1.1. The atomic model developed by scientists has changed over time as experimental evidence improved understanding.

Explain how Niels Bohr contributed to the atomic model. 

1.2. Compare the relative atomic masses and relative atomic charges of the subatomic particles within an atom. 

1.3. Higher Tier Only

Figure 1 shows the percentage abundance of two isotopes of chlorine.

Figure 1

Calculate the relative atomic mass of chlorine. 

1.4. Explain why carbon-12 and carbon-13 are isotopes of the same element.

Give your answer in terms of subatomic particles.