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Hydrogen is a colourless, odourless and flammable gas. It is the lightest of all the elements, and was used as the lift gas in early airships until the Hindenburg disaster in 1937, after which it was replaced by helium. Hydrogen is the most abundant element in the universe, but most is in the atomic form and the molecular form is not common. On Earth, molecular hydrogen is produced by some micro-organisms, but most hydrogen exists in combined form in water and organic matter. Hydrogen can be used as a fuel, but it is not an energy source, since the energy it can provide comes from the electrical energy used to produce it by the electrolysis of water.
The atoms in the molecule are connected by a single covalent bond. A covalent bond is formed when atoms share electrons and a single covalent bond has two shared electrons, one contributed by each atom. Because the electrons in the bond are shared equally by the two hydrogen atoms, the molecule does not have an electric dipole.
The type of model shown here, called a ball-and-stick model, is one of several ways of modelling molecules. This type is useful because it clearly shows the geometry of the molecule and the order (single, double or triple) of the bonds. However, because 'sticks' are used to represent bonds, this type of model does not represent the actual shape of the molecule as well as 'space-filling' models do.