Nuclear Chemistry

Radioactivity

• The result of an unstable nucleus

• Three main types– Alpha– Beta– Gamma

Alpha

A helium atomCan result when the nucleus of a large atom

breaks apart.

23892U 234

90Th + 42He

Note that all mass is conserved.238 = 234 + 4

Beta

A high speed electron

A neutron breaks into a proton, changing the number of protons in the nucleus and resulting in a atom of a different element, and an electron that is expelled from the nucleus.

21884Po 218

85At + 0-1e

Mass of atom stays the same.

Gamma Radiation

Gamma ray – photon of light

Emitted when an atom that has released a beta particle “settles” down.

Table of types of Radiation

Half Life

Radioactive decay occurs one atom at a time

Half life is the time requires for half of the atoms that were in the starting sample to decay.

Half life is a constant rate14C – half life around 5700 yrs

Example

Start: 100 g 14C

After 5730 yrs, have 100g/2 = 50g 14C

After another 5730 yrs,

have 50g/2 = 25g 14C

After the next 5730 yrs,

have 25g/2 = 12.5g 14C

14C

Nuclear Fission

Fission – the breaking apart of an atom into smaller parts

Method – neutron “hits” a nucleus of an atom. Energy of collision is transferred to the nucleus. If sufficient, the nucleus breaks into smaller pieces creating two new atoms of other elements.

Mass is conserved.

Example

Manhattan Project

New Mexico - Los Alamos, White Sands

First nuclear bombs

Little Boy – used “critical” mass

Fat Man – conventional explosives compress atoms which then “explode”

Fusion

The Power of the Stars

Small nuclei are fused together to form larger nuclei.

Uses

Nuclear energy- Fission produces MORE radioactive

material than is consumed- Fusion produces massive amounts of

energy and smaller amounts of radioactivity. Not yet available to use on Earth.

- Medicine- Dating/determining ages of things