37 exam-style questions on The nuclear atom — topic S1.2 of Structure 1: Models of the particulate nature of matter in the IB Chemistry syllabus — with answers and explanations. Samples below; the full set is free with an account.
What is the full ground-state electron configuration of an iron atom (Z = 26)?
Answer: 1s²2s²2p⁶3s²3p⁶4s²3d⁶
The 4s sub-shell fills before 3d, giving [Ar]4s²3d⁶ for the 26 electrons of iron.
State the relative charge and relative mass of a neutron.
Answer: Charge 0, mass 1
A neutron has no charge and a relative mass of 1; the electron has the very small relative mass of about 1/1840.
An atom is represented as ³⁷₁₇Cl. Determine the number of neutrons it contains.
Answer: 20
Neutrons = mass number - atomic number = 37 - 17 = 20; protons equal the atomic number 17.
In a sample entering a mass spectrometer, state which process gives the particles a positive charge so they can be deflected.
Answer: Ionisation
Ionisation (usually electron bombardment) removes electrons to form positive ions; these are then accelerated, deflected by their m/z, and detected.
Neon consists of 90.5 % ²⁰Ne and 9.5 % ²²Ne. A student states that the relative atomic mass of neon is 21.0, the mean of the two isotopic masses. Deduce what is wrong with this value.
Answer: It is too high, because the lighter isotope is far more abundant than the heavier one.
Relative atomic mass is the abundance-weighted mean, so with 90.5 % of the atoms at mass 20.0 the value must sit close to 20.2 rather than midway at 21.0. Electrons are far too light to affect it, and abundance is a count of atoms — a heavier isotope is not weighted more heavily than its share.
A particle contains 16 protons, 16 neutrons and 18 electrons. Deduce its symbol.
Answer: ³²S²⁻
The proton number identifies the element (16 = sulfur) and the mass number counts protons plus neutrons only, 16 + 16 = 32; electrons have negligible mass and never enter the mass number, which rules out 34. Two electrons more than protons gives a 2− charge, not 2+, and the element must never be read off the electron count, which is what gives argon.
That was 6 of 37 The nuclear atom questions.
Practise all 37 freeStateAO1 · 1–2 marks
One word or one short sentence. No explanation, no working: the mark is for the fact itself.
DefineAO1 · 1–2 marks
Give the precise meaning — one sentence, the key terms in it, no example needed unless asked.
DrawAO1 · 1–2 marks
A labelled, accurate drawing with a ruler where lines are straight; axes and units on a graph.
All of Structure 1: Models of the particulate nature of matter →
37 The nuclear atom questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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