Periodic Table of Elements




Hydrogen was first discovered in 1766 by English chemist and physicist Henry Cavendish. French chemist Antoine Lavoisier named it as hydrogen. The word hydrogen comes from two Greek words, meaning "water-forming".

  • Hydrogen is the first element in the periodic table.
  • Hydrogen has simplest atomic structure among all the elements.
  • It is lightest gas and has higher rate of diffusion.
  • It forms more compounds than any other element.

Name: Hydrogen
Symbol: H
Atomic number: 1
Atomic weight: 1.008
State: gas
Group, period, block: 1, 1, s
Color: Colorless
Classification: Non-metallic
Electron configuration: 1s1

Physical Properties

Density: (0 C, 101.325 kPa) 0.08988 g/L
Melting point: 14.01 K,-259.14 C,-434.45 F
Boiling point: 20.28 K,-252.87 C,-423.17 F

Atomic Properties

Oxidation states: 1, -1
Electronegativity: 2.20 (Pauling scale)
Ionization energies: 1st: 1312.0 kJmol-1
Covalent radius: 315 pm
Van der Waals radius: 120 pm
  • H
  • Electron Configuration


There are three isotopes of hydrogen. Since the isotopes of hydrogen has same electron configuration, they have similar chemical properties. However, they differ in reactivity.

  • Protium
  • Deuterium
  • Tritium


  • Protium atom contains one proton and one electron.
  • It has no neutrons in its nucleus.
  • About 99.98% of the hydrogen in nature is protium.
  • atomic mass : 1
  • atomic number : 1
  • symbol : 1H1


  • Deuterium atom contains one proton and electron and one neutron.
  • About 0.015% of the hydrogen in nature is deuterium.
  • atomic mass : 2
  • atomic number : 1
  • symbol : 1H2 or D


  • Tritium atom contains one proton and electron and two neutrons.
  • It is radioactive isotope.
  • It emit low energy harmless β-particles.
  • Half-life of tritium is 12.33 years.
  • There are only very small traces of tritium in nature.
  • Tritium is used as traces in the study of mechanism of reaction.
  • atomic mass : 3
  • atomic number : 1
  • symbol : 1H3 or 1T3


  • Hydrogen is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms.
  • Hydrogen gas is less abundant in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases.
  • Hydrogen is the third most abundant element on the Earth's surface, mostly in the form of chemical compounds such as hydrocarbons and water.