The bar chart shows the melting points of the elements in Period 3 of the periodic table.
(a) Use the bar chart to give the melting point of silicon (Si). [1]
(b) Name the three elements in Period 3 that are metals. [1]
(c) A student says:
“All elements with a melting point above 500 °C are metals, and all elements with a melting point below 500 °C are non-metals.”
Evaluate the student’s statement. Use the bar chart and your answer to part (b). [3]
- (a) any value from 1400 to 1430 (°C)(1)
- (b) sodium, magnesium and aluminium all three needed; allow Na, Mg, Al(1)
- (c) magnesium and aluminium (are metals and) have melting points above 500 °C, so these support the statement allow either one named(1)
- (c) but silicon has a melting point above 500 °C / of about 1400 °C and is a non-metal allow silicon is not a metal or but sodium has a melting point below 500 °C / of about 100 °C and is a metal(1)
- (c) so the statement is not correct / melting point alone cannot be used to classify an element as a metal or non-metal allow conclusion only if at least one counter-example (Si or Na) is given; allow suggestion of a better test e.g. electrical conductivity or type of ion formed(1)
- Answer: (a) about 1414 °C (b) Na, Mg, Al (c) Mg and Al fit, but Si (high mp, non-metal) and Na (low mp, metal) do not, so the statement is wrong
- Examiner tip: ‘Evaluate’ needs evidence on both sides and a conclusion – quote the data for at least one element that breaks the rule.