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Lewis Dot Structures

Forming a chemical bond (ionic and covalent) involves either electron transfer or sharing of electrons. One way to visualize valence shell electrons in a chemical bond is the use of Lewis dot structures. This concept was introduced by Gilbert N. Lewis in 1916.

In Lewis structures, every valence shell electron is illustrated as a single dot. Lone electron pairs are shown as two dots around the element symbol. Sometimes a line is used to indicate a shared or lone pair of electrons.

Examples of the Lewis dot structure for, A - the formation of the ionic bond between Potassium (K) and Chlorine (Cl), and B - for the formation of a covalent bond between two Chlorine atoms: Reaction A is the formation of potassium chloride, K C l. On the left are the reactants, a potassium atom, and a chlorine atom. The potassium atom has 1 valence electron, shown by one dot next to the K. The chlorine atom has 7 valence electrons, shown by the 7 dots around C l. In step 1, potassium donates its 1 electron to chlorine. The products of step 1 are a potassium cation and a chlorine anion. Both ions have a complete octet of electrons. In step 2, the ions react together to form potassium chloride, an ionic compound. Reaction B is the formation of a chlorine molecule, C l 2. On the left are the reactants, 2 chlorine atoms. Both chlorine atoms have 7 valence electrons, shown by the 7 dots around C l. In step 1, the chlorine atoms share an electron with each other so they gain a full octet. The product of step 1 is two chlorine atoms close together with 2 electrons forming a bridge between them. Each chlorine has 6 electrons and 2 shared electrons. In step 2, the 2 electrons which bridge the chlorines changes into a single bond. The product of step 2 is a chlorine molecule, C l 2.

Figure 1: Lewis structures in the formation of KCl and Cl2

Learn how to draw the Lewis structures