Covalent Bonds between Different Atoms

Now that we have looked at electron sharing between atoms of the same element, let us look at covalent bond formation between atoms of different elements. Consider a molecule composed of one hydrogen atom and one fluorine atom:

Each atom needs one additional electron to complete its valence shell. By each contributing one electron, they make the following molecule:

In this molecule, the hydrogen atom does not have nonbonding electrons, while the fluorine atom has six nonbonding electrons (three lone electron pairs). The circles show how the valence electron shells are filled for both atoms.

Use Lewis diagrams to indicate the formation of the following:

1. Cl₂
2. HBr

Solution

a. When two chlorine atoms form a chlorine molecule, they share one pair of electrons. In Cl₂ molecule, each chlorine atom is surrounded by an octet number of electrons.

The Lewis diagram for a Cl₂ molecule is similar to the one for F₂ (shown above).

b. When a hydrogen atom and a bromine atom form HBr, they share one pair of electrons. In the HBr molecule, H achieves a full valence of two electrons (duet) while Br achieves an octet. The Lewis diagram for HBr is similar to that for HF shown above.