1. Ion Formation

2. Neutral atoms have equal numbers of protons and electrons.

3. BUT…atoms can gain or lose electrons forming charged particles called ions.

4. An atom that loses an electron will have more positive charges than negative charges. • The ion will be positively charged. (cation)

5. An atom that gains an electron will have more negative charges than positive charges. • The ion will be negatively charged. (anion)

6. Why do atoms form ions? To complete their outer energy levels. • 1st energy level is complete with 2 electrons. • All other energy levels are complete with 8 electrons. (stable octet)

7. Electrons in the outer energy levels have a special name. • Electrons in the outer energy level of an atom are called valence electrons.

8. You can predict the type of ion that an atom will form. It depends on the number of valence electrons the atom has. Atoms with less than 4 valence electrons lose all of their valence electrons more than 4 valence electrons gain the number needed to get to 8

9. The periodic table can be used to determine the number of valence electrons in an atom of any element. • Elements in the same group have the same number of valence electrons.

10. If you know the number of valence electrons you can determine how the atom will become an ion. REMEMBER: • Less than 4 valence electrons – lose all • More than 4 valence electrons – gain to 8

11. Ions have a charge and the symbol of the ion can be written as follows: Mg2+ The charge on the ion is written as a superscript.