Hydrogen

- ← hydrogen → helium - ↑ H ↓ Li 1H Periodic table
Appearance
Colorless gas with purple glow in its plasma state Spectral lines of hydrogen
General properties
Name, symbol, number	hydrogen, H, 1
Pronunciation	/haɪdrədʒən/ HYE-dro-jin
Element category	nonmetal
Group, period, block	1, 1, s
Standard atomic weight	1.00794(7) g/mol
Electron configuration	1s1
Electrons per shell	1 (Image)
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) g/cm3
Liquid density at b.p.	0.07099 g/cm3
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
Heat of vaporization	(H2) 0.904 kJ/mol
Specific heat capacity	(25 °C) (H2) 28.836 J/(mol·K)
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
Covalent radius	31±5 pm
Van der Waals radius	120 pm
Miscellanea
Crystal structure	hexagonal
Magnetic ordering	diamagnetic
Thermal conductivity	(300 K) 0.1805 W/(m·K)
Speed of sound	(gas, 27 °C) 1310 m/s
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

Hydrogen is a chemical element. Its atomic number is 1, which makes it the simplest known element in the entire universe. Hydrogen is the true primordial substance, the first atom produced after the Big Bang. All chemical elements were formed from hydrogen by the processes of nuclear fusion.

Hydrogen glows purple when it is in plasma state.

Hydrogen in nature

In its pure form on Earth, hydrogen is usually a gas. Hydrogen is also one of the parts that make up a water molecule. Hydrogen is important because it is the fuel that powers the Sun and other stars. Hydrogen makes up about 74% of the entire universe. Hydrogen's symbol on the Periodic Table of Elements is H.

Pure hydrogen is normally made of two hydrogen atoms connected together. Scientists call these diatomic molecules. Hydrogen will have a chemical reaction when mixed with most other elements. It has no color or smell.

Pure hydrogen is very uncommon in the Earth's atmosphere. In nature, it is usually in water. Hydrogen is also in all living things, as a part of the organic compounds that living things are made of. In addition, hydrogen atoms can combine with carbon atoms to form hydrocarbons. Petroleum and other fossil fuels are made of these hydrocarbons and commonly used to create energy for human use.

Hydrogen has two different isotopes, called deuterium and tritium. Like regular hydrogen, they both have only one proton and one electron, but deuterium also has one neutron and tritium has two. These other types of hydrogen are important in nuclear energy and organic chemistry reactions.

Some other facts about hydrogen:

• It is a gas at room temperature
• It acts like a metal when it is solid.
• It is the lightest element in the Universe.
• It is the most common element in the Universe.
• It burns or explodes when it touches a flame.

History of Hydrogen

Hydrogen was discovered in 1671 by Robert Boyle even though many people think it was discovered by Henry Cavendish in 1776.

The word

The name 'Hydrogen' comes from the Greek word for water, 'υδορ (pronounced /HEEW-dor/) and gennen meaning to "generate" as it forms water in a chemical reaction with oxygen.

Uses of Hydrogen

The main uses are in the petroleum industry and in making ammonia by the Haber process. Some is used elsewhere in the chemical industry. A little of it is used as fuel, for example in rockets for spacecraft. Most of the hydrogen that people use comes from a chemical reaction between natural gas and steam.

Nuclear fusion

Nuclear fusion is a very powerful source of energy. It relies on forcing atoms together to make helium and energy, exactly as happens in a star like the Sun, or in a hydrogen bomb. This needs a large amount of energy to get started, and is not easy to do yet. A big advantage over nuclear fission, which is used in today's nuclear power stations, is that it makes less nuclear waste and does not use a toxic and rare fuel like uranium. More than 600 million tons of hydrogen undergo fusion every second on the Sun.

Burning Hydrogen

The electrolysis of water easily breaks water into hydrogen and oxygen, using electricity. Burning hydrogen combines with oxygen molecules to make steam (pure water vapor). A fuel cell combines hydrogen with an oxygen molecule, releasing an electron as electricity. For these reasons, many people believe hydrogen power will eventually replace other synthetic fuels.

Hydrogen can also be used as fuel in a fuel cell, or burned to make heat for steam turbines or internal combustion engines. Hydrogen can be created from many sources such as coal, natural gas or electricity, and therefore represents a valuable addition to the power grid; in the same role as natural gas. Such a grid and infrastructure with fuel cell vehicles is now planned by a number of countries including Japan, Korea and many European countries. This allows these countries to buy less petroleum, which is an economic advantage. The other advantage is that used in a fuel cell or burned in a combustion engine or turbine, there is no pollution. Only water, and a small amount of nitrogen oxides, forms.

Other websites

• Hydrogen -Citizendium