1. II. The Nucleus of the Atom

2. What makes up the nucleus of an atom? A. Compostion (Nucleons) 1. Protons a. Mass 1.0073 universal mass units b. Indicated by an atom’s atomic number c. Charge = +1.6 x 10 -19 Coulomb

3. A. Compostion (Nucleons) 2. Neutrons a. Mass 1.0087 universal mass units b. No charge

4. B. Universal Mass Unit 1. describes the mass of an atom 2. defined as 1/12 the mass of a carbon-12 atom. This is used because when you actually talk about the mass of an atom in kilograms is so small it does not make much sense.

5. How does the nucleus stay together? C. The Strong Nuclear Force 1. The attractive force that keeps the nucleons together, responsible for stability of the nucleus. 2. Overcomes the repulsive electrostatic force between protons 3. Strength of the strong force grows much weaker as distance between particles increases.

6. D. Mass-Energy Relationship 1. Einstein showed that mass and energy are different forms of the same thing. 2. E = mc 2 How many Joules of energy would be formed from the complete annihilation of 1 kg of mass? E = 9.00 x 10 16 J In eV? E =

7. Mass-Energy Relationship 3. When we do calculations of atoms we usually use atomic mass units (u). 4. Einstein’s formula uses mass in kg. 5. If you want to convert u to energy use the following conversion: 1 u = 931 MeV

8. E. Binding Energy 1. Total mass of nucleus is always less than the sum of masses of individual parts Ex) 4 He is composed of 2 protons & 2 neutrons Determine the mass of individual parts Sum of parts = 4.0320 u Actual mass = 4.0016u

9. E. Binding Energy 2. The difference in mass (mass defect) is converted to energy known as the binding energy - Equal to the amt of energy needed to break the nucleus into separate protons and neutrons 3. In order to determine the binding energy of a nucleus: Calculate the mass defect of the helium nucleus. 0.0304 u Convert this mass to energy using equality from reference tables. (0.0304u)(931 MeV/u) = 28.3 MeV 4. Stable nuclei must have less mass than the mass of separate pieces

10. F. Radioactive Decay 1. Discovered by Henri Becquerel 1896 2. Types of radiation found and defined by Ernest Rutherford 1899

11. 3. Alpha Decay a. Emission of an alpha particle ( 4 He) during nuclear decay b. Strong nuclear force cannot hold together large nuclei c. Element changes its identity (mass decreases, atomic number decreases) 238 U → 4 He + 234 Th

12. 4. Beta Decay a. Beta particles are high speed electrons emitted from the nucleus of atom w/ too many neutrons b. Nucleus loses small amount of nuclear mass c. Neutron decays into a proton, electron, and neutrino (proposed by Wolfgang Pauli 1930) 234 Th → 0 e + 234 Pa + 0  gamma radiation