Types of Chemical Bonds Explained
In chemistry, atoms are held together by chemical bonds. The type of bond formed dictates many of the substance’s properties. Three primary types of chemical bonds are covalent, metallic, and ionic.
Covalent Bonds
In a covalent bond, two bonded atoms share electrons. When the atoms joined by a covalent bond are the same (e.g., N₂, O₂), neither atom attracts the shared electrons more strongly than the other. This is called a nonpolar covalent bond or simply nonpolar.
If the atoms of the covalent bond are different elements (e.g., NO), one tends to attract the shared electrons more strongly. The electrons spend more time near that atom, and this bond is called a polar covalent bond. Polar covalent molecules have a positive and a negative electric pole due to the unequal sharing of electrons.
Covalent substances generally do not conduct electricity and have no metallic brightness, ductility, or malleability.
Types of Covalent Bonds
- Single bond: Atoms share one pair of electrons.
- Double bond: Atoms share two pairs of electrons.
- Triple bond: Atoms share three pairs of electrons.
- Coordinate covalent bond: A type of covalent bond where one atom provides both shared electrons. It is represented by an arrow (→) starting from the donor atom to the acceptor atom.
Metallic Bonds
A metallic bond is a chemical bond that holds metal atoms together. It is essentially the attraction between metal cations and a “sea” of delocalized valence electrons. These atoms are grouped very close to each other, resulting in very compact structures.
Metals typically form three-dimensional networks, often acquiring a close-packed structure where each metal atom is surrounded by twelve other atoms (six in the same plane, three above, and three below).
Because metals have low electronegativity, their valence electrons are delocalized and can move freely throughout the metal structure. This electron mobility gives metals their characteristic electrical and thermal properties.
Properties of Metals
- Usually solid at room temperature (except mercury); melting and boiling points vary greatly.
- High thermal and electrical conductivity (due to mobile valence electrons).
- Metallic shine.
- Ductile and malleable (mobile valence electrons allow metal cations to move without breaking the structure).
- Can emit electrons when heated (thermionic emission).
- Exhibit the photoelectric effect (emit electrons when exposed to light).
Ionic Bonds
In chemistry, an ionic bond is the chemical bond resulting from the electrostatic attraction between oppositely charged ions. It occurs when one atom transfers one or more electrons to another.
Typically, a metal atom donates one or more electrons to form a cation (a positively charged ion) with a stable electron configuration. These electrons are accepted by a nonmetal atom, forming an anion (a negatively charged ion) which also achieves a stable electron configuration. The strong electrostatic attraction between these oppositely charged ions causes them to unite and form an ionic bond.
Ionic compounds form crystal lattices composed of oppositely charged ions held together by strong electrostatic forces. This strong attraction determines their observed properties.
Properties of Ionic Compounds
- Solid crystalline structure (often cubic).
- Formed by electron transfer from a metal to a nonmetal.
- High melting and boiling points.
- Typically formed between Group 1 or 2 metals and Group 16 or 17 nonmetals.
- Soluble in polar solvents (solubility varies).
- Conduct electricity when molten or dissolved in water.
- Do not conduct electricity in the solid state.