How do I start a bonding question?

Decide whether each partner is a metal or a non-metal, then whether electrons transfer or are shared.

How do melting point and conduction link?

Melting depends on the forces to overcome, conduction on whether ions or electrons can move.

S4 Chemistry: Chemical Bonding and Structure (Paper 2)

2026-11-01

The second paper practises electron transfer diagrams, ion ratios and formula masses, working back from formulae to charges.

Direct answer　Count the outer electrons first, then decide transfer or sharing; check a formula by making the total charge zero before finding the formula mass.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S4 Chemistry: Chemical Bonding and Structure
Level	Four basic, three advanced, two challenge and one error-repair item

02　Questions (10 items)

FoundationFor sodium chloride, give the electron arrangements of the two ions.
FoundationGive the ratio of magnesium ions to oxide ions in magnesium oxide and explain it.
FoundationGive the ion ratio in calcium fluoride CaF2.
FoundationFind the relative molecular mass of water with H = 1 and O = 16.
IntermediateFind the relative molecular masses of CO2 and CH4 with C = 12, O = 16 and H = 1.
IntermediateFind the relative formula mass of MgCl2 with Mg = 24 and Cl = 35.5.
IntermediateHow many bonding pairs and lone pairs are there in an ammonia molecule?
ChallengeA compound has the formula XCl2. Give the charge on X and say whether a Group 2 metal fits.
ChallengeWhy is the radius of Na+ smaller than that of the sodium atom?
Error redoError repair: a student draws the Na+ ion with eleven electrons arranged 2,8,1. Correct it.

03　Answers and one-line notes

#	Answer	One-line note
1	Na+ 2,8 and Cl- 2,8,8	Sodium loses its single outer electron to give 2,8 while chlorine gains one to give 2,8,8.
2	one to one	A plus two and a minus two charge cancel one to one, so the formula is MgO.
3	one calcium to two fluoride	One calcium ion needs two fluoride ions, since plus two plus two times minus one is zero.
4	18	Two times one plus sixteen gives eighteen.
5	CO2 44, CH4 16	Carbon dioxide is 12 plus 32 and methane is 12 plus 4.
6	95	Twenty four plus seventy one gives ninety five, and ionic compounds use formula mass rather than molecular mass.
7	three bonding pairs and one lone pair	Nitrogen shares one pair with each hydrogen and keeps one lone pair, giving eight outer electrons in all.
8	plus 2, and Group 2 fits	Two chloride ions give minus two in total, so X must be plus two, matching a Group 2 metal that loses two electrons.
9	the outer shell is lost, leaving 2,8	The sodium atom is 2,8,1 but the ion is 2,8, so the whole third shell is gone and the radius shrinks.
10	Na+ has ten electrons arranged 2,8	The outer electron is lost when the ion forms, so drawing 2,8,1 still shows an atom rather than an ion.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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