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                                                                                                                                                      Last updated:  03/08/2010


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Covalent vs. Ionic Bonding

                                 FACTS
1.  Atoms can attain a more stable arrangement of electrons in their outermost shell by interacting with one another.

2.  An ionic bond is formed when electrons are transferred from one atom to the other.

3.  A covalent bond is formed when electrons are shared between atoms.

4. The two cases shown represent extremes.  Often, covalent bonds form with a partial transfer (unequal sharing of electrons), resulting in a polar covalent bond

                             Atomic Bonding

                                                  IONS

Formation of Ions

Normal Configurations: Sodium: 11 p+, e-; Chlorine: 17 p+, e-

You may have heard that the pictures above are not really accurate. If you want to know more, you can visit

                               ELECTRON SHELL STRUCTURE
                   Most stable arrangement: 8 e- in outermost shell

bulletNoble gases (Ar, Ne, etc.) have that arrangement naturally and rarely combine with anything else.
bulletSodium: Loses electron, has 11p+, 10e-, charge +1: becomes a cation
bulletChlorine: Gains electron, has 17p+, 18e-, charge -1: becomes an anion
bulletMany elements would have to gain or lose too many electrons and settle for other electron structures instead.
bullet(+) and (-) Cancel Out

                              Ionic and Covalent Bonding

Ionic and Covalent Bonding

bulletIonic Bonding
bulletSome atoms gain electrons to become anions
bulletOthers lose electrons to become cations
bulletIons are attracted by their opposing charges
bulletElectrical Neutrality Maintained
bulletMost Important Bonding in Rocks and Minerals
bulletCovalent Bonding
bulletElectrons share electrons to fill incomplete shells
bulletMost Important Bonding in Organic Materials (and Organisms)

 

                      LATTICE Crystals in Ionic Bonding

Usually anions are bigger (They form framework and cations fill in spaces between). Thus it is often possible to remove one cation and replace it with another. Below, both halite (NaCl) and sylvite (KCl) have identical atomic structures and similar physical properties. They can be distinguished by their taste - sylvite is very bitter, somewhat like licking a belt sander. Those of you who have used so-called "light salt" know (salt substitute).
lattice