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Always an important and interesting element, hydrogen has gathered increased notice in the public eye with the focus on hydrogen fuel cells and hydrogen cars. Surely people long to learn more about this "magic" chemical that will simultaneously help free us from gasoline and pollution.

Hydrogen is the simplest atom, having but a single proton and a single electron. Normally it is found with no neutrons, but isotopes with one (deuterium) and two (tritium - which is radioactive) neutrons are known. Elemental hydrogen consists of two hydrogen atoms, bound together by a single covalent bond. (Hydrogen can only make one bond, since it has but the one electron.)

Hydrogen is the most versatile of all elements. Most elements are readily classified as metal, non-metal, or metalloid. (Each group has a set of general properties.) Not so with hydrogen.

Most periodic tables place hydrogen in the first group. (First element, first group - that seems to make sense.) This group - the alkali metals - does share some chemistry with hydrogen. They all have just one electron in their outermost (or valence) "shell". All will react with electronegative elements to give up that outermost electron, becoming a singly charged positive ion. Hydrogen does this regularly. The hydrogen ion that results is really just a single proton, and is often referred to as such by chemists. The chemistry of the hydrogen ion is of great interest. Most people are familiar with the pH scale - our way of measuring acidity in soils and solutions. The "H" in pH specifically refers to Hydrogen, whose chemical symbol is H. (The "p", if you wondered, is a mathematical function, corresponding to "the negative logarithm of ______", in this case, the activity/concentration of the hydrogen ion in solution.) Solutions with more hydrogen atoms are more acidic. For the record, the hydrogen atom does not exist freely in water, it is always coordinated with water molecules. Sometimes the complex that forms is referred to as the "hydronium ion".

On fewer periodic tables, hydrogen is listed in the seventh group - the halogens. Halogens are non-metals. They are each one electron away from achieving a stable outer shell of electrons. (Hydrogen reaches a full, stable shell once it reaches two electrons.) In the elemental form, each exists as a diatomic molecule, as hydrogen does. Halogens will react with metals to "steal" an electron, acquiring a net charge of negative one. When hydrogen forms an ion in this way, it is referred

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