1. Ions

2. Atoms are neutral. BUT when an atom gains or loses an electron it becomes an ion. Ions can be positive or negative.

3. Cations Positive ions are called cations – A cation is formed when an atom loses electrons

4. Cation Example #1 – Lithium (Li) The lithium atom has 3 electrons total, 2 in the first energy level and 1 in the second energy level. The lithium ion has 2 electrons total and a positive charge of 1+. One electron has been lost. When an electron is lost an atom becomes a positive ion or a cation.

5. Cation Example #2 – Sodium (Na) The sodium atom has 11 electrons total, 2 in the first energy level, 8 in the second energy level, and 1 in the third energy level. The sodium ion has 10 electrons total and a positive charge of 1+. One electron has been lost. So the charge is 1+.

6. Cation Example #3 – Magnesium (Mg) The magnesium atom has 12 electrons total, 2 in the first energy level, 8 in the second energy level, and 2 in the third energy level. The lithium ion has 10 electrons total and a positive charge of 2+. Two electrons have been lost. So the charge is 2+.

7. Cation joke… “I think I’ve lost an electron…” “Are you sure?” “I’m positive!”

8. Anions Negative ions are called anions – An anion is formed when an atom gains electrons

9. Anion Example #1 – Fluorine (F) The fluorine atom has 9 electrons total, 2 in the first energy level and 7 in the second energy level. The fluorine ion has 8 electrons total and a negative charge of 1-. One electron has been gained. When an electron is gained an atom becomes a negative ion or an anion.

10. Anion Example #2 – Chlorine (Cl) The chlorine atom has 17 electrons total, 2 in the first energy level, 8 in the second energy level, and 7 in the third energy level. The chlorine ion has 18 electrons total and a negative charge of 1-. One electron has been gained. So the charge is 1-.

11. Anion Example #3 – Oxygen (O) The oxygen atom has 8 electrons total, 2 in the first energy level and 6 in the second energy level. The oxygen or (oxide) ion has 10 electrons total and a negative charge of 2-. Two electrons have been gained. So the charge is 2-.

12. Ion Charges & the Periodic Table 1+nc 2+ 3+2-1- Li + Be 2+ O 2- F-F- Na + Mg 2+ Al 3+ S 2- Cl - K + Ca 2+ Ga 3+ Se 2- Br - Rb + Sr 2+ In 3+ Te 2- I-I- Cs + Ba 2+ These elements have an assigned charge based on their periodic column (or group). Hydrogen is an exception.