Metallic Bonding

When metal atoms come together, each atom contributes its outer electron(s) to a shared 'sea' that flows around the structure. The atoms become POSITIVE IONS (because they've lost outer electrons) sitting in a regular lattice. The delocalised electrons are everywhere at once.

The strong electrostatic attraction between the lattice of positive ions and the negative electron sea is the metallic bond. It extends throughout the entire piece of metal.

Good electrical conductor. Free electrons can drift through the metal — that's an electric current. Works in solid metal too (unlike ionic compounds, which need to be molten).

Good thermal conductor. Free electrons carry kinetic energy too. They speed up at the hot end and transfer energy down the metal by collisions.

Malleable and ductile. Push hard enough and ion layers slide over each other. The electron sea adjusts smoothly — the metallic bond isn't broken, just rearranged. So metal can be hammered into sheets (malleable) or pulled into wires (ductile).

High melting and boiling points. Strong attraction between ions and electron sea needs lots of energy to overcome. Mercury is a rare exception — liquid at room temperature (MP −39 °C).

Shiny lustre. Free electrons reflect light efficiently.

An alloy is a mixture of a metal with one or more other elements (often metals, sometimes carbon). Examples:

• Brass = copper + zinc. Used for instruments, fittings.
• Bronze = copper + tin. Used in ship propellers (resists corrosion).
• Steel = iron + carbon (and other elements). Used in buildings, cars.
• Stainless steel = iron + chromium + nickel. Used in cutlery, surgical tools.
• Solder = tin + lead (lead-free versions now common). Used to join electronic components.

Why alloys are usually harder than pure metals. Different-sized atoms disrupt the regular layers. When you try to bend or hammer the metal, the layers can no longer slide past each other smoothly — they get stuck on the misfit atoms. Result: alloys are harder, stronger and often less easily corroded than pure metals.

MYP criterion D often asks you to evaluate which alloy fits a job — e.g. why we use steel rather than pure iron in buildings (steel is much harder and tougher).