Ionic bonds

Reactive atoms that are close to filling their valence shells will pull on the valence electrons of nearby atoms with force. This property is called electronegativity. The closer an atom is to filling its valence shell, the more electronegative that atom is. For example, chlorine (Cl) has an atomic number of 17. The valence shell of Cl contains seven out of a total possible eight electrons. Cl requires only one electron to fill its valence shell and it is very electronegative compared to sodium (Na), for example. Na has an atomic number of 11 and its valence shell contains one out of a possible eight electrons. Therefore, Cl will pull on the single valence electron of Na with force. Na will transfer its valence electron to Cl, resulting in two ions: Na⁺ because Na has transferred a valence electron to Cl and Cl^– because it has gained an electron. The two oppositely charged ions are attracted to one another. The resulting electrostatic attraction between Na⁺ and Cl^– is called an ionic bond and the resulting compound is sodium chloride (NaCl).