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	/ˈhaɪdrɵdʒɪn/ HYE-dro-jin
Element category	nonmetal
Group, period, block	1, 1, s
Standard atomic weight	1.00794(7) g·mol−1
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·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
Specific 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
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
Thermal conductivity	(300 K) 0.1805 W·m−1·K−1
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

Hydrogen is a chemical element. Its atomic number is 1, which makes it the simplest, known element in the entire universe.

Hydrogen in nature

In its pure form on Earth, hydrogen is usually a gas. Hydrogen is also a part of water. However, a water molecule is actually made of two hydrogen atoms and one oxygen atom, connected together. Hydrogen is important because it is the fuel that powers the Sun and other stars. Hydrogen takes up about 75% 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 which are heavier types of the Hydrogen atom, they are called: deuterium and tritium. These other types of Hydrogen are important in nuclear energy.

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 gas element in the Universe
• It explodes when it touches a flame.

History of Hydrogen

The name "hydrogen" comes from the Greek word for water, 'υδορ (pronounced /HEEW-dor/).

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

Uses of Hydrogen

Hydrogen as fuel (fusion)

Scientists believe atoms are made of protons, neutrons and electrons. From a physics point of view, hydrogen has one proton, and its variants (atoms that are very like hydrogen), deuterium and tritium, also have neutrons.

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 nuclear power stations, is that no waste is produced, and no toxic fuel like uranium is needed. There is a lot of deuterium in seawater. There is more than 600 million tons of hydrogen undergoing fusion every second on the sun.

Burning Hydrogen

1. Water can be easily broken down into hydrogen and oxygen with electricity, but it takes a lot of electricity to get a usable amount of hydrogen.

2. Burning hydrogen combines with oxygen molecules to make steam (pure water).

3. A fuel cell combines hydrogen with an oxygen molecule releasing an electron as electricity.

Hydrogen power grid

For these reasons, many people believe hydrogen power will eventually replace technologies such as diesel-electric engines and biodiesel fuel.

But it is not correct to see hydrogen as a fuel if it is used in a fuel cell. It is more of a replacement for the power grid. Such a grid and infrastructure with new vehicles might be first made in Iceland, a country that has much free geothermal energy and is quite small. Because it imports all fossil fuel, it would help Iceland to completely stop using it. The huge advantage of hydrogen is that when burnt in an engine or in a fuel cell, there is no pollution - just a small amount of water.

If we did move to a hydrogen economy where could the hydrogen come from? Well, there are many places - it can be extracted from water (but this of course will use more energy than you would get back by using it in a fuel cell or an engine). It can be extracted from various types of plant material - corn is possible, though pretty inefficient. Generally it is probably better to refine such material into a more conventional fuel like ethanol.