Periodic Table

Quick facts

Atomic mass

1.008

Group

1

Period

1

State (STP)

gas

Electronegativity

2.20

Common ox. states

-1, +1

Properties

Ionization energy

1312.0 kJ/mol

Electron affinity

72.8 kJ/mol

Melting point

13.99 K (-259.2 °C)

Boiling point

20.27 K (-252.9 °C)

How it bonds

Hydrogen has one electron and forms one bond. Almost always covalent — sharing one pair to fill its 1s shell — but with very electronegative partners (F, Cl, O, N) the shared pair drifts so far that the H is effectively H⁺. With reactive metals (Na, Ca) the trade flips and hydrogen pulls the electron in to become H⁻.

Where you meet it

• Build WaterH₂O
• Build AmmoniaNH₃
• Build MethaneCH₄
• Build Hydrogen cyanideHCN
• Build Hydrogen fluorideHF
• Build Hydrogen peroxideH₂O₂
• Build Hydrogen chlorideHCl
• Build FormaldehydeCH₂O
• Periodic Quest challengeunlock card

Deeper

• Reading the periodic table
• Water and the bend
• Single bonds with halogens
• Valence
• Double bonds
• Diatomic elements
• Lone pairs
• Triple bonds