Hydrogen as an element
Hydrogen is the most plentiful element in the universe, although it only makes up .14%
of the earth's surface. However, because it is part of water (H2O) when it burns by
combining with oxygen (explained later in the compound tab), it makes up 40% of the
content of the earth. Most is found in the vast oceans and waterways. In fact the
Greeks gave it its name, which means "maker of water."
Hydrogen, as an element, is very simple, consisting of two parts: a positively charged
nucleus (shown as red - consisting of protons and neutrons) with a negatively charged electron (shown as blue)
rotating around it, much like the moon orbits the earth.
Paracelesus discovered hydrogen in the 1500s, but not until 1766, did Henry Cavendish
discover that it was a separate gas. Until then, the explosive reaction and the
chemistry were not clearly defined.
The hydrogen element is called a hydrogen "atom." When two hydrogen atoms join together
a weak bond forms (H2) to form a hydrogen "molecule." The propensity for two hydrogen
atoms to bond is so weak that they repel more than attract, so that rather than give
off heat, the coming together to form a molecule actually cools (removes heat).
Molecules, then, are two or more atoms joining together to form a bond.
The bonding occurs by the atoms sharing electrons (they orbit the nucleus if more than
one atom). Because of differing atomic structures, elements have different bonding
strengths. The reaction where two hydrogen and one oxygen atoms come together to form
water produces the most heat (btus) of any because the strong electronegativities
involved.
Because energy levels (both to separate the atoms and in the emissions given off in
joining them) could be measured (quantified), the mechanical process has been known as
"quantum" mechanics.
Electrons move in fixed orbits. As more electrons are added to atoms, the orbits fit
patterns (see below). When energy is added, the orbits change and the electrons move
further from the nucleus.
The number of bonds that an atom can form with other atoms is called valance, a term
invented by scientists in 1868.
In the next section, we'll consider how atoms combine with hydrogen to form compounds.
As with the carbon discussion earlier, the properties of the compounds differ from those
of the element.
