Covalent Bonding

• In covalent bonding, electrons are  shared between atoms
• Covalent bonds form between non metallic atoms. 
• In a water molecule, the hydrogen and oxygen atoms are held together by covalent bonds. 

  Before bonding, each hydrogen atom requires 1 extra electron to complete its outer shell, and so wants to form 1 covalent bond. Meanwhile, each oxygen atom requires 2 more electrons, and so wants to form 2 covalent bonds. 

  This means that water molecules will be made from 2 hydrogen atoms and 1 oxygen atom, so that all the atoms obtain full outer shells.