Tutoring hours from just $25! N26 IB exam session special: Biology, Chemistry and Economics $25, Maths SL and English $35, until 12 November.
LimeAdmissionsPractice

Practice · Chemistry · 2025 syllabus · S2.1

IB Chemistry S2.1 The ionic model: practice questions

6 exam-style questions on S2.1 The ionic model, SL and HL: 4 multiple choice and 2 structured. Each one comes with the mark scheme, a model answer and the reasoning behind every mark. Free with your email.

Try one

S2.1-01 · Paper 1A style · multiple choice · 1 mark

Ions in magnesium phosphide

Which row shows the formula of magnesium phosphide and the electron configurations of the ions in it? [1]

  1. Mg2P3; Mg ion [Ne]; P ion [Ar]
  2. Mg3P2; Mg ion [Ne] 3s2; P ion [Ne] 3s2 3p3
  3. Mg3P2; Mg ion [Ne]; P ion [Ar]
  4. Mg2P3; Mg ion [Ne] 3s2; P ion [Ne] 3s2 3p3
Show the answer and the reasoning

Answer: C. C is correct. Magnesium loses two electrons (Mg2+, [Ne]) and phosphorus gains three (P3−, [Ar]). Charges balance with 3 Mg2+ and 2 P3−: Mg3P2. A swaps the subscripts. B gives the configurations of the neutral atoms, the error most candidates made on this item type in May 2025. D combines both mistakes.

The other 5 open with your email, with the same mark scheme and reasoning.

Open the questions

Free while in beta. Type your email and every question opens straight away.

Signed up before, here or for our past-paper links? Use the same email and you are straight in, on any device. You also get our occasional email on IB exam technique and what we offer. Unsubscribe in any message. How the address is handled.

You are in. Every S2.1 question is open, with your progress.

Open the S2.1 questions

The 6 questions in S2.1

  1. S2.1-01 Ions in magnesium phosphidePaper 1A style · multiple choice · 1 mark
  2. S2.1-02 Formula with a polyatomic ionPaper 1A style · multiple choice · 1 mark
  3. S2.1-03 Properties of an ionic solidPaper 1A style · multiple choice · 1 mark
  4. S2.1-04 Largest lattice enthalpyPaper 1A style · multiple choice · 1 mark
  5. S2.1-05 How calcium chloride formsPaper 2 style · structured question · 6 marks
  6. S2.1-06 Comparing lattice enthalpiesPaper 2 style · structured question · 5 marks

More of S2 Models of bonding and structure

Every Chemistry topic · Biology, Chemistry and Economics

Stuck on a topic?

Go through it with a tutor, the first 30 minutes free.

Biology, Chemistry and Economics, one to one, online.

Book the free session

Free live sessions

Join 100+ IB students in our free live sessions.

Exam technique for IB Biology, Chemistry and Economics, live on Zoom. Follow the calendar and every new session reaches you.

See the free sessions →

Every Biology and Chemistry question here is original, written for practice in the style of the papers set since the 2025 syllabus, with invented data. Developed independently from the International Baccalaureate Organization, which has not endorsed it. Found a mistake? Email vytis@limeadmissions.com with the question id.