Non-Metals

The non-metals occupy the upper right portion of the periodic table. Despite being fewer in number than the metals, non-metals are arguably the most important elements for life and for the chemistry of our planet. They form the molecules of the atmosphere, the compounds of living organisms, and the backbone of organic chemistry.

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Overview

Non-metals share several general properties:

• Poor conductors of heat and electricity (insulators)
• Low melting and boiling points — many are gases at room temperature
• Brittle as solids (they shatter rather than bend)
• High electronegativity — they tend to gain electrons to form negative ions (anions) or share electrons in covalent bonds
• Varied appearances — gases (O₂, N₂), liquids (Br₂), and solids (C, S, P) at room temperature

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The Reactive Non-Metals

Element	Symbol	Atomic Number	Group	State at 25 °C
Hydrogen	H	1	1	Gas
Carbon	C	6	14	Solid
Nitrogen	N	7	15	Gas
Oxygen	O	8	16	Gas
Phosphorus	P	15	15	Solid
Sulphur	S	16	16	Solid
Selenium	Se	34	16	Solid

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Hydrogen (H, Z = 1)

• The lightest and most abundant element in the universe — makes up about 75% of all baryonic matter
• Exists as diatomic molecules (H₂) under standard conditions — a colourless, odourless gas
• Burns in air to produce water: 2H₂ + O₂ → 2H₂O
• Used in the Haber process to manufacture ammonia (NH₃) for fertilisers
• Hydrogen fuel cells generate electricity with water as the only by-product — a promising clean energy technology
• Liquid hydrogen is used as rocket fuel (e.g. in the Space Shuttle main engines)
• Isotopes: protium (¹H, no neutrons), deuterium (²H, one neutron), tritium (³H, two neutrons — radioactive)
• Hydrogen bonds (between H bonded to N, O, or F and a nearby electronegative atom) are crucial for the structure of water, proteins, and DNA

Carbon (C, Z = 6)

• The backbone of all known life — organic chemistry is the chemistry of carbon compounds
• Has four valence electrons, allowing it to form four covalent bonds and create an enormous diversity of molecules
• Forms more compounds than any other element — over 10 million known organic compounds

Allotropes of carbon:

Allotrope	Structure	Properties
Diamond	3D tetrahedral network	Hardest natural substance, transparent, electrical insulator
Graphite	Layered hexagonal sheets	Soft, slippery, electrical conductor (along layers)
Graphene	Single layer of graphite	Strongest known material, excellent conductor, flexible
Fullerenes	Spherical or tubular cages (e.g. C₆₀)	Unique chemical properties, used in nanotechnology
Carbon nanotubes	Rolled graphene cylinders	Extremely strong, good conductors, used in composites

• Diamond is used in cutting tools, jewellery, and high-pressure experiments
• Graphite is used in pencils, lubricants, and as electrodes
• Carbon dioxide (CO₂) is a greenhouse gas; carbon monoxide (CO) is a toxic gas
• Activated carbon is used in water and air filtration
• Carbon-14 dating is used to determine the age of archaeological artefacts

Nitrogen (N, Z = 7)