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4CH1

Ionic Bonding

Principles of Chemistry · 2 question types

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4CH1 Topics

States of Matter6%
Elements, Compounds and Mixtures5%
Atomic Structure9%
The Periodic Table8%
Chemical Formulae, Equations and Calculations17%
Ionic Bonding9%
  1. Formation of Ions
  2. Common Ions
  3. Formula of an Ionic Compound
  4. Dot-and-cross Diagrams for Ionic Bonds
  5. Structure and Properties of Ionic Compounds
Covalent Bonding8%
Metallic Bonding5%
Electrolysis7%

Frequency legend

High (≥14%)
Above avg (10 to 13%)
Average (<10%)

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 9% of your exam marks.

stable
Medium
Stable9%

Ion formation, lattice structures and properties of ionic compounds tested consistently.

What an ion is

  • An ion is a charged atom (or group of atoms) formed when an atom loses or gains electrons
  • The number of electrons transferred equals the size of the charge:
    • lose 1 electron → 1+ charge
    • lose 2 electrons → 2+ charge
    • gain 1 electron → 1− charge
    • gain 2 electrons → 2− charge

Cations and anions

  • A cation is a positive ion, formed when an atom loses electrons (it now has fewer electrons than protons)
  • An anion is a negative ion, formed when an atom gains electrons (it now has more electrons than protons)
  • The driving force in every case is to reach a full outer shell — the stable electron arrangement of a noble gas
    • Metals (1–3 outer electrons) lose those few electrons to form cations
    • Non-metals (5–7 outer electrons) gain electrons to form anions
  • Group 4 elements rarely form simple ions (losing or gaining 4 electrons costs too much energy)
  • Group 0 noble gases already have full outer shells and so do not form ions

Predicting ion charges from group number

GroupOuter electronsIon charge
111+
222+
333+
553−
662−
771−
Exam tip

Describing electron changes when ions form

What comes up: "Describe the changes in electronic configuration of [metal] and [non-metal] atoms to form the ions in [compound]."

Write (two marks): (1) State that the metal atom loses the correct number of electrons (e.g. each sodium atom loses one electron, changing from 2,8,1 to 2,8). (2) State that the non-metal atom gains the correct number of electrons (e.g. the oxygen atom gains two electrons, changing from 2,6 to 2,8).

Watch out: Any mention of sharing electrons scores zero for this type of question — describe electron transfer (loss and gain), never sharing. Name each atom separately and state the specific number of electrons it loses or gains.