More information Created in 1970 as an agency of the United States federal government, charged with protecting the environment and enforcing environmental laws and regulations.

Elements with even numbers of protons and an even number of neutrons make up about 90% of the earth's crust.

The possible locations around an atom where electrons having specific energy values (quantum number) may be found.

The term shell has been replaced with the term energy levels because the term shell insinuated that electrons circled the atom in fixed orbits like planets circle the sun. Although the term shell is outdated, it is still often used grade school and high school science classes, as its concepts are less intimidating than are the use of terms like quantum number.

A measure of the ability of an atom in a molecule to draw bonding electrons to itself.

This is partially determined by how many electron vacancies are available in an element's filling orbital. A particle of matter that has a negative electric charge of 4.8 Eg or 1/1837 the mass of a proton.

The most electronegative elements are the halogens, which have only one vacancy (i.e. They can be found as a constituent part of an atom orbiting around the nucleus or in the free state.Electrons are arranged around the nucleus of an atom in from one to seven orbitals with the number of electrons in each orbital is strictly limited by the laws of physics.More information The smallest amount of photonic energy necessary to remove an electron from the boundary of an element.One of the 116 presently known substances that cannot be decomposed by chemical reaction into a simpler substance.Elements comprise all matter at and above the atomic level.All elements heavier than lead (Pb) are radioactive and unstable.