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General Chemistry - Covalent Bonds

When we say covalent bond, we are talking about a bond in which two atoms share a pair of electrons. The shared electrons revolve around the nuclei of both atoms in the bond. In order to form the pair, each atom contributes one unpaired electron. If an atom has one unpaired electron, it can form one covalent bond. If it has two unpaired, electrons, it can form two covalent bonds. If it has three unpaired electrons, it can form three covalent bonds. 

Think about a molecule of water. The oxygen atom has two unpaired electrons. Each of the hydrogen atoms has one unpaired electron, so the oxygen atom can make two covalent bonds and each of the hydrogen atoms can make one covalent bond. So, remember that the number of covalent bonds an atom can form is equal to the number of unpaired electrons in its outer shell. 

Polar Bonds :
If two atoms form a covalent bond and one of the atoms is more electronegative than the other, the bond will be a polar bond since it is not balanced based on charge. 

Hydrogen Bonds :
A hydrogen bond is an attraction between a hydrogen atom attached to one molecule and a highly electronegative atom in another molecule. Remember that hydrogen bonding typically occurs with oxygen, nitrogen, and fluorine.