In chemistry, a single bond is one type that occurs between two atoms that join together. Where the atoms join is the bond. If the atoms are the same, then they are referred to as a molecule, and if the atoms are different, then they are referred to as a compound. The atoms can be joined by a single bond, a double bond and even a triple bond.
The number of electrons found in the outer most shell around an atom is what determines how it reacts when it comes in contact with another atom. Sharing or transferring electrons between atoms is what creates a chemical bond. Atoms are the most stable, or non-reactive, when they have an outer shell that is full. For a single bond to be created, only one pair of electrons is involved. Two and three electrons are required for double and triple bonds, respectively.
There are three different types of chemical bonds that occur. They occur in different situations and result in molecules and compounds with different properties. The three types of chemical bonds that can result between atoms are: ionic bonds, covalent bonds and metallic bonds. All three of these bonds can be single bonds, double bonds or triple bonds.
A single bond that is ionic results when an electron is transferred from a metal to a non-metal. For example, sodium chloride (NaCl) is a compound that contains an ionic single bond between a sodium atom and a chlorine atom. The reason this occurs is that sodium (Na) has one electron in its outer shell that it wants to give away, and chlorine (Cl) has seven electrons, so it needs one to have a full outer shell. When Na and Cl react to form NaCl, the Na atom transfers one electron to the Cl atom. This is the strongest type of chemical bonding.
Covalent single bonds occur when non-metal atoms join with other non-metal atoms. The difference between covalent and ionic bonds is that the atoms share electrons when a covalent bond is formed. Covalent bonding occurs when there are no metal atoms available to bond with the non-metals. Covalent single bonds are much weaker than ionic single bonds because no electrons are transferred. Examples of single covalent bonds include hydrogen chloride (HCl) and the bonds found in a water molecule — H2O, or two hydrogen atoms attached by a single bond to an oxygen atom.
Metallic bonding occurs between metal atoms, which all have either one, two or three electrons in their outer shells. This type of bond results from metal atoms pooling electrons that the metal atoms can then share. The unique properties of metals and metal mixtures, or alloys, are due to the pool of electrons that is holding them together.