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1.4.2Physical Chemistry

Ionic Bonding — AQA AS Chemistry Revision Notes & Topical Questions

5 min read 4 parts Lesson 18 of 102

📚 AQA AS Chemistry Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 4Forming Ions

Electron transfer
  • Electron transfer Ionic bonding occurs between a metal and a non-metal when the metal atom gives up electrons and the non-metal atom accepts them.
Cations
  • Cations Metals lose their outer electrons to form positive ions, for example Na → Na⁺ + e⁻, leaving a full outer shell beneath.
Anions
  • Anions Non-metals gain electrons to form negative ions, for example Cl + e⁻ → Cl⁻, which gives them a full outer shell.
Ionic bond
  • Ionic bond The ionic bond is the strong electrostatic attraction between the oppositely charged ions, acting equally in all directions.
Ion charges
  • Ion charges Group 1, 2 and 3 metals form 1+, 2+ and 3+ ions, while Group 15, 16 and 17 non-metals form 3−, 2− and 1− ions respectively.

Part 2 of 4Giant Ionic Lattice

Giant Ionic Lattice
Regular array
  • Regular array Ions are packed in a repeating three-dimensional pattern in which each ion is surrounded by oppositely charged neighbours.
Sodium chloride
  • Sodium chloride In NaCl each Na⁺ is surrounded by six Cl⁻ ions and each Cl⁻ by six Na⁺, giving a cubic arrangement.
Formula
  • Formula The formula shows the simplest ratio of ions needed for overall neutrality, so magnesium chloride is MgCl₂ and aluminium oxide is Al₂O₃.
Strength
  • Strength Attraction increases with higher ionic charge and smaller ionic radius, so MgO has a stronger lattice than NaCl.

Part 3 of 4Writing Ionic Formulae

1
Identify the metal and non-metal and decide the charge on each ion from its group in the periodic table.
2
Balance the charges by finding the smallest numbers of each ion so that total positive charge equals total negative charge.
3
Write the formula with the cation first and subscripts for the numbers of ions, omitting any subscript of 1.
4
For compound ions such as sulfate SO₄²⁻ or nitrate NO₃⁻ use brackets when more than one is needed, as in Ca(NO₃)₂.
5
Check that the overall charge is zero, because ionic compounds are electrically neutral.
CompoundIonsFormula
Sodium oxideNa⁺, O²⁻Na₂O
Calcium chlorideCa²⁺, Cl⁻CaCl₂
Aluminium oxideAl³⁺, O²⁻Al₂O₃

Part 4 of 4Exam Checklist & Tips

1.4.2 – Key Points for the Exam

  • Ion An atom or group of atoms with an overall positive or negative charge.
  • Ionic bond The electrostatic attraction between oppositely charged ions.
  • Giant ionic lattice A regular three-dimensional arrangement of oppositely charged ions held by ionic bonds.
  • Isoelectronic Having the same electron configuration, such as Na⁺ and Mg²⁺ both with 2,8.

Common Mistakes

  • Describing an ionic bond as a shared pair of electrons; that is covalent bonding.
  • Saying that a molecule of NaCl exists; an ionic compound is a giant lattice, not a molecule.
  • Writing the charge as 2 on a magnesium ion instead of 2+, or forgetting charges on dot and cross diagrams.
  • Claiming that only one ion attracts another; each ion attracts all oppositely charged ions around it.

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