Many compounds do not contain ions but instead consist of neutral atoms being involved in covalent bonding (sharing of electrons to create molecular compounds (covalent compounds). Covalent bonding is focused on in more detail in a later section.
Whereas ionic compounds are usually formed when a metal and a nonmetal combine, covalent compounds are usually formed by a combination of nonmetals. Thus, the periodic table can help us recognize many of the compounds that are covalent. We can use the positions of a compound’s elements in the periodic table to predict whether it is ionic or covalent at this point in our study of chemistry.
Predicting the Type of Bonding in Compounds
Predict whether the following compounds are ionic or molecular:
(a) KI, the compound used as a source of iodine in table salt
(b) H2O2, the bleach and disinfectant hydrogen peroxide
(c) CHCl3, the anesthetic chloroform
(d) Li2CO3, a source of lithium in antidepressants
Solution
(a) Potassium (group 1) is a metal, and iodine (group 17) is a nonmetal; KI is predicted to be ionic.
(b) Hydrogen (group 1) is a nonmetal, and oxygen (group 16) is a nonmetal; H2O2 is predicted to be covalent.
(c) Carbon (group 14) is a nonmetal, hydrogen (group 1) is a nonmetal, and chlorine (group 17) is a nonmetal; CHCl3 is predicted to be covalent.
(d) Lithium (group 1) is a metal, and carbonate is a polyatomic ion; Li2CO3 is predicted to be ionic.
Check Your Learning
Using the periodic table, predict whether the following compounds are ionic or covalent:
(a) SO2
(b) CaF2
(c) N2H4
(d) Al2(SO4)3
Answer
(a) covalent; (b) ionic; (c) covalent; (d) both ionic and covalent