Chemical Bonds

All matter is made up of atoms.

Atoms consist of a nucleus of positively charged protons and neutral neutrons. Negatively charged electrons orbit the nucleus. Two or more atoms bonded together form a molecule. The arrangement of electrons determines what kind of chemical bonds the atom makes.

• In an ionic bond one or more of the orbiting electrons is transferred from one atom to the other. Since the addition or subtraction of the electrons changes the overall charge of the atom, it is now referred to as an ion. The atom that received the electrons becomes a negative ion or an anion. The atom that lost the electrons becomes a positive ion or cation. The bond between a cation and an anion is an ionic bond. An example of an ionic bond is the bond formed in a molecule of sodium chloride (NaCl).
  
  
• In a covalent bond orbiting electrons are shared between atoms. There are two types of covalent bonds. If the electrons are shared equally between the two atoms, then the bond is nonpolar covalent. If one of the two atoms tends to pull the shared electrons towards it more than the other atom, then the bond is polar covalent.
  
  
• While both ionic and covalent bonds are intramolecular (that is they occur within the molecule itself), hydrogen bonds are intermolecular (that is they occur between molecules). Hydrogen bonds form between the positive end of a polar covalently bonded molecule and the negative end of another polar covalently bonded molecule. They are the weakest of all the bonds discussed so far. An example of a hydrogen bond is the bond that occurs between two water molecules.