Metals and Non-metals • Topic 2 of 3

Reactivity Series & Ionic Bonding

Different metals show different chemical reactivity. Arranging metals in decreasing order of their tendency to lose electrons gives the reactivity (activity) series. A common order is: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au. The most reactive metals are at the top; the least reactive (noble) metals are at the bottom. Hydrogen is included as a reference, even though it is not a metal.

What the series predicts

  • Reaction with water: K, Na and Ca react with cold water; Mg with hot water; metals like Fe react with steam; metals below hydrogen (Cu, Ag, Au) do not react with water at all.
  • Reaction with acids: only metals above hydrogen displace H2 from dilute acids. Copper, silver and gold (below H) do not.
  • Displacement: a more reactive metal displaces a less reactive metal from its salt solution.

Displacement reactions

If iron is placed in copper sulphate solution, the more reactive iron pushes out the less reactive copper: Fe + CuSO4 → FeSO4 + Cu. The blue colour of the solution fades and a reddish-brown copper deposit forms. The reverse (copper into FeSO4) does not happen, because copper is below iron in the series.

Why metals lose and non-metals gain electrons

Metals have 1, 2 or 3 valence electrons and tend to lose them to attain a stable noble-gas configuration, forming positive ions (cations). Non-metals have 5, 6 or 7 valence electrons and tend to gain electrons, forming negative ions (anions).

Formation of ionic (electrovalent) compounds

When a metal transfers electrons to a non-metal, oppositely charged ions form and are held together by strong electrostatic force — this is an ionic bond. In sodium chloride, sodium (2,8,1) loses one electron to become Na+ (2,8) and chlorine (2,8,7) gains it to become Cl− (2,8,8): 2Na + Cl2 → 2NaCl. In magnesium oxide, Mg loses 2 electrons and O gains 2.

Properties of ionic compounds

  • They are solids, usually hard and brittle.
  • They have high melting and boiling points because strong forces hold the ions in a lattice.
  • They are generally soluble in water but insoluble in solvents like kerosene.
  • They conduct electricity when molten or dissolved in water (ions become free to move) but not in the solid state.
Ionic bonding in NaCl: sodium transfers one electron to chlorineNa1 valence e⁻Clelectron transferNa⁺ (2,8)Cl⁻ (2,8,8)2Na + Cl₂ → 2NaCl (ionic bond)
Solved Examples
1
Worked Example
Will copper displace silver from silver nitrate solution? Write the equation.
Solution
  1. In the reactivity series copper is above silver, so copper is more reactive.
  2. A more reactive metal displaces a less reactive one from its salt solution.
  3. Equation: Cu + 2AgNO3 → Cu(NO3)2 + 2Ag; the solution turns blue and silver is deposited.

Answer: Yes; Cu + 2AgNO3 → Cu(NO3)2 + 2Ag.

2
Worked Example
Why does copper not react with dilute hydrochloric acid?
Solution
  1. Only metals placed above hydrogen in the reactivity series can displace hydrogen from acids.
  2. Copper lies below hydrogen in the series.
  3. Therefore copper cannot give electrons to H+ ions and no hydrogen gas is evolved.

Answer: Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from dilute HCl.

3
Worked Example
Describe the electron transfer in the formation of magnesium oxide (MgO).
Solution
  1. Magnesium has the configuration 2,8,2 and loses its 2 valence electrons to become Mg2+ (2,8).
  2. Oxygen has the configuration 2,6 and gains those 2 electrons to become O2− (2,8).
  3. The oppositely charged ions Mg2+ and O2− attract strongly: 2Mg + O2 → 2MgO.

Answer: Mg loses 2 electrons to form Mg2+ and O gains them to form O2−, giving ionic MgO.

4
Worked Example
Why do ionic compounds conduct electricity when molten or in solution but not in the solid state?
Solution
  1. In the solid state the ions are locked in fixed positions in the crystal lattice and cannot move.
  2. On melting or dissolving in water, the lattice breaks and the ions become free to move.
  3. These free, mobile ions carry the electric current.

Answer: Conduction needs free-moving ions, which exist only in the molten or aqueous state, not in the rigid solid.

5
Worked Example
Why do ionic compounds have high melting and boiling points?
Solution
  1. Ionic compounds consist of positive and negative ions arranged in a regular lattice.
  2. The electrostatic force of attraction between the oppositely charged ions is very strong.
  3. A large amount of heat energy is needed to overcome this force, so the melting and boiling points are high.

Answer: Strong electrostatic attraction between ions in the lattice requires much energy to break, giving high melting and boiling points.

6
Worked Example
Arrange Zn, Mg, Cu and Fe in decreasing order of reactivity.
Solution
  1. Recall the reactivity series order: Mg > Zn > Fe > Cu.
  2. Magnesium is the most reactive of the four; copper is the least.
  3. So the decreasing order is Mg, then Zn, then Fe, then Cu.

Answer: Mg > Zn > Fe > Cu.

Key Points

  • The reactivity series ranks metals by their tendency to lose electrons: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
  • Only metals above hydrogen displace H2 from dilute acids; a more reactive metal displaces a less reactive one from its salt (Fe + CuSO4 -> FeSO4 + Cu).
  • Metals lose electrons to form cations; non-metals gain electrons to form anions, both attaining noble-gas configurations.
  • An ionic (electrovalent) bond forms by transfer of electrons from a metal to a non-metal, e.g. 2Na + Cl2 -> 2NaCl.
  • Ionic compounds are hard solids with high melting points, soluble in water, and conduct electricity only when molten or dissolved.
Quick Check — 4 MCQs
Tap an option to check your answer0 / 4
Q1.Which metal is the most reactive in the list below?
Explanation: Potassium is near the top of the reactivity series, far above iron, zinc and copper.
Q2.In the reaction Fe + CuSO4 → FeSO4 + Cu, iron displaces copper because:
Explanation: A more reactive metal (iron) displaces a less reactive metal (copper) from its salt solution.
Q3.An ionic bond is formed by:
Explanation: Ionic bonds form when a metal transfers electrons to a non-metal, producing oppositely charged ions.
Q4.Ionic compounds conduct electricity when:
Explanation: Free-moving ions exist only in the molten or aqueous state, so conduction occurs only then.
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