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Lanthanides

Actinides

1Reactive Nonmetal

Hydrogen

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Quick Facts

Atomic Number1

Atomic Mass1.008 u

Group1

Period1

Blocks-block

CategoryReactive Nonmetal

State at Room Temp.Gas

Electron Shells1

Physical Properties

Density0.00008988 g/cm³

Melting Point-259.16 °C

Boiling Point-252.87 °C

AppearanceColorless, odorless gas

Crystal StructureHexagonal (solid H₂)

Specific Heat Capacity14.304 J/(g·K)

Thermal Conductivity0.1805 W/(m·K)

Electrical ConductivityNot applicable (insulator as gas)

Heat of Fusion0.117 kJ/mol

Heat of Vaporization0.904 kJ/mol

Atomic Properties

Electron Configuration1s¹

Valence Electrons1

Oxidation States+1, -1

Electronegativity (Pauling)2.20

1st Ionization Energy1312.0 kJ/mol

2nd Ionization EnergyNot applicable

Electron Affinity72.8 kJ/mol

Atomic Radius53 pm

Covalent Radius31 pm

Van der Waals Radius120 pm

Ionic RadiusNot available

Chemical Properties

Highly flammable gas. Reacts explosively with oxygen and vigorously with halogens; forms hydrides with most elements.

Natural Occurrence

The most abundant element in the universe, found mainly in stars as plasma. On Earth it rarely occurs as free H₂ and is found chiefly combined in water and organic compounds.

Discovery & Naming

Discovered ByHenry Cavendish

Year1766

LocationLondon, England

Name OriginGreek 'hydro' (water) and 'genes' (forming) — 'water-forming'

Uses & Applications

Ammonia synthesis (Haber–Bosch process)
Petroleum refining and hydrocracking
Rocket propellant
Hydrogen fuel cells
Hydrogenation of fats and oils

Biological Role

Essential constituent of water and virtually all organic molecules; required for life as we know it.

Isotopes

¹H (Protium)Stable, ~99.98% natural abundance

²H (Deuterium)Stable, ~0.02% natural abundance

³H (Tritium)Radioactive, half-life ≈ 12.32 years

Nuclear Properties

Naturally StableYes

Most Stable Isotope¹H

Half-lifeStable

Decay ModeNone

Safety & Toxicity

Extremely flammable; forms explosive mixtures with air (4–75% by volume). Not toxic, but can act as an asphyxiant by displacing oxygen.

Did You Know?

Hydrogen makes up roughly 75% of the normal matter in the universe by mass, mostly locked inside stars.