Environmental Engineering Reference
In-Depth Information
Introduction to Basic Properties
of Hydrogen
Hydrogen is known as the most abundant element in the universe. It accounts
for about 75% of the known mass of the universe. Hydrogen is a major
element in many known stars and planets. For example, stars, when formed
in the present Milky Way galaxy, are composed of about 71% hydrogen and
27% helium, as measured by mass, with a small fraction of heavier elements
[1]. Stars spend about 90% of their lifetime fusing hydrogen to produce
helium in high temperature and high pressure reactions near the core. Thus,
hydrogen is a critical element for the very existence of the universe.
Both the hydrogen atom (H) and hydrogen molecule (H 2 ) have many
unique chemical and physical properties. Hydrogen is also a major compo-
nent of many important molecules, such as water, hydrocarbons, proteins,
and DNA. It is safe to say that there would be no life if there were no
The atomic hydrogen is the smallest and lightest element. The hydrogen
atom consists of one proton (H + ) and one electron, with no neutrons, and is
usually denoted as 1 H or just H (also named as protium sometimes). Hydro-
gen has two common isotopes, deuterium (D or 2 H) and tritium (T or 3 H),
that contain one and two neutrons, respectively, in addition to the one proton
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