Radioactive decay reveiw

Chemical vs Nuclear Reactions

Science Park HS -- Honors Chemistry

What do we mean by Radioactivity?

Radioactive decay: process in which an
unstable atomic nucleus loses energy by
emitting radiation in the form of particles or
electromagnetic waves.

The general idea:An unstable nucleus releases
energy to become more stable.

New elements
can form from

radioactive decay

• All of the actinides are radioactive
• All beyond Uranium (92) are man made (synthetic)

When an unstable nucleus decays, it can produce any of these particles or
forms of radiation:

´ An alpha particle

´ A beta particle

´ A gamma rays

´ Neutron

´ Positron

Most

Ionization ability
Ionizing radiation: carries enough energy to cause other
atoms to lose electrons.

Alpha particles – very ionizing
Beta particles – moderately ionizing
Gamma rays – weakly ionizing

3 Main Types of Radiation

Natural Radioactive Decay
Alpha Decay (a)

Alpha decay can most simply be described like this:

1) The nucleus of an atom splits into two parts.

2) One of these parts (the alpha particle) goes

zooming off into space.

3) The nucleus left behind has its atomic number

reduced by 2 and its mass number reduced by 4

(that is, by 2 protons and 2 neutrons).

Uranium

Thorium + alpha particle

Beta Decay (b)

1.) A neutron inside the nucleus of an atom breaks down, changing
into a proton.

2) It emits an electron which go zooming off into space.

3) The atomic number goes UP by one and mass number remains
unchanged.

4) The nuclide that decays is the one on the left-hand side of the
equation.

5) The order of the nuclides on the right-hand side can be in any
order.

Thorium

Protactinium + Electron

Gamma Decay (g)

1.)During gamma decay and unstable nucleus, releases a photon,

!
!g, because both the mass number and photon charge are 0,
photons do not change the atomic number or the mass number of
the original isotope.

Tellurium à Photon + Tellurium

Positron Emission

´ A related radioactive decay process that

is sometimes classified as beta plus
radiation is positron emission. In this
process, a proton in an unstable nucleus
changes to a neutron and releases a
positively charged electron. A positron
is represented by the notation

Science Park HS -- Honors Chemistry

Some Key Definitions Before We Move on

Mass Number=Number of Protons +
Number of Neutrons

Atomic Number= Number of Protons

Na-23
MASS #

Nuclear Equations- Alpha decay

Radium-222 undergoes alpha decay,

meaning that an alpha particle is

emitted. In addition, Rn-218 is produced.

Nuclear Equations- Beta decay

Carbon-12 undergoes beta decay, so
a beta particle is emitted. In addition,

N-14 is formed

´All the

and

on both sides ADD UP TO THE

SAME VALUE

Balancing Nuclear Equations

Decay short cuts

Decay

Change to Mass number

Change to Atomic number

Alpha

-4

-2

Beta

0

+1

Gamma

0

0

Positron

0

-1