Hydrogen and Clean Fuels
Hydrogen and Clean Fuels Basics
This section addresses the following topics:
What is hydrogen?
Hydrogen Molecule
 Hydrogen or H is the simplest element in nature. The hydrogen atom consists of one positively charged proton and one negatively charged electron bound together by their electrical attraction for each other (physicists call this the electrostatic force). The illustration at right is an artist’s conception of a hydrogen atom; quantum physics shows that the electron does not appear in one place, but behaves as a spherically symmetric “electron cloud” around the proton or nucleus. The inset shows a magnified view of the proton, which is actually much smaller than the atom. Hydrogen atoms are very reactive and easily combine with each other to form molecular hydrogen or H2; as a result atomic hydrogen is not found in nature at normal temperatures and pressures. Molecular hydrogen consists of two hydrogen atoms bound together by sharing their electrons. The lower illustration at right shows how the two electron clouds overlap in a hydrogen molecule. Molecular hydrogen or H2 is usually implied when the term hydrogen is used. Hydrogen atoms and molecules are the most studied and well-understood materials in nature from a scientific standpoint, serving in roles as varied as test cases for validation of quantum physics theories to spectral standards for measurement of the speed of distant galaxies.
 Molecular hydrogen is a stable gas and can be stored for long periods in pressurized bottles. However, hydrogen has such a low density and is so buoyant that, when released in the open, it rapidly rises to the top of the Earth’s atmosphere. It also easily reacts with other elements such as oxygen. As a result, only very small amounts are found in the lower atmosphere or in the Earth’s crust, and so molecular hydrogen is not a useful source of fuel. While hydrogen is the most plentiful element in the universe, being found in all stars and in interstellar space, almost all hydrogen in the Earth exists in chemical combination with other elements, such as oxygen in water, or carbon in fossil fuels such as oil, natural gas, or coal. Other unique or significant attributes of hydrogen include:
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- Two hydrogen atoms combine with one oxygen atom to form a molecule of water, one of the most basic chemical compounds in our lives.
- Combined with carbon, hydrogen helps form the basic structures of life as we know it, including nucleic acids (DNA and RNA) and proteins. Fossil fuels come from ancient life forms.
- Again combined with carbon, hydrogen is a constituent of many plastics and chemicals that we use in everyday life.
- Hydrogen nuclei (protons) furnish the fuel for the sun and all the stars in the universe, and for potential nuclear fusion energy sources here on Earth.
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