The Physical & Chemical Properties of Hydrogen


Hydrogen is the most abundant element in the universe and also the lightest. It is one of two elements that make up water, which is not surprising since it is named for the Greek words for "water former." It was discovered in 1671 by Robert Boyle.

Basic Physical Properties

  • The most prevalent physical property of hydrogen is its atomic mass, which is 1.007825 grams/mol. Hydrogen has one proton and one electron, but it has three different isotopes. Hydrogen is a gas at normal atmospheric conditions and, like helium, is much lighter than air. It is highly flammable as well as completely colorless. It has a melting point of - 259.2 Celsius and a boiling point of -252.8 Celsius.

Important Chemical Properties

  • Hydrogen's electronegativity is 2.1 and first ionization energy is 1311 kJ/mol. Hydrogen can form covalent bonds, but it has a specific bond that only it can form known as the hydrogen bond. It can also form a bond that can sometimes be easily broken--this is how acids are formed.

Modeling This Atom

  • Hydrogen is the most basic atom and has therefore been used as a model to accurately predict atomic behavior. The Bohr model of the atom was the first widely accepted model, and it was about the hydrogen atom. It placed the electron that spins around the proton as specified levels that are quantized. This lead to the beginning of quantum mechanics. To jump between levels, the electron simply needs to absorb or emit energy is discrete amounts.

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