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Covalent Bonds
COVALENT BONDS
As we have talked about, covalent bonds are those that involve the sharing of electrons between atoms of the same molecule. Glucose is a sugar that is involved in multiple covalent bonds. This is also true of the bonding in water. There are orbitals around each atom that contain electrons. In covalent bonding, the atoms form a new orbital that contains the shared electrons. Figure 4 shows the covalent bonding seen in the methane molecule, which is an organic molecule not seen in most organisms:
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Figure 4.
Covalent bonding changes the characteristics of the molecule. At normal room temperature and normal atmospheric pressure, covalent molecules may be solids, liquids, and gases. Ionic compounds are instead only solids at room temperature and pressure. Covalent compounds do not conduct electricity when dissolved in water. Compared to covalently bonded substances, ionic substances have a very high melting and boiling points.
You should know that covalent bonds can be single bonds or multiple bonds. Think of saturated fats, which contain only single bonds, and unsaturated fats, which have double bonds. Single bonds or sigma bonds are strong bonds, involving the sharing of a single pair of electrons. A sigma bond is seen in the bonds between oxygen and hydrogen in water or between two hydrogen atoms in the making of H2 or hydrogen gas.
Double bonding in covalently bonded molecules involves the sharing of four electrons, while triple bonding involves the sharing of six electrons in sigma and pi orbitals. These bonds will make the connection between two atoms stronger. There is mixing of orbitals into hybrid orbitals that what are called “hybrid orbitals”. Multiple bonds always contain a single sigma bond plus other pi bonds between the atoms. Figure 5 shows what these bonds look like:
Figure 5.
Covalent bonds are named according the bond strength or the energy it takes to break the bond. There is more energy in the bonding between two oxygen atoms in O2 gas than there is in the bonding between two hydrogen atoms in H2 gas. Double bonds are stronger than single bonds and triple bonds are the strongest. The double bond strength of O2 is about 497 kilocalories per mole, while the triple bond strength of N2 is about 945 kilojoules per mole.
