The elements in the third period exhibit periodicity in both their chemical and physical properties.

1. (a)(i)A graph of the atomic and ionic radii across the third period is shown. [Figure: Bar chart showing atomic and ionic radii for Na, Na⁺, Mg, Mg²⁺, Al, Al³⁺, Si, Si⁴⁺, P, P³⁻, S, S²⁻, Cl, Cl⁻] Explain the decrease in atomic radius across the third period.[2]
2. (a)(ii)Explain why, for sodium to silicon, the ionic radii are less than the atomic radii.[1]
3. (a)(iii)Explain why, for phosphorus to chlorine, the ionic radii are greater than the atomic radii.[2]
4. (b)(i)The first ionisation energies of the elements across the third period show a general increase. Aluminium and sulfur do not follow this general trend. Explain why aluminium has a lower first ionisation energy than magnesium.[2]
5. (b)(ii)Explain why sulfur has a lower first ionisation energy than phosphorus.[2]
6. (c)(i)The elements in the third period, from sodium to silicon, can react with chlorine to form chlorides. State and explain the pattern of change of oxidation number which occurs to both chlorine and the different Period 3 elements when they react together.[3]
7. (c)(ii)Give the equations to show the reactions of sodium chloride and silicon(IV) chloride when separately added to water. sodium chloride silicon(IV) chloride[2]
8. (c)(iii)Complete the table to describe the structure and bonding in sodium chloride and silicon(IV) chloride. structure | bonding --- | --- sodium chloride | silicon(IV) chloride | [2]

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