Know which types of elements generally form covalent bonds. Covalent bonds are formed between nonmetals, which are mostly located on the right side of the periodic table. Hydrogen, which is located in the top left corner, is also an element that is involved in covalent bonding. An example of a covalent bond is CH4, or methane.
Memorize the diatomic gases. The diatomic gases consist of two atoms of the same element that form a covalent bond. Most of them are in group 17 of the periodic table: I2, or iodine gas; Br2, or bromine gas; Cl2, or chlorine gas; and F2, or fluorine gas. The other diatomic gases are H2, or hydrogen, oxygen, or O2, and nitrogen, or N2.
Determine whether or not the compound can conduct electricity. Often, such information may be provided in a lab manual. If the compound can conduct electricity in the liquid phase, then it is probably ionic, and not covalent. Covalent compounds are not good conductors of electricity in the solid, liquid or gas phases.
Analyze the physical properties of the compound. The boiling point and the melting point are physical properties that are often provided in a science book or lab manual. If the compound has a low boiling point and melting point, then it is probably covalent. If not, then it is probably ionic.
Find the difference in electronegativity of the elements that form the compound. The electronegativity is a value that is assigned to an element to represent how tightly an element will pull in electrons. If the difference in electronegativity is greater than 1.9, then the compound is ionic, but if the difference in electronegativity is 1.9 or lower, then compound is covalent. An example is HCl. The electronegativity of Cl is 3.0, and the electronegativity of H is 2.1. The compound is covalent because 3.0 ' 2.1 = 0.9.