S2.1 The ionic model questions for IB Chemistry

123 questions on The ionic model, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.

IB Chemistry
Part of S2 Models of bonding and structure
SL and HL

Questions by paper and level

SL and HL questions are for students at either level. HL only questions cover what only HL students study.

Paper	SL and HL	HL only	All
Paper 1A	49	4	53
Paper 1B	12	2	14
Paper 2	39	17	56
Every paper	100	23	123

Counted on 10 November 2026

Questions to try

Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.

Question 1 · CHEM-00048Paper 1A · 1 mark

An atom of element X has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁴.

Which ion does X form in its ionic compounds?

A
$X^{2 -}$
B
$X^{-}$
C
$X^{2 +}$
D
$X^{6 +}$

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Question 2 · CHEM-01124Paper 1B · HL only · 9 marks

A student used data from sections 10 and 16 of the data booklet to investigate the relationship between the lattice enthalpy of the alkali metal chlorides and the sum of the ionic radii, $r_{+} + r_{-}$ .

Compound	$r_{+} + r_{-}$ / pm	$\frac{1}{r_{+} + r_{-}}$ / 10⁻³ pm⁻¹	Lattice enthalpy / kJ mol⁻¹
LiCl	257	3.891	864
NaCl	283	3.534	790
KCl	319	3.135	720
RbCl	333	3.003	695
CsCl	348	2.874	670

A spreadsheet gave a linear trend line with $R^{2} = 0.999$ .

trend line

Lattice enthalpy / kJ mol−1 against 1/(r+ + r−) / 10−3 pm−1

(a)
Explain why the lattice enthalpy increases as $\frac{1}{r_{+} + r_{-}}$ increases.
2 marks
(b)
Outline what the value of $R^{2}$ shows.
1 mark
(c)
Determine the gradient of the trend line, including its units.
2 marks
(d)
The radius of the $A g^{+}$ ion is 115 pm. Use the trend line to predict the lattice enthalpy of silver chloride.
1 mark
(e)
The experimental lattice enthalpy of AgCl in section 16 of the data booklet is 918 kJ mol⁻¹. Explain the difference from your prediction.
2 marks
(f)
State the method by which the experimental values in section 16 of the data booklet are obtained.
1 mark

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Question 3 · CHEM-00298Paper 2 · HL only · 7 marks

Limestone is mainly calcium carbonate, CaCO₃. X-ray diffraction shows that all three carbon–oxygen bonds in the carbonate ion, CO₃²⁻, have the same length.

(a)
Draw one Lewis (electron dot) formula for the carbonate ion.
1 mark
(b)
Explain why all the carbon–oxygen bonds in the carbonate ion have the same length.
2 marks
(c)
Using section 11 of the data booklet, predict the carbon–oxygen bond length in the carbonate ion.
1 mark
(d)
State the hybridization of the carbon atom and the number of σ and π bonds in the carbonate ion.
2 marks
(e)
Calculate the formal charges on the carbon atom and on a single-bonded oxygen atom in the structure you drew in (a).
1 mark

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Question 4 · CHEM-00049Paper 1A · 1 mark

Element X is in group 2 and element Y is in group 15 of the periodic table.

What is the formula of the ionic compound formed between X and Y?

A
XY
B
X₂Y₃
C
X₃Y₂
D
X₂Y

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Question 5 · CHEM-01215Paper 1B · 9 marks

A student was given four white solids, P, Q, R and S, and asked to classify their bonding and structure.

Method:

The melting point of each solid was measured (a furnace was used above 350 °C).
Two graphite electrodes, a 6 V supply and an ammeter were connected in series. The electrodes were pushed into each solid, then into the molten substance where possible.
1.0 g of each solid was stirred with 50 cm³ of deionized water and the current was measured again.

Solid	Melting point / °C ± 2 °C	Current, molten / mA	Behaviour in water	Current in water / mA
P	772	152	dissolves	98
Q	80	0.0	insoluble	0.0
R	186 (decomposes)	0.0	dissolves	0.0
S	did not melt below 1200	not measured	insoluble	0.0

(a)
Identify which solid is ionic, giving two pieces of evidence from the data.
2 marks
(b)
Solid R dissolves in water but its solution does not conduct. Outline what this shows about R.
1 mark
(c)
State two variables that should be controlled when comparing the current through the solutions in step 3.
2 marks
(d)
Suggest why the current through the solution of P is lower than through molten P.
1 mark
(e)
The student concluded that S has a covalent network structure. Evaluate this conclusion and suggest a further test.
2 marks
(f)
State one safety precaution needed when testing the conductivity of molten P.
1 mark

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Question 6 · CHEM-00428Paper 2 · 7 marks

The ionic radii of four ions are shown (section 10 of the data booklet).

Ion	S²⁻	Cl⁻	K⁺	Ca²⁺
Ionic radius / 10⁻¹² m	184	181	138	100

(a)
State the full electron configuration shared by all four ions.
1 mark
(b)
State the term used to describe species that have the same electron configuration.
1 mark
(c)
Explain why the ionic radius decreases from S²⁻ to Ca²⁺.
2 marks
(d)
Predict, giving a reason, whether the radius of the phosphide ion, P³⁻, is larger or smaller than that of S²⁻.
1 mark
(e)
Potassium chloride and calcium sulfide have the same lattice structure. Suggest, with a reason, which compound has the larger lattice enthalpy.
2 marks

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