Unit 3 - Nuclear Chemistry

Question 1

Most atoms have a stable nucleus which doesn’t change.

However, some isotopes (radioisotopes) are unstable and undergo changes in the nuclei?

What is this called?

Answer 1

Radioactive decay

Question 2

Radioactive elements can become stable by giving out which 3 types of radiation?

Answer 2

Alpha, beta and gamma

Question 3

What are the electrical charges of Alpha, Beta and Gamma radiation?

(Positive, no charge or negative)

Answer 3

Alpha-Positive

Beta-Negative

Gamma-No charge

Question 4

Radiation can penetrate objects of different thicknesses.

Which is the most and least penetrating radiation?

Answer 4

Alpha is least penetrating.

Gamma is most penetrating.

Question 5

State what happens to the mass and atomic numbers when Thorium 232 loses an alpha particle.

Answer 5

Mass number decreases by 4
232 - 4 = 228

Atomic number decreases by 2
90 - 2 = 88

Question 6

What is meant by the half-life of a radioisotope?

Answer 6

The half-life of a radioisotope is the time taken for the sample’s activity to fall by half

or

Half-life is the time for half of the nuclei of a particular isotope to decay.

Question 7

The mass of a radioisotope falls from 3.2g to 0.4g in 2 hours.

What is the half-life of this radioisotope?

Answer 7

3.2g→1.6g→0.8g→0.4g→0.2g
Four half-lives

4 half-lives = 2 hours
1 half-life = 0.5 hours (30 minutes)

Question 8

The half-life of a source is 8 days.

Calculate the percentage of the source that would remain after 16 days.

Answer 8

At the start, there would be 100% of the sources.

After 8 days there would be 50% (1/2) left.

After 16 days there would be 25% (1/4) left.