Quick questions on Metallic bonding and the properties of metals (QCE Chemistry Unit 1)

Each metal atom donates its valence electrons to a shared pool. What remains is a cation core (the nucleus plus inner-shell electrons). The cores arrange in a regular close-packed lattice. The valence electrons are not localised to any one bond or atom; they roam throughout the lattice, free to move under an applied field.

Two factors govern the strength of the attraction:

Electrical conductivity. The delocalised electrons move freely under an applied potential difference, carrying current through the metal. Conductivity is high in both the solid and molten states, because the electron sea persists. (This contrasts with ionic compounds, which conduct only when molten or dissolved.)

An alloy is a mixture of two or more elements, at least one of which is a metal, in which the components are not chemically bonded but share the same lattice. Substitutional alloys (similar-sized atoms swap into the lattice; e.g. brass = Cu + Zn) and interstitial alloys (smaller atoms fill gaps; e.g. steel = Fe + C) usually have modified properties (harder, less ductile) than the pure metal.

The four-category comparison is a standard QCAA EA Paper 1 short response.

The delocalised electrons move freely under an applied potential difference, carrying current through the metal. Conductivity is high in both the solid and molten states, because the electron sea persists. (This contrasts with ionic compounds, which conduct only when molten or dissolved.)

Delocalised electrons also transport kinetic energy: a hot region of the lattice transfers energy to the electrons, which carry it rapidly to cooler regions. Metals therefore conduct heat as well as charge.

Under stress, planes of cations can slide over one another. The non-directional electron sea immediately readjusts to maintain bonding between the cations in their new positions. So a metal can be hammered into thin sheets (malleable) or drawn into wires (ductile) without fracturing.

The delocalised electrons absorb and re-emit photons across a broad range of visible wavelengths, giving a freshly cut metal surface its characteristic shiny appearance.

Cation cores pack closely in characteristic structures (face-centred cubic, body-centred cubic, hexagonal close-packed), so most metals are dense compared with molecular solids.

As shown in the table above, melting points vary by orders of magnitude depending on charge, electron count and ion size.

Metals do not dissolve in water in the same sense as ionic compounds (the electron sea is not solvable). Some metals react with water (Group 1 vigorously; Group 2 modestly), but this is reaction, not dissolution.

They contain cations, not free ions in motion. Conductivity is carried by the delocalised electrons, not by the cations.

It is comparable in strength to ionic bonding for many metals; transition metals exceed most ionic compounds in melting point.

Delocalised does not mean weakly held; it means not localised between two specific atoms. The electron sea is held tightly to the lattice overall.