Simple Explanation of the Types of Chemical Bond
The Main Ways that Atoms Join Together to Form Molecules
Apr 28, 2009
A chemical molecule is formed when two or more atoms join together. They join either when one or more atoms "donates" electrons to the other(s), in a process called ionic bonding, or when they share electrons, to form a covalent bond. For an explanation of what electrons and atoms are, the article Structure of the Atom is good background.
Ionic Bonding
This type of molecular bond happens when an atom, or group of atoms, "donates" one or more electrons to another atom, or group of atoms. An atom is electrically neutral, but when an atom loses one or more electrons, it is positively charged. It is then called an "ion".
An example of ionic bonding is Sodium Chloride, or table salt. Sodium has one spare electron in the outer shell, and Chlorine has an outer shell that needs one electron to complete it. They can therefore react to form an ionic compound.
Covalent Bonding
A covalent bond is formed when one or more atoms share electrons so that they can each end up with completed outer shells. There are several different types of covalent bond.
Non-Polar Covalent Bonding
This type of chemical bond happens when two atoms from the same element share electrons. Hydrogen gas, for example, is made from molecules that are formed from pairs of Hydrogen atoms. Each hydrogen atom has one electron, but needs two electrons to complete the outer shell. Since each atom has the same "pull" on the electrons, the covalent bond is not biased towards any of the atoms. It is therefore non-polar.
Polar Covalent Bonding
This type of chemical bond happens when atoms share electrons, but one of the atoms takes a larger "share" of the electrons. Hydrogen Chloride molecules are made from one atom each of Hydrogen and Chlorine. Each atom shares one electron with the other. It is polar, because the Chlorine "uses" the two shared electrons more than the Hydrogen does. Most molecules are at least slightly polar.
Dative Bond (aka Coordinate Covalent Bond)
This type of chemical bond is formed when the shared electrons are all provided by one of the atoms in the molecule. A good example is the Ammonium ion. Nitrogen has five electrons in the outer shell, and Hydrogen has one. Ammonia is formed when three Hydrogen atoms combine with one Nitrogen atom to form a molecule. There are therefore three pairs of shared electrons plus one pair of electrons provided solely by the Nitrogen. In a solution of water, however, a Hydrogen ion can "tag" onto the pair of electrons provided by the Nitrogen, to form the Ammonium (NH4+) ion. (Note that Ammonium is Ammonia [NH3] plus Water [H2O] giving NH4OH, and the ions from it are NH4+ and OH-).
Hydrogen Bond
This type of bond is formed when the polar (positive) Hydrogen atom in a molecule is attracted to the slightly polar (negative) atom in a molecule. A good example of this is water, H2O. Two Hydrogen atoms each share an electron with Oxygen, which needs two electrons to complete the outer shell. Since the Hydrogen is slightly positive, because it gets a smaller share of the electrons, it is attracted to the slightly negative side of the Oxygen atom, even though it is part of a different molecule.
Summary of Chemical Bond Types
There are two main types of chemical bond, ionic and covalent. They can all be considered to be a sharing of electrons for the purpose of giving each atom an outer electron shell that is complete. The amount of electron sharing is what defines the type of bond.
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