Hydrogen

Hydrogen is the lightest chemical element (symbol H) with an atomic number of 1 and atomic weight of 1.00794. Molecular hydrogen (H2) is a colourless, odourless and flammable gas at room temperature.

General

Name, symbol, number

hydrogen, H, 1

Chemical series

nonmetals

Group, period, block

1, 1, s

Appearance

colorless

Standard atomic weight

1.00794(7)g·mol^-1

Electron configuration

1s1

Electrons per shell

Physical properties

Phase

gas

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)

Triple point

13.8033 K (-259°C), 7.042 kPa

Critical point

32.97 K, 1.293 MPa

Heat of fusion

(H2) 0.117 kJ·mol^-1

Heat of vaporization

(H2) 0.904 kJ·mol^-1

Heat capacity

(25 °C) (H2)
28.836 J·mol^-1·K^-1

Vapor pressure
P/Pa	1	10	100	1 k	10 k	100 k
at T/K					15	20

Atomic properties

Crystal structure

hexagonal

Oxidation states

1, ^-1
(amphoteric oxide)

Electronegativity

2.20 (Pauling scale)

Ionization energies

1st: 1312.0 kJ·mol^-1

Atomic radius

25 pm

Atomic radius (calc.)

53 pm

Covalent radius

37 pm

Van der Waals radius

120 pm

Miscellaneous

Thermal conductivity

(300 K) 180.5 m W·m^-1·K^-1

Speed of sound

(gas, 27 °C) 1310 m/s

CAS registry number

1333-74-0

View the Periodic Table...

View the List of Elements...

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