Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 51

A useful guideline is the octet rule. The basis of this rule is that the unreactive nature of the inert gases in Group VIII of the periodic table is related to their outermost electron shell composed of eight electrons, except for helium that has two electrons in its outer shell. The electron configuration of argon (Ar), for example, written as 1s²2s²2p⁶3s²3p⁶, has two electrons in the 3s subshell and six in the 3p subshell, making eight electrons in the outermost shell. According to the octet rule, when two atoms combine to form a molecule, they do so in a manner to form a complete octet in their outermost shell as far as possible. Then the electron configuration of each atom will correspond to that of its closest inert gas in the periodic table. The octet rule is illustrated for the sodium chloride (NaCl) and methane (CH₄) molecules.