1. Unit 3: Part 2 of the Atom Nuclear Chemistry
I. The Nucleus
(p. 701 – 704 in Class Modern Chemistry Text) II
III IV

2. A. Mass Defect
Difference between the mass of an atom and the mass of its individual particles.
amu
amu

3. Important Values 1.007276 amu = mass of 1 p+
amu = mass of 1 n0
amu = mass of 1 e-
x kg = 1 amu
Speed of light (c) = 3.00 x 108 m/s

4. A. Mass Defect Calculated
Helium-4 nuclide: Atomic Mass = amu
How do we calculate its mass defect?
Find the mass of the subatomic particles 1st
2 p+ = (2 x amu) = amu
2 n0 = (2 x amu) = amu
2 e- = (2 x amu) = amu
Total combined mass = amu

5. A. Mass Defect Calculated
How do we calculate its mass defect?
Total combined mass - Atomic mass = mass defect
amu – amu = amu
The measured mass is amu less then the total mass we calculated for the combined subatomic particles
This is the mass defect for the helium-4 nuclide

6. B. Nuclear Binding Energy
Energy released when a nucleus is formed from nucleons.
High binding energy = stable nucleus.
E = mc2
E: energy (J)
m: mass defect (kg)
c: speed of light (3.00×108 m/s)

7. Converting mass defect to Nuclear Binding Energy
We will use the helium-4 nuclide again
Convert mass defect from amu to kg amu x kg amu
E = mc2 = (5.0441x10-29 kg)(3.00 x 108 m/s)2
= 4.54 x J
This is the energy required to hold the nucleus together
= x10-29 kg

8. Practice Problem
Calculate the nuclear binding energy of a sulfur-32 atom. The measured atomic mass of this nuclide is amu.
Answer = 4.36 x J

9. B. Nuclear Binding Energy
Unstable nuclides are radioactive and undergo radioactive decay.

10. Nuclear Reactions
In equations representing nuclear reactions, the total of the atomic numbers and the total of the mass numbers must be equal on both sides of the equation.
Here is an example
Br He  C n
 Notice there has been a transmutation

11. Quiz
A process in which a very heavy nucleus splits into more-stable nuclei of intermediate mass is called:
  radioactive decay
  nuclear fusion
  a chain reaction
  nuclear fission
  radiocarbon dating

12. Quiz
Very large nuclei tend to be unstable because of the:
repulsive forces between protons
attraction of protons for neutrons
repulsive forces between neutrons
attraction of electrons for the positively charged nucleus

13. Quiz Compared to chemical reactions, nuclear reactions produce:
 proportionally far less energy
 proportionally far more energy
 more vegetables
 fewer changes in the nucleus

14. Online practice quiz for you to try
Online practice quiz for you to try
Using the Modern Chemistry text try the section review questions on page 704.

15. VOCABULARY
Nucleons: the protons and neutrons in the nucleus of an atom
Nuclide: an atom in nuclear chemistry is referred to as one of these
Mass defect: the difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons
Nuclear binding energy: the energy released when a nucleus is formed from nucleons. It is calculated using E = mc2
Nuclear reaction: a reaction that changes the nucleus of an atom
transmutation: a change in the identity of a nucleus as a result of a change in the number of protons