Unit 2 Review

Elements

• Isotope: element name - mass number

• Nuclear symbol: Mass / atomic number - nuclear symbol

• Protons: Always atomic number

• Electrons: Always the same # as protons

• Neutrons: Mass - atomic

• Nuclear decay reactions

• Alpha decay - M-4 A - 2 + 4/2 He

• Beta decay - M + 0 A+1 + O/-1 e or b

• Gamma emission - M and A stay the same + 0/0 y

• Electron capture - 1/1 p + 0/-1e > 1/0 xray photon

Radiation association

• Alpha - a symbol

• Alpha blocked by paper

• Alpha - does not go through aluminum

• Alpha - has a helium nucleus

• Beta - high speed electron

• Beta - a neutron becomes a proton

• Gamma rays - high-frequency waves

• Gamma - does not cause transmutation

Half-Life

• T ½ - half-life of isotope

• #T ½ - # of half-lives (# cuts in half)

• T - time elapsed

• Mo - original mass

• Mf - final mass

How many half-lives (how many times divided in half)

Given - total time or how old (T) and Half-life of isotope (T ½)

Formula T ½ = T /T ½

Ex.

Iodine-131 has a half-life of 8 days/ How many half-lives have passed after 32 days?

T ½ = 32 days/ 8 days = 4

Nuclear energy reactions

• E = mc² (c is the speed of light, 3.0 ×10^8 m/s)

• Steps for solving

1. Determine mass loss (subtract all masses)

2. Convert energy in J to Kg ( M =1Kg /1000g)

3. Use the formula E=mc² (substitute)

4. Convert energy in J to Kj

Fission vs Fusion

Fission - Splits an atom into 2 smaller atoms

• Used as an energy source

• Used in atomic bomb

• Generates electricity

Fusion - Two small nuclei combine to make a new, more massive nucleus

• Cannot be used for energy sources; needs a significant amount of heat

• Powers the sun and stars

• Used for power plants

• More energy is created than fission (3-10 times)

BOTH -

• Used for military weapons

• Nuclear energy