The tendency of main group atoms to form enough bonds to obtain eight valence electrons is known as the octet rule. This allows each halogen atom to have a noble gas electron configuration. The other halogen molecules (F 2, Br 2, I 2, and At 2) form bonds like those in the chlorine molecule: one single bond between atoms and three lone pairs of electrons per atom. Each Cl atom interacts with eight valence electrons: the six in the lone pairs and the two in the single bond. A dash (or line) is sometimes used to indicate a shared pair of electrons:Ī single shared pair of electrons is called a single bond. The Lewis structure indicates that each Cl atom has three pairs of electrons that are not used in bonding (called lone pairs) and one shared pair of electrons (written between the atoms). For example, when two chlorine atoms form a chlorine molecule, they share one pair of electrons: We also use Lewis symbols to indicate the formation of covalent bonds, which are shown in Lewis structures, drawings that describe the bonding in molecules and polyatomic ions. The total number of electrons does not change. Cations are formed when atoms lose electrons, represented by fewer Lewis dots, whereas anions are formed by atoms gaining electrons. Likewise, they can be used to show the formation of anions from atoms, as shown here for chlorine and sulfur:įigure 2 demonstrates the use of Lewis symbols to show the transfer of electrons during the formation of ionic compounds. Lewis symbols can also be used to illustrate the formation of cations from atoms, as shown here for sodium and calcium: Lewis symbols illustrating the number of valence electrons for each element in the third period of the periodic table. A Lewis symbol consists of an elemental symbol surrounded by one dot for each of its valence electrons:įigure 1 shows the Lewis symbols for the elements of the third period of the periodic table. We use Lewis symbols to describe valence electron configurations of atoms and monatomic ions. In this section, we will explore the typical method for depicting valence shell electrons and chemical bonds, namely Lewis symbols and Lewis structures. In all cases, these bonds involve the sharing or transfer of valence shell electrons between atoms. Thus far in this chapter, we have discussed the various types of bonds that form between atoms and/or ions. Draw Lewis structures depicting the bonding in simple molecules.Write Lewis symbols for neutral atoms and ions.By the end of this section, you will be able to:
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