Test Yourself 2.4 (Textbook) – Chemistry Form 4 Chapter 2 (Matter and the Atomic Structure)

Question 1:
Define isotopes.

Answer:
Isotopes are atoms of the same element with the same proton number / same number of protons but with different nucleon number / number of neutrons.

Question 2:

Based on Table 2.6, which atoms are isotopes?
Explain your answer.

Answer:
Atoms W and X
This is because the atom W and X have the same number of protons / same number of protons but different nucleon number / number of neutrons.

Question 3:
 Atoms of oxygen-16, oxygen-17 and oxygen-18 are isotopes. Compare and contrast these three isotopes.

Answer:
Similarity:
• This atom is from the same element, that is oxygen

• The number of protons in the nucleus of this atom is the same

• The chemical properties of these atoms are the same

Differences:
• The nucleon number of all three atoms is different. The nucleon number for oxygen-16 is 16, the nucleon number for oxygen-17 is 17 and the nucleon number for oxygen-18 is 18.

• The number of neutrons in the nucleus of all three atoms is different. Oxygen-16 has 8 neutrons, oxygen-17 has 9 neutrons and oxygen-18 has 10 neutrons.

• The physical properties of all three atoms are different.

Question 4:
 Magnesium exists naturally as three isotopes, which are 79.0% of ²⁴Mg, 10.0% of ²⁵Mg and 11.0% of ²⁶Mg.
Calculate the relative atomic mass of magnesium.

Answer:
$$\text { Relative atomic mass of magnesium }$$
$$\begin{aligned} & =\frac{(79.0 \times 24)+(10.0 \times 25)+(11.0 \times 26)}{100} \\ & =24.32 \end{aligned}$$

Question 5:
Madam Maimunah was diagnosed with bone cancer.
(a) What isotope is used to treat Madam Maimunah?
(b) Explain the positive and negative effects of using the isotope in (a).

Answer:
(a) Cobalt-60

(b)
Positive effect:
• Cancer cells can be killed

Negative effect:
• Immunity system is weakened
• Hair loss