)(0.04) + (18)(0.20) 16.00 amu = = 100 Courtesy Christy Johannesson

Average Atomic Mass (35)(8) + (37)(2) 10 Avg. Atomic = = Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. Avg. Atomic Mass (35)(8) + (37)(2) = = 35.40 amu 10 Courtesy Christy Johannesson

Cl 17 100 Mass spectrum of chlorine. Elemental chlorine (Cl2) contains only two isotopes: amu (75.53%) and (24.47%) 90 80 Cl-35 70 AAM = (34.97 amu)(0.7553) + (36.97 amu)(0.2447) 60 AAM = ( amu) ( amu) AAM = amu 50 Abundance 40 30 Cl-37 Mass spectrum of chlorine. Elemental chlorine (Cl2) contains only two isotopes: amu (75.53%) and (24.47%) 20 10 34 35 36 37 Mass

Mass Spectrophotometer
magnetic field heaviest ions stream of ions of different masses lightest ions electron beam gas Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 138

Weighing atoms . gas sample enters here filament current ionizes the gas ions accelerate towards charged slit magnetic field deflects lightest ions most ions separated by mass expose film The first mass spectrograph was built in 1919 by F. W. Aston, who received the 1922 Nobel Prize for this accomplishment mass spectrometry is used to experimentally determine isotopic masses and abundances interpreting mass spectra average atomic weights - computed from isotopic masses and abundances - significant figures of tabulated atomic weights gives some idea of natural variation in isotopic abundances Copyright © by Fred Senese

Mass Spectrophotometer
Magnet Negative grid Heated filament (-) (-) Detector Electron beam Neon gas inlet (+) To vacuum pump Mass numbers Evacuated glass tube Image Copyrighted by Houghton Mifflin Company

Mass Spectrometer Gives a ratio of the masses to each other that can be multiplied by the amu’s to get the atomic mass.

Mass Spectrometry - + Mass spectrum of mercury vapor
Mass spectrum of mercury vapor Photographic plate A gaseous sample is ionized by bombarding it with electrons in the lower part of the apparatus (not shown), producing positive ions. The ions pass through an electric field in which they are brought to a particular velocity. The ions then pass through a narrow slit into a curved chamber. A magnetic field is applied perpendicular to the beam of ions. All the ions with the same mass-to-charge ratio are deflected into the same circular path. (In most cases, the ionic charge is 1+ and the mass-to-charge ratio is the same as the mass.) Modern spectrophotometers use electronic detection devices (TOF = time of flight detectors) rather than photographic plates or film to establish mass-to-charge ratios and relative number of ions. - + Stream of positive ions Hill, Petrucci, General Chemistry An Integrated Approach 1999, page 320

Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart: Element Symbol Atomic Number Mass # of protons # of neutron # of electron charge 8 Potassium 39 +1 Br 45 -1 30 35 Atomic Number = Number of Protons Number of Protons + Number of Neutrons = Atomic Mass Atom (no charge) : Protons = Electrons Ion (cation) : Protons > Electrons Ion (anion) : Electrons > Protons

Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart: A N S W E R K E Y Element Symbol Atomic Number Mass # of protons # of neutron # of electron charge 8 Potassium 39 +1 Br 45 -1 30 35 Oxygen O 8 16 K 19 19 20 18 Bromine 35 80 35 36 Zinc Zn 30 65 Atomic Number = Number of Protons Number of Protons + Number of Neutrons = Atomic Mass Atom (no charge) : Protons = Electrons Ion (cation) : Protons > Electrons Ion (anion) : Electrons > Protons

Atomic Mass Magnesium has three isotopes % magnesium 24 with a mass of amu, 10.00% magnesium 25 with a mass of amu, and the rest magnesium 26 with a mass of amu. What is the atomic mass of magnesium? If not told otherwise, the mass of the isotope is the mass number in amu. Isotope Percent Abundance Mass Mg-24 78.99 Mg-25 10.00 Mg-26 Atomic mass is not a whole number because it is an average. This is why their are the decimal numbers on the periodic table. 11.01 amu California WEB

Atomic Mass Calculate the atomic mass of copper if copper has two isotopes % has a mass of amu and the rest has a mass of amu. Isotope Percent Abundance Mass Cu-63 69.1 62.93 Cu-65 64.93 30.9 63.548 Cu 29 63.548

How can we figure out how long something is dead?

Understanding Carbon-14 Dating
It’s really not that difficult

The Atom Nucleus Electron Fundamental unit of matter
Made up of components called subatomic particles Proton (positive charge) Neutron (no electrical charge) Electron (negative charge) Nucleus Electron

What Is Carbon? Types of carbon (isotopes) Atomic mass C Atomic number
Carbon-14 is also referred to as: C-14 Radiocarbon Types of carbon (isotopes) C 14 6 9 16 Atomic mass Atomic number

Unstable Isotopes (Atoms)
An atom is generally stable if the number of protons equals the number of neutrons in the nucleus Atom (Isotope) Protons Neutrons Stable Carbon 6 Stable Nitrogen 7 Stable Oxygen 8 Carbon 14 6 8

Losing Your Identity: Radioactive Decay
The nucleus of an atom (decays) changes into a new element The proton number (atomic number) changes C N 14 6 7 The nuclei of most familiar substances are stable. They retain their identies How long does this take?

Carbon-14 and Half-Life? The rate of decay is measured by how long it takes for half an element to decay (half-life) The half-life of C-14 is 5,730 years

Half-Life Illustration
5,730 years 1 half-life N-14 C-14 11,460 years 2 half-lives N-14 C-14 Time = 0 C-14 1/2 3/4 1/2 If C-14 is constantly decaying, will we run out of C-14 in the atmosphere?

How Carbon-14 Is Produced
Cosmic Rays (radiation) C-14 combines with oxygen to form carbon dioxide (CO2) Forms C-14 Collision with atmosphere (N14)

Remember… Ordinary carbon (C-12) is found in the carbon dioxide (CO2) in the air, which is taken up by plants, which in turn are eaten by animals. A bone, or a leaf or a tree, or even a piece of wooden furniture, contains carbon. When the C-14 has been formed, like ordinary carbon (C-12), it combines with oxygen to give carbon dioxide (14CO2), and so it also gets cycled through the cells of plants and animals.

We can take a sample of air, count how many C-12 atoms there are for every C-14 atom, and calculate the C-14/C-12 ratio. Because C-14 is so well mixed up with C-12, we expect to find that this ratio is the same if we sample a leaf from a tree, or a part of the body.

Carbon-14 Life Cycle N C N Cosmic radiation 14 7 14 6 14 7
Carbon-14 is produced in the atmosphere Carbon-14 decays into Nitrogen-14

How the carbon clocks works
Review There are different types of carbon There are stable and unstable atoms (isotopes) Radioactive decay Half-life (Carbon-14 = 5,730 years) C-14 life-cycle (N C N-14) Next Topics Equilibrium How the carbon clocks works

How the Carbon Dating Clock Works
Once a plant or animal dies the clock starts The plant or animal no longer takes in C-14 The C-14 present in the plant or animal begins to decay No more C-14 intake C-14 continues to decay

In living things, although 14C atoms are constantly changing back to 14N, they are still exchanging carbon with their surroundings, so the mixture remains about the same as in the atmosphere. However, as soon as a plant or animal dies, the 14C atoms which decay are no longer replaced, so the amount of 14C in that once-living thing decreases as time goes on. In other words, the 14C/12C ratio gets smaller.

When Does the Clock Start?
Once a plant or animal dies the clock starts Organism dies No more C-14 intake C-14 continues to decay

How the Carbon Clock Works
The C-14 dating method relies on measuring the amount of C-14 in the fossil Three Scenarios There is a lot of C-14 remaining in the fossil There is very little C-14 remaining in the fossil There is no detectable C-14 in the fossil

Two Things We Need to Know
What do we need to know to determine how many half-lives have expired? How fast it decays (measured in half-lives). This is known (5,730 years). The starting amount of C-14 in the fossil. A Critical Detail

Determining the Starting Amount
There are two types of carbon used in the dating process: C-12 and C-14 C-12 is a stable isotope (it does not decay) When an organism is alive it has the same ratio (C-12 to C-14) that is found in the atmosphere (1-trillion to 1) Same ratio I’m alive Different ratio I’m a fossil

Determining the Starting Amount
C-12 C-14 Amount constant Moment of death C-12 Amount constant “Infinite” age No measurable C-14 C-12 C-14 Amount constant Old

Isotopes Research Project
Isotopes in nutrition Medical Isotopes used in diagnosis Medical Isotopes used in treatment of disease Isotopic Labelling in Chemical Reactions Isotopes in Pest Control Isotopes used in agriculture Isotopes in climatology and geology Isotopes in nuclear weapons testing Isotopes in smoke alarms Isotopes in biological tracking

In addition you must also include:
What is an isotope? What is the difference between a stable and unstable isotope? What is mean by the natural abundance of isotopes? Explain how to calculate the atomic mass of an element containing a mixture of isotopes.

Hydrogen-1 Contains 1 proton and 1 electron – as all isotopes of H must contain. No neutrons The most common type of H atom.

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Hydrogen-1 Contains 1 proton and 1 electron – as all isotopes of H must contain. No neutrons The most common type of H atom.

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Presentation on theme: "Hydrogen-1 Contains 1 proton and 1 electron – as all isotopes of H must contain. No neutrons The most common type of H atom."— Presentation transcript:

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