Nuclear Chemistry

“regular” chemistry involves only the ELECTRONS in atoms

All the rest of this year we will be studying only “regular” chemistry

“nuclear” chemistry involves only the NUCLEUS in atoms

In this chapter (and only this chapter) we will be studying “nuclear” chemistry

Important Reminder!

• Every atom of the same element must have the same number of PROTONS in its nucleus

• For example, for Lithium to be Lithium, it must have 3 protons. An element with only two protons would be He, with 4 protons Be

• If the number of protons in a nucleus changes, the atom becomes a different element!

Remember the alchemists?

• They wanted to change Pb (82 protons) into Au (79 protons)

• To achieve this would have meant removing 3 protons from the Pb atom’s nucleus

• Alchemists would have needed to do NUCLEAR chemistry

Stability of atoms

• All the atoms we have studied so far have been “stable”. That means they stay the same and don’t change into other atoms

• Some atoms are not stable. They tend to “decay” into other atoms.

• Unstable atoms are called RADIOISOPTOPES

Which atoms are unstable?

• The ratio of protons and neutrons in the nucleus determines an atom stability

# of n = # of p(1 to 1 ratio)

Stableatoms

All atoms with more than 83 protons are unstable

Which atoms are unstable?

• All atoms with more than 83 protons

• Some isotopes of atoms with less than 83 protons do not have the right proton to neutron ratio to be stable

Remember! An isotope is an atom with more or less neutrons than other atoms of that same element

What happens when an unstable atom “decays” ?

• It emits (gives off) radiation particles.

This means it is radioactive.

• It makes a new atom that is more stable

Types of Radiation particles

• Alpha

• Beta

• Positron

• Gamma Ray

Alpha Particles

α Greek letter alpha

It is the nucleus of a He atom (no e-)

with 2 protons, 2 neutrons and

a charge of +2

He42

Beta Particles

β or β Greek letter beta

Like an electron except it comes

out of the nucleus, not the e- cloud

has negligible (no) mass

has a charge of -1

-

Positron Particles

β Greek letter beta

has negligible (no) mass

has a charge of +1

Like an e- (or β) but with a

positive charge

+

Gamma Rays

γ Greek letter gamma

High energy particle, like x-rays

no mass

no charge

Penetrating power

When an unstable atom undergoes alpha decay…..

U23592

decays to

Th23190

Uranium-235 Thorium-231 and an alpha particle

+ He42

Parent atom Daughter product radiation

What is happening here?

Fr22087 At216

85 + He42

What is happening here?

Fr22087 At216

85 + He42

Fr-220 decays to At-216 and an alpha particle

The following unstable atoms decay by emitting an alpha particle

Ra -226

Rn- 222

Th-232

Look in Table N to find other atoms whose decay mode is also an alpha particle

Write the decay equation for:

Ra -226

Step 1: Re-write the atom symbol so it includes both atomic mass and atomic number (look it up!)

Ra22688

Atomic massAtomic number

Write the decay equation for Ra-226:

Step 2: Put the unstable atom on the left side of the decay arrow

Ra22688

Radium -226 decays to

Write the decay equation for Ra-226:

Step 3: Look up decay mode for the atom in Table N and write that after the decay arrow

Ra22688

Radium -226 decays to alpha particle

α42

Write the decay equation for Ra-226:

Step 4: Find the daughter product by conserving mass and charge

Ra22688

Radium -226 decays to alpha and atom X particle

α42 +

22286 X

226 = 4 + 222

88 = 2 + 86

Write the decay equation for Ra-226:

Step 5: Identify the daughter product by looking up its atomic number

in the periodic table

Ra22688

Radium -226 decays to alpha and Radon-222 particle

α42 +

22286 Rn

You try it for:

Radon -222

Thorium – 232

Uranium - 233