In this article, we look at the types of bonds in chemistry. We explain what is a chemical bond, list the types of chemical bonds, and give chemical bond examples. Bonds are very important in chemistry, as they dictate many of the chemical properties that a compound has.
When atoms are attracted to each other and join together to form a molecule, we call the connection between each atom a chemical bond. The bond “holds together” the atoms in the molecule, ion, or crystal. The bonds can often last indefinitely, until they are broken apart by an external force or energy.
Chemical bonding is the attraction between two or more atoms that allows them to be able to form a stable chemical compound. The specific nature of a chemical bond can vary, but the most commonly known are covalent and ionic bonds. With these bonds, it provides sufficient energy between atoms when one has less. It’s the force of attraction that holds atoms, allowing the electrons to form a bond together.
Primary and Secondary Bonds
The chemical bond can be one of two types; primary and secondary bonds. In the primary bond, there are covalent, ionic, and metallic bonds. In the secondary bonds, there are hydrogen and Van der Waals bonds. These bonds are weaker and longer-range than primary bonds, because they do not involve ions or sharing of electrons.
Chemical Bond Types
What are the types of bonds in chemistry? Let’s look at three of the most popular types of bonds – covalent bonds, ionic bonds, and metallic bonds.
A covalent bond, or molecular bond, is a chemical bond formed between two atoms that share a pair of electrons; the elements that form these bonds are generally non-metals. Some examples of oxygen, hydrogen and nitrogen in compounds like O2 and H2O). A defining characteristic of a covalent bond is that electron density is high in the middle of the bond. This means that electrons are more likely to be found in between the two atoms than at each end. Chemists sometimes describe and predict the ways that covalent bonds form using a model called molecular orbital theory.
Covalent bonds can be either single or multiple bonds. In a single bond, only one pair of valence electrons are being shared between two atoms. However, sometimes atoms share more than one electron pair, forming what is called a multiple bond. The common types of multiple bonds are double and triple, with higher order bonds forming only in certain exotic compounds of transition metals. The elements that most often participate in multiple bonding are: carbon, nitrogen, oxygen, phosphorus, and sulfur.
A covalent chemical bond can be either polar or non-polar. A polar covalent bond shares electrons unequally, which means the distribution is unbalanced and leaves one atom with a partial negative charge and the other with a partial positive charge. A nonpolar covalent bond shares electrons equally across both atoms, resulting in a balanced distribution, and can only truly form between two atoms of the same element. However, sometimes chemists distinguish between “mostly” nonpolar covalent bonds and polar covalent bonds, using the electronegativity difference between the atoms. If the electronegativity difference is less than about 0.4 units, a bond is commonly considered nonpolar. If the difference is more than 0.4, then the bond is polar by this standard. With a difference of more than 1.8 units, the bond is no longer covalent at all, but ionic (see below).
This type of chemical bond involves transfer of electrons from one atom to another, usually from a metal to a non-metal (Examples include NaCl and Li2O).
- An ionic compound has full positive and negative charges since electrons are not shared but “stolen” by the more electronegative atom.
- The atom that loses electrons has a positive charge, while the one that gains electrons has a negative charge.
Metallic bonds are chemical bonds among the atoms in a metal. Similar to a sea of freely moving electrons, these bonds connect all the atoms in the metal at once (in contrast to covalent bonds, in which atoms share discrete pairs of electrons over specific parts of a molecule). These chemical bonds are responsible for many properties of bulk metals, including their luster and electrical and thermal conductivity.
Chemical Bond Topics in Other Articles
- Ionic vs. Covalent Bonds
- What Are Hydrogen Bonds
- Intermolecular Forces
- Ion-dipole Forces Explained
- Bond Formation Energies
The Chemical Bond and the Octet Rule
Atoms have electrons called valence electrons that are furthest from the nucleus and participate in chemical bonds. These electrons must be shared or transferred to achieve the octet rule, which states that atoms must have eight electrons in their outer shell in order to achieve stability. However, this rule only applies to the main group elements such as carbon and nitrogen.
Boron is a notable exception to the octet rule, as it often prefers to have only 6 electrons, forming compounds like BF3 or boric acid (H3BO3). Elements in the third row of the periodic table and beyond can have an expanded octet, which means they have more than eight electrons in their valence shells. Phosphorus, sulfur and iodine are common elements that can have an expanded octet.