What Are Non-Metals?
Non-metals are elements found on the right-hand side of the periodic table (with the exception of hydrogen, which is at the top left). There are about 18 non-metal elements, far fewer than metals, but they include some of the most important elements for life on Earth.
Non-metals include: hydrogen (H), carbon (C), nitrogen (N), oxygen (O), phosphorus (P), sulfur (S), chlorine (Cl), and the noble gases.
Physical Properties of Non-Metals
| Property | Description |
|---|---|
| State at room temp. | Many are gases (O₂, N₂, Cl₂); a few are solids (S, C); bromine is a liquid |
| Conductors of heat/electricity | Generally poor conductors (insulators) — except graphite (a form of carbon) |
| Solid non-metals | Brittle — they crack and crumble rather than bending |
| Appearance | Dull (not shiny) when solid |
| Melting/boiling points | Generally low (especially for non-metal gases) |
| Density | Generally low |
Graphite, a form (allotrope) of carbon, is unusual — it is a non-metal but conducts electricity. Its carbon atoms are arranged in flat layers that can slide over each other, and electrons can flow freely between the layers. This is why graphite is used in pencils and as electrodes in electrolysis.
Forms of Carbon — Allotropes
Carbon is a fascinating non-metal that exists in different structural forms called allotropes:
- Diamond: carbon atoms in a strong 3D lattice — extremely hard, transparent, excellent insulator.
- Graphite: carbon atoms in stacked layers — soft (slippery layers), black, conducts electricity.
- Graphene: a single layer of graphite — incredibly strong and a superb conductor.
Despite being made of the same atoms, these forms have very different properties because of their different structures.
Chemical Properties of Non-Metals
Non-metals react with metals to form ionic compounds (salts). For example:
- Sodium (metal) + Chlorine (non-metal) → Sodium chloride (NaCl)
- Iron (metal) + Sulfur (non-metal) → Iron sulfide (FeS)
Non-metals also react with oxygen to form acidic oxides (e.g. CO₂, SO₂), unlike metals which form basic oxides.
Carbon and hydrogen are the two most important non-metals for living things. Carbon is the backbone of all organic molecules — carbohydrates, fats, proteins, and DNA all contain carbon chains. Hydrogen is the most abundant element in the universe and is essential in water and organic compounds.
Importance of Non-Metals
| Non-metal | Importance |
|---|---|
| Oxygen (O₂) | Needed for respiration and combustion |
| Carbon (C) | Backbone of all organic (living) chemistry |
| Nitrogen (N₂) | 78% of air; needed to make proteins |
| Phosphorus (P) | Needed in bones, teeth, DNA |
| Sulfur (S) | Used to make sulfuric acid; in proteins |
| Chlorine (Cl₂) | Water purification; disinfectants |
Real world: Oxygen for respiration and combustion
Every breath you take delivers O₂ to your blood. Oxygen supports the combustion of fuels — without it, nothing burns. Hospitals use pure oxygen in ventilators. Oxy-acetylene welding torches burn acetylene gas in pure oxygen to reach temperatures above 3,000 °C — hot enough to cut through steel — because pure O₂ burns much more intensely than air.
Real world: Carbon in pencils and diamonds
Graphite (a form of carbon) is used in pencil "lead" — the layers of carbon slide off onto paper as you write. Diamond (another form of the same carbon atoms, arranged differently) is the hardest known natural material and is used in drill bits and cutting tools. Both are pure carbon, just with different atomic arrangements.
Real world: Chlorine purifying water
Chlorine gas (Cl₂) is added to tap water and swimming pools in small, safe amounts to kill harmful bacteria and viruses. It works by oxidising the cell membranes of microorganisms. Without chlorine treatment, waterborne diseases like cholera and typhoid would be far more common. Chlorine is also the basis of household bleach.
Where do you see this in real life? The oxygen you breathe, the graphite in your pencil, the nitrogen that makes up 78% of the air, the chlorine in your tap water — non-metals are everywhere, even if you cannot see them.
Practice Problems
A non-metal solid is described as brittle and a poor conductor of electricity. Would it be a good material for an electrical wire? Explain.
Show answer
Diamond and graphite are both made entirely of carbon atoms. Why do they have such different properties?