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1.4.1Physical Chemistry

Ionic Bonding Overview — Edexcel AS Chemistry Revision Notes & Topical Questions

5 min read 4 parts Lesson 10 of 42

📚 Edexcel AS Chemistry Hub / Topical Revision
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Part 1 of 4Electron Transfer

1.4.1 Ionic Bonding Overview

Ionic compounds form most easily between elements on the left and right of the Periodic Table.

Definition
  • Ionic bonding is the electrostatic attraction between oppositely charged ions in a lattice.
Metals
  • Metals lose their outer electrons to become positive ions (cations), often reaching a noble gas configuration.
Non-metals
  • Non-metals gain electrons to become negative ions (anions), also reaching a full outer shell.
Electrostatic force
  • The attraction acts equally in all directions, so each ion attracts many neighbours rather than only one partner.
Noble gas structure
  • The ions formed usually have the electron arrangement of the nearest noble gas,
    • such as Na⁺ and Cl⁻ matching neon and argon respectively.

Part 2 of 4Predicting Charges

Predicting Charges
Group 1
  • Atoms lose one electron to form 1+ ions, such as Na⁺ and K⁺.
Group 2
  • Atoms lose two electrons to form 2+ ions, such as Mg²⁺ and Ca²⁺.
Group 16
  • Atoms gain two electrons to form 2- ions, such as O²⁻ and S²⁻.
Group 17
  • Atoms gain one electron to form 1- ions, such as Cl⁻ and Br⁻.
Transition metals
  • Many transition metals form ions with more than one charge,
    • such as Fe²⁺ and Fe³⁺,
    • so their charges are not predicted from the group number.
CompoundIonsFormula check
Sodium chlorideNa⁺ and Cl⁻1 + 1 = neutral
Magnesium oxideMg²⁺ and O²⁻2 + 2 = neutral
Calcium chlorideCa²⁺ and 2 Cl⁻2 = 2 × 1

Part 3 of 4The Giant Lattice

1
Many ions arrange themselves in a regular repeating three-dimensional pattern called a giant ionic lattice.
2
In sodium chloride each Na⁺ is surrounded by six Cl⁻ ions and each Cl⁻ by six Na⁺ ions.
3
Opposite charges attract strongly, while like charges are held apart, so the structure is stable.
4
The empirical formula gives the simplest ratio of ions needed to balance the total charge.
5
Because there are no separate molecules, the formula is a ratio and not a count of atoms in a molecule.

Part 4 of 4Exam Checklist & Tips

1.4.1 – Key Points for the Exam

  • Ionic bond The electrostatic attraction between oppositely charged ions.
  • Cation A positive ion formed when an atom loses electrons.
  • Anion A negative ion formed when an atom gains electrons.
  • Giant ionic lattice A regular three-dimensional arrangement of alternating positive and negative ions.

Common Mistakes

  • Describing an ionic bond as a shared pair of electrons.
  • Saying one sodium ion is bonded only to one chloride ion; each ion attracts all its neighbours.
  • Writing a formula for ionic compounds as a molecule instead of the simplest ratio.
  • Believing that atoms gain or lose electrons to be happy rather than to reach a lower-energy, stable arrangement.

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