Metals and non-metals
The periodic table neatly splits into metals (left and centre) and non-metals (top right). The line dividing them is the famous "staircase" through B–Si–As–Te–Po (semi-metals or metalloids sit on the boundary).
Why metals are different
A metal atom has few outer electrons (typically 1–3). It loses these to form positive ions, with a structure of giant lattices held together by metallic bonding (delocalised electrons — see C2.4). This explains every typical metallic property.
Physical properties of metals
| Property | Reason |
|---|---|
| Shiny when polished | Reflect light off the sea of electrons |
| Good conductors of electricity | Delocalised electrons carry charge |
| Good conductors of heat | Delocalised electrons transfer kinetic energy |
| Malleable (can be hammered) | Layers of ions slide over each other |
| Ductile (can be drawn into wire) | Same — layers slide |
| High melting and boiling points | Strong metallic bonds need lots of energy to break |
| Sonorous (ring when struck) | Layers of ions vibrate together |
There are exceptions: mercury is a liquid metal at room temperature; alkali metals are soft and have low melting points.
Physical properties of non-metals
Non-metals are typically:
- Dull / not shiny.
- Poor conductors of heat and electricity (graphite, an exception, conducts because it has delocalised electrons).
- Brittle when solid (don't bend — they break).
- Often have lower melting and boiling points (many are gases, e.g. O₂, N₂; some liquids like Br₂; some low-melting solids).
- Lower density.
Chemical properties
When metals and non-metals react with oxygen:
- Metal oxides are usually basic — they react with acids to form salt and water.
- Non-metal oxides are usually acidic — they react with bases to form salt and water.
This is a clean F/H exam contrast.
Why this difference?
Whether an element is a metal or non-metal depends on its electronic structure:
- Metals have few outer-shell electrons. They lose them to become positive ions, leaving them with a stable noble-gas configuration (one shell less).
- Non-metals have many outer-shell electrons (4–7). They gain electrons (or share them) to fill their outer shell, becoming negative ions or covalent molecules.
This is why metals tend to be on the left (low outer-electron count) and non-metals on the right of the table.
Reactivity series — preview
Metals can be ranked by how readily they react. From most reactive → least reactive:
K, Na, Ca, Mg, Al, C, Zn, Fe, (H), Cu, Ag, Au.
Carbon and hydrogen are non-metals included to compare extraction methods (C4.2). More reactive metals lose electrons more easily.
⚠Common mistakes
- Saying all metals conduct. They do — but graphite (a non-metal) also conducts because of delocalised electrons.
- "Brittle" vs "soft". Brittle = breaks under stress; soft = easily bent or scratched. Some non-metals (sulfur) are soft; many ionic crystals are brittle.
- Treating mercury as a non-metal because it's liquid. It's still a metal — just one with an unusual melting point.
- Mixing up acidic and basic oxides. Metal oxides usually basic; non-metal oxides usually acidic.
Links
Sets up groups (C1.6–8), bonding C2 and chemical reactions C4.
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