CHAPTER 2 - Atomic Structure

Abstract

Each atom is made up of protons, neutrons, and electrons. These are called fundamental particles and it seemed that all matter is made up from these three basic units, combined first into atoms of the various elements, which in turn combined to give all other substances. The number of protons in an atom is the atomic number and equals the number of electrons. Atoms with atomic numbers from 1 to 92 occur naturally and others with higher atomic numbers have been made artificially by nuclear reactions. The arrangement of the electrons in an atom is determined mainly by the charge on the nucleus and the number of electrons and as these are both equal to the atomic number, all atoms with the same atomic number have the same electron arrangement. The chemical reactions of an atom are determined by the electron arrangement. Therefore, all atoms with the same atomic number are chemically identical. Atoms having the same atomic number are not necessarily identical in mass. Atoms having the same atomic number but different mass numbers are called isotopes. Isotopes are known by the name of the element corresponding to their atomic number. However, they are distinguished by the use of the mass number.