Pub. date: 2008 | Online Pub. Date: April 25, 2008 | DOI: 10.4135/9781412963893 | Print ISBN: 9781412958783 | Online ISBN: 9781412963893| Publisher:SAGE Publications, Inc.About this encyclopedia
CHEMISTRY IS THE academic discipline concerned with the study of the composition, structure, properties, and speed of change of matter. The main building blocks of matter of interest to the chemist are elements, atoms, and molecules. A chemical element is a pure substance comprised only of one type of atom. The atom is the smallest unit of an element and is comprised of subatomic particles called protons (positively charged), neutrons (no charge), and electrons (negatively charged). The neutrons and protons reside in the central core of the atoms called the nucleus, whereas the electrons are smaller and free moving. The number of electrons in a given atom balances the protons, and this number is characteristic of any atom of a given element. Dmitri Mendeleev, a Russian chemist, produced the first periodic table in 1869. In this table, elements are arranged in increasing order of the number of protons and are ...