Characteristics:
Hydrogen is the simplest element of all, and the lightest. It is also by far the most common element in the Universe. Over 90 percent of the atoms in the Universe are hydrogen.
In its commonest form, the hydrogen atom is made of one proton, one electron, and no neutrons. Hydrogen is the only element that can exist without neutrons.
Hydrogen is a colorless, odorless gas which exists, at standard temperature and pressure, as diatomic molecules, H2.
It burns and forms explosive mixtures in air and it reacts violently with oxidants.
On Earth, the major location of hydrogen is in water, H2O. There is little free hydrogen on Earth because hydrogen is so light that it is not held by the planet’s gravity. Any hydrogen that forms eventually escapes from the atmosphere into space.
Although hydrogen is usually a nonmetal, it becomes a liquid metal when enormous pressures are applied to it.
Such pressures are found within gas giant planets such as Jupiter and Saturn. Jupiter’s high magnetic field (14 times Earth’s) is believed to be caused by a dynamo effect resulting from electrically conducting metallic hydrogen circulating as the planet rotates.