Valences

Along with carbon, we will also deal with hydrogen, oxygen, nitrogen and the halogens (fluorine, chlorine, bromine and iodine). Let's go through some of the bonding features of each of these elements also. (The properties listed below are summarized in a table at the bottom of the page.)

Again let's start with carbon. Carbon has four unpaired electrons in its outer shell. It needs four electrons to get eight in its outer shell; therefore, it tends to form four covalent bonds. It can form these four covalent bonds to other carbon atoms or to atoms of other elements such as hydrogen, oxygen, nitrogen, or chlorine or a wide variety of others as well. Because it can form four bonds, carbon is said to have a valence of four. It can form single, double or triple bonds.

Hydrogen is quite different. It has one electron in its outer shell and needs only one more to complete its outer shell. So it can form one covalent bond, and it is said to have a valence of one. It can form only single bonds.

Oxygen has six electrons in its outer shell, needs two more, and will form two covalent bonds to get those two additional electrons. Thus, oxygen is said to have a valence of two. Please note the difference between "valence" and "valence electrons". Oxygen has a valence of two, and it has six valence electrons. It can form single or double bonds.

Nitrogen has five valence electrons, five electrons in its outer shell, and needs three electrons to complete that outer shell. It can gain those three through covalent bonds by forming three covalent bonds. So, it is considered to have a valence of three. It can form single, double or triple bonds.

Chlorine is typical of the halogens so I will use it as a specific example of the halogens in general. Everything I say about the bonding of chlorine can be applied to the other halogens as well. Chlorine has seven valence electrons, needs one to fill its outer shell, so chlorine has a valence of one and can form only single bonds.

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E-mail instructor: Eden Francis

Clackamas Community College
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