Simple molecules and covalent bonds
Covalent bonds
- A covalent bond forms when two atoms share a pair of electrons.
- By sharing, each atom gets a full outer shell.
- Covalent bonds form between non-metal atoms.
- Examples: $\text{H}_2$, $\text{HCl}$, $\text{H}_2\text{O}$, $\text{NH}_3$, $\text{CH}_4$ (single bonds); $\text{O}_2$, $\text{CO}_2$ (double); $\text{N}_2$ (triple).
Practice
A covalent bond is:
Covalent bonding is the sharing of electron pairs between non-metal atoms so each gets a full outer shell.
Properties of simple molecules
- Low melting and boiling points: the bonds inside each molecule are strong, but the intermolecular forces between molecules are weak, so little energy separates them.
- Poor conductors: molecules have no overall charge and no free electrons or ions.
Practice
Simple molecular substances have low melting points because:
The intermolecular forces are weak (little energy to separate molecules), even though the bonds inside are strong.
Practice
Simple molecular substances are poor conductors of electricity.
They have no overall charge and no free electrons or ions, so they cannot carry charge.
You've got it
Key idea
- a covalent bond = a shared pair of electrons, between non-metals
- simple molecules have low melting/boiling points — weak intermolecular forces (the bonds inside are strong)
- they don't conduct — no charged particles free to move