1. Unit 4: Periodicity and Nuclear Chemistry
C.5.C use the Periodic Table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energy
C.12.A describe the characteristics of alpha, beta, and gamma radiation
C.12.B describe radioactive decay process in terms of balanced nuclear equations
C.12.C compare fission and fusion reactions

2. Table of Contents Periodicity 3-17 Nuclear Chemistry I
Types of Radiation and Nuclear formulas 18-29
Nuclear Chemistry II
Nuclear Fission and Fusion & Half-Life

3. Periodicity
Periodic Trends

4. Periodic Law
The chemical and physical properties of the elements are periodic functions of their atomic numbers; properties of the elements occurred at repeated intervals called periods.
This defines the property of periodicity

5. Periodic Trends
properties that show patterns when examined across the periods or vertically down the groups
while there are many periodic trends, we will focus on
atomic radii (the plural of radius)
ionization energy
Electronegativity
Ionic radii (the plural of radius)

6. Atomic Radii
One half the distance between the nuclei of identical atoms that are bonded together.
Distance between nuclei decreases across periods because the higher nuclear charge (positive) pulls the electrons closer to the nucleus
increases down groups because energy levels are being added outside the nucleus

7. Atomic Radii Decreases
Atomic Radii Increases

8. Graphing Atomic radii
The graph of Atomic Radius vs. Atomic Number shows the trend in atomic radius as one proceeds through the first 37 elements in the periodic table.

9. Ionization Energy
The energy required to remove one electron from a neutral atom of an element.
increases across periods because it takes more energy to overcome the electrons attraction to the increasing nuclear charge
decreases down groups because it is easier to overcome the nuclear charge for the outermost electrons as the number of energy levels increases

11. Graphing Ionization Energy
These trends are visible in the graph of ionization energy versus atomic number.

12. Electronegativity
a measure of the ability of an atom in a compound to attract electrons from other atoms
increases across periods as a result of the increasing nuclear charge and ability of the nucleus to attract electrons from a neighboring atom
decreases down groups because the nuclear charge is less able to attract electrons from another atom as additional energy levels are added

14. Graphing Electronegativity
The graph of Electronegativity vs. Atomic Number shows the trend in the electronegativity as one proceeds through the first 37 elements in the periodic table.

15. Ionic Radii
The radius of an atom forming ionic bond or an ion. The radius of each atom in an ionic bond will be different than that in a covalent bond.
The reason for the variability in radius is due to the fact that the atoms in an ionic bond are of greatly different size. One of the atoms is a cation, which is smaller in size, and the other atom is an anion which is a lot larger in size.

16. decreases across the period until formation of the negative ions then there is a sudden increase followed by a steady decrease to the end
The sudden increase on formation of negative ions is due to the new (larger) outer shell

17. Graphing ionic radii

18. I. Types of radiation & Nuclear formulas
Nuclear Chemistry
I. Types of radiation & Nuclear formulas

19. Introduction to Nuclear Chemistry
Nuclear Reactions
Nuclear chemistry is the study of the structure of atomic nuclei and the nuclear change they undergo.
Characteristics:
Isotopes of one element are changed into isotopes of another element
Contents of the nucleus change
Large amounts of energy are released

20. Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles and/or rays
Atoms remain unchanged, although they may be rearranged
Atoms often converted into atoms of another element
Involve only valence electrons
May involve protons, neutrons, and electrons
Associated with small energy changes
Associated with large energy changes
Reaction rate influenced by temperature, particle size, concentration, etc.
Reaction rate is not influenced by temperature, particle size, concentration, etc.

21. mass # atomic # neutrons atomic # mass #
Chemical Symbols
A chemical symbol looks like…
To find the number of , subtract the
from the
mass # 14 C
atomic # 6
neutrons
atomic #
mass #

22. Types of Radiation
Radioactive Decay – when unstable nuclei lose energy by emitting radiation to attain more stable atomic configurations (spontaneous process)
Alpha – radioactive decay of an atomic nucleus that is accompanied by the emission of an alpha particle( ).
Beta – Radioactive decay in which an electron is emitted ( ).
Gamma – High energy photons that are emitted by radioactive nuclei.

23. Alpha Decay
Alpha decay – emission of an alpha particle (α), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is +2 because of the 2 protons
Alpha decay causes the mass number to decrease by 4 and the atomic number to decrease by 2.
Atomic number determines the element. All nuclear equations are balanced. 4 He 2

24. Alpha Decay
Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission.
Step 3: Write the alpha particle.
Step 4: Determine the other product (ensuring everything is balanced).
Step 2: Draw the arrow.
Step 1: Write the element that you are starting with.
Mass #
210 Po 84
206 Pb 4 He 2 82
Atomic #

25. Beta decay
Beta decay – emission of a beta particle (β), a fast moving electron, denoted by the symbol e- or β has insignificant mass (0) and the charge is -1 because it’s an electron.
Beta decay causes no change in mass number and causes the atomic number to increase by 1.

26. C e N Beta Decay 14 6 14 -1 7 Step 3: Write the beta particle.
Example : Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission.
Step 3: Write the beta particle.
Step 4: Determine the other product (ensuring everything is balanced).
Step 2: Draw the arrow.
Step 1: Write the element that you are starting with.
Mass # 14 C 6 14 e -1 N 7
Atomic #

27. Gamma decay
Gamma rays – high-energy electromagnetic radiation, denoted by the symbol γ.
γ has no mass (0) and no charge (0). Thus, it causes no change in mass or atomic numbers.
Gamma rays almost always accompany alpha and beta radiation.
However, since there is no effect on mass number or atomic number, they are usually omitted from nuclear equations.
Example: ϒ +

28. Penetration of Radiation
Alpha and beta are particles emitted from an atom.  Gamma radiation is short-wavelength electromagnetic waves (photons) emitted from atoms.
The figures show the penetration of the different types of radiation.

29. Type of Radioactive Decay
Review
Type of Radioactive Decay
Particle Emitted
Change in Mass #
Change in Atomic #
Alpha
α He -4 -2
Beta
β e +1
Gamma γ 4 2 -1

30. II. Nuclear Fission and Fusion & Half Life
Nuclear Chemistry
II. Nuclear Fission and Fusion & Half Life

31. Nuclear Fission Fission - splitting of a nucleus.
- Very heavy nucleus is split into two approximately equal fragments.
-Chain reaction releases several neutrons which split more nuclei.
- If controlled, energy is released slowly
(like in nuclear reactors). Reaction control depends on reducing the speed of the neutrons (increases the reaction rate) and absorbing extra neutrons (decreases the reaction rate).

32. Nuclear Fission - Examples – atomic bomb, current nuclear power plants
→ x 102 kJ/mol

33. Nuclear Fusion Fusion - combining of a nuclei
Two light nuclei combine to form a single heavier nucleus
- Does not occur under standard conditions (+ repels +)
- Advantages compared to fission
Inexpensive, No radioactive waste
- Disadvantages
requires large amount of energy to start, difficult to control

34. Nuclear Fusion
Examples – energy output of stars, hydrogen bomb, future nuclear power plants

35. Half-Life
Half Life is the time required for half of a radioisotope’s nuclei to decay into its products.
For any radioisotope,
# of ½ lives
% Remaining
100% 1
50% 2
25% 3
12.5% 4
6.25% 5
3.125% 6
1.5625%

36. Half-Life
For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years?  
You can use a table:
# of ½ lives
Time (Years)
Amount Remaining (g) 10 1 29 5 2 58
2.5 3 87
1.25 4
116
0.625

37. initial mass mt = m0 x (0.5)n mass remaining # of half-lives
Half-Life
Or an equation!
initial mass
mt = m0 x (0.5)n
mass remaining
# of half-lives

38. Half-Life
Example 1: If gallium – 68 has a half-life of minutes, how much of a mg sample is left after 1 half life? ________
2 half lives? __________ 3 half lives? __________

39. Half-Life
Example 1: If gallium – 68 has a half-life of minutes, how much of a mg sample is left after 1 half life? ________
mt = mg x (0.5)1 = 80.0 mg
2 half lives? __________
mt = mg x (0.5)2 = 40.0 mg
3 half lives? __________
mt = mg x (0.5)3 = 20.0 mg

40. Half Life
Iodine-131 is a radioactive isotope with a half-life of 8 days. How many grams of a 64 g sample of iodine-131 will remain at the end of 8 days? ________
How many grams of a 64 g sample of iodine-131 will remain at the end of 24 days? ________

41. Half Life
Iodine-131 is a radioactive isotope with a half-life of 8 days. How many grams of a 64 g sample of iodine-131 will remain at the end of 8 days? ________
Mt = 64 g x (0.5)1 = 32 g
How many grams of a 64 g sample of iodine-131 will remain at the end of 32 days? ________
First how many ½ lives have gone by.
32/8 (the ½ of iodine-131) = 4
Then plug 4 into formula.
Mt = 64 g x (0.5)4 = 4 g