Ionic bonding holds ions together in a giant lattice. Covalent bonds create simple molecules or giant covalent structures. Different types of bonding give a substance different properties – different melting and boiling points, different electrical conductivity, and different solubility in water, among much else.
Metals are giant lattices of positive ions arranged in regular layers, with delocalised electrons free to move throughout the structure. Their properties include:
high melting and boiling points. High temperatures are required to break strong metallic bonds.
good electrical conductivity. Metal’s delocalised electrons can move and carry charge.
malleable and ductile. Metal’s layers of ions can slide over each other, but are still held together by the delocalised electrons. This means metal is malleable (it can be hammered into shape) and ductile(it can be drawn out into wires).
An alloy is a mixture of two or more elements, at least one of which is a metal. The mixture has metallic properties.