2 This question is about atomic structure and the periodic table.
Gallium (Ga) is an element that has two isotopes.
2-1 Give the meaning of ‘isotopes’.
You should answer in terms of subatomic particles. [2 marks]
ANSWER
Atoms with the same number of protons but different numbers of neutrons are called isotopes.
2-2 Table 1 shows the mass numbers and percentage abundances of the isotopes of gallium
Table 1
Calculate the relative atomic mass (Ar) of gallium.
Give your answer to 1 decimal place. [2 marks]
ANSWER
2-3 Gallium is in group 3 of Periodic table
Give the numbers of electrons and neutrons in an atom of the isotope 69Ga31
Number of electrons _________________
Number of neutrons _________________
ANSWER
Number of electrons 31
Number of neutrons (69-31)=38
2-4 What is the most likely formula of a gallium ion? [1 mark]
ANSWER
Ga3+
2-5 Gallium was discovered six years after Mendeleev published his periodic table.
Give two reasons why the discovery of gallium helped Mendeleev’s periodic table to become accepted. [2 marks]
ANSWER
Gallium fitted in a gap which Mendeleev had left, i.e. gallium’s properties were predicted correctly by Mendeleev.
