1hMetallic bonding

Separate Chemistry only.

A metal is not made of atoms sitting next to each other. Every metal atom gives up its outer-shell electrons, and what remains is a regular lattice of positive metal ions with those electrons flowing freely between them.

The structure

• Positive metal ions, arranged in a regular repeating pattern.
• Delocalised electrons in the spaces between them, free to move throughout the whole structure.

Delocalised means the electrons no longer belong to any particular atom. They came from the outer shells, and now they belong to the metal as a whole.

What the bond is

Metallic bonding is the strong electrostatic attraction between the positive metal ions and the delocalised electrons.

Two mistakes to avoid in that sentence:

• The lattice contains only positive ions. Describing positive and negative ions is ionic bonding, not metallic.
• The attraction is between the ions and the electrons, not between one ion and another. Two positive ions would repel; it is the electron sea between them that holds everything together.

Why the strength varies between metals

Magnesium melts at a much higher temperature than sodium. The reason is what each atom contributes.

A sodium atom releases one electron and becomes Na⁺. A magnesium atom releases two and becomes Mg²⁺.

So magnesium has ions of higher charge and more delocalised electrons, which makes the attraction stronger and the melting point higher.

When comparing two metals, compare the ion charge first — as with ionic compounds, it is usually the answer.

Separate Chemistry only.

The two properties metals are used for both come from the same structure.

Electrical conductivity

Metals conduct because their delocalised electrons are free to move. Apply a voltage and the electrons drift through the metal, and a flow of charge is a current.

Note what moves: the electrons, not the ions. The positive ions stay in their lattice positions throughout.

This is why a metal conducts as a solid, where an ionic compound cannot. An ionic solid has charged particles but they are locked in place; a metal has charged particles that were mobile from the start.

Thermal conductivity

The same free electrons carry energy. They pick it up at the hot end, move, and transfer it as they collide — which is far faster than passing vibrations from atom to atom.

That is why a metal spoon in hot tea heats up quickly and a plastic one does not.

Malleability

Metals can be hammered into shape without shattering. Two things make that possible:

1. The ions sit in layers that can slide over one another when a force is applied.
2. After sliding, the delocalised electrons still hold the structure together, because they are spread through the whole metal rather than tied to particular positions.

That second half is what a full answer needs. Sliding alone would explain something falling apart; it is the bonding surviving the slide that explains a metal bending rather than breaking.

Compare with an ionic solid

An ionic lattice shatters when struck. Sliding its layers brings like charges next to each other, and they repel.

A metal has no such problem — the ions are all positive and the electron sea flows around them wherever they end up.