Covalent bonds.

  1. Hydrogen (H2): two hydrogen atoms can form a single covalent bond by sharing one pair of electrons.

  2. Oxygen (O2): two oxygen atoms share two pairs of electrons to form a double covalent bond.

  3. Water (H2O): two hydrogen atoms and one oxygen atom are joined by single covalent bonds to produce a molecule of water.

  4. Methane (CH4): four hydrogen atoms can satisfy the valence of one carbon atom, forming methane.