Single Covalent Bonds
A single covalent bond is formed when only one pair of electrons is shared between atoms. A sigma bond is the strongest type of covalent bond, in which the atomic orbitals directly overlap between the nuclei of two atoms.
Covalent compounds
Covalent compounds are formed when electrons are shared between atoms.
Only non-metal elements participate in covalent bonding
As in ionic bonding, each atom gains a full outer shell of electrons
When two or more atoms are chemically bonded together, we describe them as ‘molecules’
Difference between Ionic & Covalent Compounds
| Ionic Compounds | Covalent Compounds |
|---|---|
| 1) Have high melting and boiling points so ionic compounds are usually solid at room temperature, 2) Not volatile so they don’t evaporate easily 3) Usually water-soluble as both ionic compounds and water are polar, 4) Conduct electricity in molten state or in solution as they have ions that can move and carry a charge. | 1) Have low melting and boiling points so covalent compounds are usually liquids or gases at room temperature, 2) Usually volatile which is why many covalent organic compounds have distinct aromas 3) Usually not water-soluble as covalent compounds tend to be nonpolar but can dissolve in organic solvents, 4) Cannot conduct electricity as all electrons are involved in bonding so there are no free electrons or ions to carry the charge. |
Melting & Boiling Points of Ionic & Covalent Compounds
Ionic compounds have high melting and boiling points
This is because the oppositely charged ions in the lattice structure are attracted to each other by strong electrostatic forces which hold them firmly in place
Large amounts of energy are needed to overcome these forces so the m.p. and b.p. are high
Simple covalent substances, such as carbon dioxide and methane, have very strong covalent bonds between the atoms in each molecule, but much weaker intermolecular forces between individual molecules
When one of these substances melts or boils, it is these weak intermolecular forces that break, not the strong covalent bonds
Less energy is needed to break the molecules apart, so they have lower m.p. and b.p. than ionic compounds
