Nuclear Chemistry SS3 Chemistry Lesson Note

CONTENT

• Types and Nature of Radiation
• Half-life as a measure of the stability of the nucleus.

Nuclear Chemistry is an aspect of chemistry that deals with nuclei of atoms.

Radioactivity

This is the spontaneous emission of radiation by a radioactive element such as Thorium, Uranium etc.

Characteristics

1. Spontaneously and continuously emitting radiation by a radioactive element
2. Temperature and pressure do not affect radioactivity
3. The radiation can pass through opaque objects
4. It affects photographic plates
5. It causes the ionisation of gases through which it passes.
6. It causes fluorescence of certain substance
7. It releases a large amount of energy.

Types of Radiation

There are three (3) types of radiation

1. Alpha
2. Beta
3. Gamma

Characteristics of Alpha-rays

1. They are Helium in nature 42He with 4 atomic mass and 2 atomic number
2. Alpha rays are fast-moving streams of positively charged
3. They are deflected toward the negative plate in an electrostatic field
4. They have a very low penetrating power
5. They can be absorbed/stopped by a thin sheet of paper on Aluminium foil
6. They cause fluorescence of some materials e.g Zinc Sulphide

Characteristics of beta-rays

1. They are electron in nature with a mass number of zero and charge of -1 (°e)
2. They are a fast-moving stream of electrons
3. They can penetrate than alpha rays

Evaluation

1. State two (2) properties of ά, β, and Y rays each.
2. What do you know about radioactivity?

Detection of radiation

The radiation can be detected by using the following devices.

1. Geiger Miller Counts
2. Scintillation counter
3. Diffusion cloud chamber

Half-life

The half-life of a radioactive element is the time taken for half of the actual number of atoms in a given substance or radioactive element to decay.

Nuclear stability

The spontaneous disintegration/decay of the nucleus of an element is due to its instability. The neutron-proton ratio determines the stability of an element.

This varies between unity for the lighter elements and a value of about 1.5 for the heavier element with atomic numbers around eighty.

N.B. Atoms with neutrons – protons less than 1 or greater than 1.5 tend to be unstable.

Evaluation

1. State two methods through which radiation can be detected.
2. What is half-life as a measure of the stability of the nucleus?

General Evaluation

1. Define the term nuclear chemistry
2. Define the term radioactivity.
3. Explain the term radioisotopes
4. Give an account of the uses of radioisotopes.

Reading assignment

• New School Chemistry by O.Y, Ababio pages 299-304.

Weekend Assignment

1. _______is an example of radiation (a) Aloha (b) Carbon (c) Uranium (d) Nucleus.
2. Alpha particle was deflected towards the negative plate while Beta deflected toward (a) Neutral plate (b) Negative plate (c) Zero plate (d) positive plate
3. The following caused fluorescence of matter except for (a) Alpha (b) Beta (c) Gamma (d) X-ray
4. In the above diagram, Z represents (a) Alpha (b) Beta (c) Gamma (d) Radioactive

Theory

1. Find the half-life of a radioisotope element which was found to be 120g initially and later changed to 15g in 24 hours
2. State the three main types of radiation with their properties each.