Name       : Hydrogen
Symbol     : H
Atomic #   : 1
Atom weight: 1.00794
Melting P. : -255.34
Boiling P. : -252.87
Oxidation  : -1, +1
Pronounced : Hi-dreh-jen
From       : Greek hydro + genes, "water generator"
Identified : Henry Cavendish in 1766
Appearance : Colorless, odorless, tasteless gas
Note       : Lightest and simplest element

[Properties]

  Hydrogen is chemically unique in a number of ways.  Among these unique 
features is its ability to form compounds by giving up an electron or 
acquiring one.  Elements that give up electrons to form compounds are 
considered electropositive and appear at the left side of the periodic 
chart of the elements.  On the other hand, elements that gain electrons
to form compounds are called electronegative elements, and appear near
the righthand side of the periodic chart.  Hydrogen is the one and only
element that can do both; it can be placed in Group IA (electropositive)
or Group VIIA (electronegative).  No other element has an ambiguous
position on the periodic chart.  Most periodic charts show hydrogen in
its IA position.  A few show it in the VIIA position as well.
  Hydrogen tends to be diatomic.  This means the molecules are composed of 
two atoms.  There are two types of Hydrogen molecules, ortho-hydrogen and 
para-hydrogen.  In the ortho-hydrogen molecule, the two protons spin in the 
same plane; in the para-hydrogen moelcule, the spins are in opposite plane.  
This affects the magnet properties and electronic band spectra of the 
molecules.
