The metallic bond: ions in a sea of electrons

Why metals behave like metals

Your book lists five properties of metals: lustre, usually high melting and boiling points, good conduction of heat and electricity, usually hard and heavy, and shapes that change under pressure.

Metal atoms hold their outer electrons loosely. In sodium metal each atom has eight neighbours, and the outer electrons move freely through the spaces between atoms.

No electron belongs to one nucleus; all the nuclei attract all the electrons. The metal is like positive ions sitting in a sea of electrons. That pull is the metallic bond.

Its strength depends on the charge on the ions and the number of electrons each atom sets free. Sodium frees one, magnesium two, so magnesium's bond is stronger and it melts higher.

Free electrons carry heat and electricity; rows of atoms that slip let metals become wires and sheets.

Key terms

Metallic bond

Holding the atoms of a metal together.

Sea of electrons

Picturing the free outer electrons of a metal.

Malleable

Rows of atoms slip but stay bonded.

Ductile

Making electric wires.

Short questions with model answers

1. Q1. Why does magnesium melt at a higher temperature than sodium? (p. 42)

   • Na → Na⁺ + 1 free electron
   • Mg → Mg²⁺ + 2 free electrons
   • More charge, more electrons → stronger bond

   Magnesium's metallic bond is stronger (2+ ions, two electrons each), so it melts higher.

2. Q2. Why can metals be drawn into wires? (Fig 3.11, p. 43)

   • Atoms sit in rows
   • Pressure → rows slip
   • The electron sea still holds them

   The rows slip without the bond breaking, so the shape changes: wires and sheets.

Common mistakes

• ✗ Metal atoms share fixed electron pairs, like a covalent bond.

  ✓ No electron stays with any one nucleus; the electrons move freely among all the ions.

• ✗ A metal is an ionic compound because it contains positive ions.

  ✓ There are no negative ions; the positive ions are held by mobile electrons.

• ✗ All metallic bonds are equally strong.

  ✓ More charge and more free electrons per atom give a stronger bond: Mg is stronger than Na.

MCQs

1. 1. Molten copper and molten zinc mix to give brass. What bond forms between copper and zinc?

   1. (a) Coordinate covalent
   2. (b) Ionic
   3. (c) Metallic
   4. (d) Covalent
   Show answer

   (c) Exercise MCQ (i), p. 49: both are metals, so their ions share one sea of electrons.

2. 2. Why are metals good conductors of electricity?

   1. (a) They contain freely moving electrons
   2. (b) Their atoms are heavy
   3. (c) They have lustre
   4. (d) They contain negative ions
   Show answer

   (a) p. 42: freely moving electrons make metals good conductors of heat and electricity.

3. 3. The strength of a metallic bond depends on:

   1. (a) The colour of the metal
   2. (b) The size of the sample
   3. (c) The number of neutrons
   4. (d) The ion charge and the number of free electrons
   Show answer

   (d) p. 42: two factors, the positive charge on the ions and the number of mobile electrons per atom.

4. 4. Which property of metals makes them malleable and ductile?

   1. (a) Their lustre
   2. (b) Rows of atoms that slip under pressure
   3. (c) Their high density
   4. (d) Their negative ions
   Show answer

   (b) Short Q iv, p. 51; p. 42: the upper rows slip past the lower rows, so the shape changes.

5. 5. How many electrons does each magnesium atom release into the electron sea?

   1. (a) 1
   2. (b) 3
   3. (c) 4
   4. (d) 2
   Show answer

   (d) p. 42: each magnesium atom releases two electrons and becomes 2+.

Quick revision

• A metallic bond is positive ions held together by a sea of mobile electrons.
• More charge and more free electrons per atom give a stronger bond (Mg over Na).
• Free electrons explain conduction; slipping rows explain wires and sheets.