Radioactive decay reveiw

Lesson 14:

Introduction to Nuclear Chemistry

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Author is licensed under
CC BY-SA

This Photo by Unknown Author is licensed under CC BY-SA

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

Multiple Choice

What is the strongest particle in terms of penetrating ability?

• Alpha

• Gamma

• Beta

Multiple Choice

Only can be stopped by several cm of lead or concrete

• Alpha

• Gamma

• Beta

Multiple Choice

Has no mass or charge

• Alpha

• Gamma

• Beta

Multiple Choice

Can be stopped by a sheet of paper

• Alpha

• Gamma

• Beta

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

Multiple Choice

Whats the easiest way to tell if there has been an alpha decay?

• No change at all to mass or atomic numbers

• Atomic number goes up by 1

• Change to both atomic number and mass number

• Atomic number goes down by 1

Multiple Choice

Is the electron positive or negative in a beta decay?

• Positive

• Negative

Multiple Choice

What happens to the original element when beta decay occurs?

• Atomic number goes up by 1

• Mass number goes down by 4 and the Atomic number goes down by 2

• Atomic number goes down by 1

• No change

Multiple Choice

What happens to the original element when gamma decay occurs?

• Atomic number goes up by 1

• Mass number goes down by 4 and the Atomic number goes down by 2

• Atomic number goes down by 1

• No change

Multiple Choice

What happens to the original element when positron emission occurs?

• Atomic number goes up by 1

• Mass number goes down by 4 and the Atomic number goes down by 2

• Atomic number goes down by 1

• No change

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

Multiple Choice

What is emitted?

• Beta

• Alpha

• Positron

• Betta

Multiple Choice

What is emitted?

• Beta

• Alpha

• Positron

• Gamma

Multiple Choice

What is emitted?

• Beta

• Alpha

• Positron

• Gamma

Multiple Choice

What is emitted?

• Beta

• Alpha

• Positron

• Gamma

Multiple Choice

What are the products of the following alpha decay?

Multiple Choice

What are the products of the following alpha decay?

Multiple Choice

What are the products of the following alpha decay?

Multiple Choice

What are the products of the following alpha decay?

Multiple Choice

What are the products of the following alpha decay?

Multiple Choice

What is the alpha decay of Pa-231?

• Fr-227

• Fr-235

• Pa-231

Multiple Choice

What is the beta decay of $$C_6^{14}$$

• $$N_7^{14}$$

• $$B_5^{14}$$

Multiple Choice

What is the positron emission of $$K_{19}^{40}$$

• $$Ca_{20}^{40}$$

• $$Ar_{18}^{40}$$