The relative ability of an atom to draw electrons in a bond toward itself is called the electronegativity of the atom. The electronegativities of the main group elements are given in the figure below. When the magnitude of the electronegativities of the main group elements is added to the periodic table as a third axis, we get the results shown in the figure below. There are several clear patterns in the data in the above two figures. Electronegativity increases in a regular fashion from left to right across a row of the periodic table.
Electronegativity decreases down a column of the periodic table.
When the difference between the electronegativities of the elements in a compound is relatively large, the compound is best classified as ionic . NaCl, LiF, and SrBr 2 are good examples of ionic compounds. In each case, the electronegativity of the nonmetal is at least two units larger than that of the metal. We can therefore assume a net transfer of electrons from the metal to the nonmetal to form positive and negative ions and write the Lewis structures of these compounds as shown in in the figure below. These compounds all have high melting points and boiling points, as might be expected for ionic compounds.