1 NUCLEAR CHEMISTRY

2 Isotopes Same element (Z) but different mass number (A).Same element (Z) but different mass number (A). Boron-10 has 5 p and 5 n: 10 5 BBoron-10 has 5 p and 5 n: 10 5 B Boron-11 has 5 p and 6 n: 11 5 BBoron-11 has 5 p and 6 n: 11 5 B 10 B 11 B

3 Isotopes Hydrogen:Hydrogen: – 1 1 H, protium – 2 1 H, deuterium – 3 1 H, tritium (radioactive) Helium, 4 2 HeHelium, 4 2 He Lithium, 6 3 Li and 7 3 LiLithium, 6 3 Li and 7 3 Li Boron, 10 5 B and 11 5 BBoron, 10 5 B and 11 5 B Except for 1 1 H the mass number is always at least 2 x atomic number.Except for 1 1 H the mass number is always at least 2 x atomic number. Repulsive forces between protons must be moderated by neutrons.Repulsive forces between protons must be moderated by neutrons.

4 ATOMIC COMPOSITION ProtonsProtons –+ electrical charge –mass = x g –relative mass = atomic mass units (amu) ElectronsElectrons – negative electrical charge –relative mass = amu NeutronsNeutrons –no electrical charge –mass = amu

5 Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

6 Radioactivity Emission of particles and/or energy due to a change in the nucleus of an atom. Nuclear Radiation also called Ionizing radiation Measure with Geiger Counter

7 Geiger Counter: Radiation detection

8 Types of NUCLEAR Radiation

9 Nuclear Reactions Ernest Rutherford found Ra forms Rn gas when emitting an alpha particle. 1902—Rutherford and Soddy proposed radioactivity is the result of the natural change of the isotope of one element into an isotope of a different element.

10 Nuclear Reactions orTransmutations Natural Decay Spontaneous breakdown of unstable nuclei. Called Radioisotopes

11 Penetrating Ability

12 NATURAL Decay: DECAY = Fall apart Alpha DECAY Beta DECAY Positon DECAY

13 Nuclear Reactions Alpha emissionAlpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons are rearranged but conserved [mass number (A)] Nucleons = PROTON OR NEUTRON (particle in the nucleus)

14 Nuclear Reactions Beta emissionBeta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. How does this happen?

15 Other Types of Nuclear Reactions Positron ( 0 +1  ): a positive electron K-capture: K-capture: the capture of an electron from the first or K shell An electron and proton combine to form a neutron e p --> 1 0 n 207

16 Radioactive Decay Series

17 Writing Nuclear Reactions Parent element = Reactant Daughter element = Product Radioactivity = radiation produced

18 Writing Nuclear Reactions Law of Conservation of Mass L. of C. of Charge Isotopic Notation Mass # and Nuclear Charge 14 6 C = 14 7 N e

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21 Stability of Nuclei Heaviest naturally occurring non-radioactive isotope is 209 Bi with 83 protons and 126 neutrons Heaviest naturally occurring non-radioactive isotope is 209 Bi with 83 protons and 126 neutrons There are 83 x 126 = 10,458 possible isotopes. Why so few actually exist? There are 83 x 126 = 10,458 possible isotopes. Why so few actually exist?

22 Band of Stability and Radioactive Decay Am --> 4 2  Np  emission reduces Z  emission increases Z Co --> 0 -1  Ni Isotopes with low n/p ratio, below band of stability decay, by positron emission or electron capture

23 Stability of Nuclei Out of > 300 stable isotopes: Even Odd Odd Even Z N P 19 9 F 2 1 H, 6 3 Li, 10 5 B, 14 7 N, Ta

24 Binding Energy, E b E b = energy required to separate the nucleus into protons and neutrons. For deuterium, 2 1 H 2 1 H ---> 1 1 p nE b = 2.15 x 10 8 kJ/mol E b per nucleon = E b /2 nucleons = 1.08 x 10 8 kJ/mol nucleons = 1.08 x 10 8 kJ/mol nucleons

25 Binding Energy/Nucleon

26 Calculate Binding Energy For deuterium, 2 1 H: 2 1 H ---> 1 1 p n Mass of 2 1 H = g/mol Mass of proton = g/mol Mass of neutron = 1/ g/mol ∆m = g/mol From Einstein’s equation: E b = (∆m)c 2 = 2.15 x 10 8 kJ/mol E b per nucleon = E b /2 nucleons = 1.08 x 10 8 kJ/mol nucleons

27 Half-Life Section 15.4 & Screen 15.8 HALF-LIFE is the time it takes for 1/2 a sample is disappear.HALF-LIFE is the time it takes for 1/2 a sample is disappear. The rate of a nuclear transformation depends only on the “reactant” concentration.The rate of a nuclear transformation depends only on the “reactant” concentration. Concept of HALF-LIFE is especially useful for 1st order reactions.Concept of HALF-LIFE is especially useful for 1st order reactions.

28 Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?

29 Kinetics of Radioactive Decay Activity (A) = Disintegrations/time = (k)(N) where N is the number of atoms Decay is first order, and so ln (A/A o ) = -kt The half-life of radioactive decay is t 1/2 = 0.693/k