Hydrogen
Uploaded by msnarayana on Nov 22, 2012
Hydrogen
1H
-
↑
H
↓
Li
Periodic table
- ← hydrogen → helium
Appearance
colorless gas
Purple glow in its plasma state
Spectral lines of hydrogen
General properties
Name, symbol, number hydrogen, H, 1
Pronunciation /ˈhaɪdrədʒən/ HY-drə-jən[1]
Element category nonmetal
Group, period, block 1, 1, s
Standard atomic weight 1.008(1)
Electron configuration 1s1
1
History
Discovery Henry Cavendish[2][3] (1766)
Named by Antoine Lavoisier[4] (1783)
Physical properties
Color colorless
Phase gas
Density (0 °C, 101.325 kPa)
0.08988 g/L
Liquid density at m.p. 0.07 (0.0763 solid)[5] g·cm−3
Liquid density at b.p. 0.07099 g·cm−3
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
Molar heat capacity (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
Oxidation states 1, -1
(amphoteric oxide)
Electronegativity 2.20 (Pauling scale)
Ionization energies 1st: 1312.0 kJ·mol−1
Covalent radius 31±5 pm
Van der Waals radius 120 pm
Miscellanea
Crystal structure hexagonal
Magnetic ordering diamagnetic[6]
Thermal conductivity 0.1805 W·m−1·K−1
Speed of sound (gas, 27 °C) 1310 m·s−1
CAS registry number 1333-74-0
Most stable isotopes
Main article: Isotopes of hydrogen
iso NA half-life DM DE (MeV) DP
1H 99.985% 1H is stable with 0 neutrons
2H 0.015% 2H is stable with 1 neutron
3H trace 12.32 y β− 0.01861 3He
v ·t ·e· r
Hydrogen is a chemical element with symbol H and atomic number 1. With an average atomic weight of 1.00794 u (1.007825 u for hydrogen-1), hydrogen is the lightest element and its monatomic form (H1) is the most abundant chemical substance, constituting roughly 75% of the Universe's baryonic mass.[7] Non-remnant stars are mainly composed of hydrogen in its plasma state.
At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, highly combustible diatomic gas with the molecular formula H2. Naturally occurring atomic hydrogen is rare on Earth because hydrogen readily forms covalent compounds with most elements and is present in the water molecule and in most organic compounds. Hydrogen plays a particularly important role in acid-base chemistry with many reactions exchanging protons between soluble molecules.
In ionic compounds, it can take a negative charge (an anion known as a hydride and written as H−), or as a positively charged...