1 The molecule

• A water molecule (H₂O) is formed by binding one oxygen atom to two hydrogen atoms.
• Each hydrogen atom is joined to the oxygen atom by a single covalent bond.

• A covalent bond is a chemical bond between two atoms in which each atom shares one or more electrons with the other.
• In a water molecule, oxygen (six outer electrons) needs two more electrons to complete its outer shell of eight; each hydrogen (one electron) needs one more to complete its shell of two.
• By sharing, oxygen forms two covalent bonds and each hydrogen forms one:

        O
      /   \          H–O–H   angle ≈ 104.5°
     H     H