The number of protons or the number of electrons in an atom in its normal state is called the atomic number and is denoted by Z. The nucleus of every element contains Z protons and some number of neutrons. The electrons, having the same charge as a proton but of opposite sign, nullify the charge of the protons in the nucleus, making the net electric charge of an atom of an atom to be zero. The chemical properties of an atom are determined principally by interactions involving the outermost electrons. One can understand all regularities in chemical behavior exhibited by the periodic table of elements on the basis of electron configurations. The similarity of elements in each group of the periodic table reflects the corresponding similarity in electronic configuration.
