S1.3 Electron configurations questions for IB Chemistry

146 questions on Electron configurations, 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 S1 Models of the particulate nature of matter
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	44	28	72
Paper 1B	8	7	15
Paper 2	32	27	59
Every paper	84	62	146

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-00997Paper 1B · HL only · 8 marks

A student used a database to investigate the strength of metallic bonding across period 4, using the enthalpy of atomization, ΔH_at (the enthalpy change to form one mole of gaseous atoms from the element in its standard state).

Element	K	Ca	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn
Number of 3d + 4s electrons	1	2	3	4	5	6	7	8	9	10	11	12
ΔH_at / kJ mol⁻¹	89	178	378	470	514	397	281	416	425	430	338	131

The student drew a straight line through the points for K and Ca and extended it.

line through K and Ca

ΔHat / kJ mol⁻¹ against number of 3d + 4s electrons

(a)
Suggest why the enthalpy of atomization is a better measure of the strength of metallic bonding than the melting point.
1 mark
(b)
Use the line to predict ΔH_at for scandium and calculate the percentage error of this prediction, taking the database value as correct.
2 marks
(c)
Suggest why scandium's actual value is higher than the line predicts, although the line already allows for its extra delocalized electron.
2 marks
(d)
From chromium onwards, the values lie well below the line. Suggest a reason, with reference to the electron configurations.
2 marks
(e)
Identify the element in the series Ti to Ni that does not follow the general pattern of its neighbours.
1 mark

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Question 3 · CHEM-00425Paper 2 · 8 marks

Selenium, Se, is used in photocells and is an essential trace element in the human diet. Use section 7 of the data booklet.

(a)
State the period and the group number of selenium.
1 mark
(b)
Identify the block of the periodic table in which selenium is found.
1 mark
(c)
Deduce the full electron configuration of a selenium atom.
1 mark
(d)
State the number of valence electrons in a selenium atom.
1 mark
(e)
Deduce the formula of the ion that selenium forms in ionic compounds and the formula of sodium selenide.
2 marks
(f)
The electronegativity of selenium is lower than that of sulfur. Explain this difference.
2 marks

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Question 4 · CHEM-00052Paper 1A · 1 mark

Which ion has the same electron configuration as an argon atom?

A
$A l^{3 +}$
B
$F^{-}$
C
$N a^{+}$
D
$S^{2 -}$

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Question 5 · CHEM-01027Paper 1B · 9 marks

A student used a hand-held spectroscope with a wavelength scale to identify the metal ions in three unknown salts, A, B and C. A nichrome wire loop was dipped in each salt and held in a non-luminous Bunsen flame.

Before testing, the student checked the spectroscope with a sodium lamp, which emits light of wavelength 589 nm. The scale read 593 nm.

Table 1: literature wavelengths of the main emission lines

Metal	Main lines / nm
barium	554
copper	511, 522
lithium	610, 671
potassium	404, 767
sodium	589
strontium	461, 641

Table 2: the student's results

Sample	Flame colour	Scale readings of lines / nm ± 2 nm
A	crimson red	614, 675
B	lilac	408 (faint), 771
C	pale green	558

(a)
Identify the type of error shown by the reading for the sodium lamp, giving a reason.
1 mark
(b)
Correct the readings for sample A and hence identify the metal ion it contains.
2 marks
(c)
Identify the metal ions in samples B and C.
1 mark
(d)
All three samples also gave a weak line at a scale reading of 593 nm. Suggest an explanation.
1 mark
(e)
Suggest one modification to the method that would reduce the problem identified in (d).
1 mark
(f)
Explain why each metal gives its own characteristic set of lines.
2 marks
(g)
Outline one limitation of identifying the metal ions from the flame colour by eye alone.
1 mark

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Question 6 · CHEM-00426Paper 2 · 8 marks

In 1871 Mendeleev left a gap in his periodic table below silicon and predicted the properties of the missing element, which he called eka-silicon. The element, germanium, Ge, was discovered in 1886.

(a)
State the period and block in which germanium is found.
1 mark
(b)
Deduce the condensed electron configuration of germanium.
1 mark
(c)
Germanium is classified as a metalloid. State one property that is typical of a metalloid.
1 mark
(d)
Predict the formulas of the oxide and the chloride of germanium in which germanium has the same oxidation state as silicon in $S i O_{2}$ .
2 marks
(e)
The first ionization energy of germanium is 762 kJ mol⁻¹ and that of carbon is 1086 kJ mol⁻¹. Explain this difference.
2 marks
(f)
Suggest why Mendeleev left gaps rather than placing the next known element directly below silicon.
1 mark

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