1. 5.5 Atoms and Ions

2. ATOMS
An ATOM is an electrically neutral particle with an equal number of positive or negative charges.

3. IONS are atoms or groups of atoms with a positive or negative charge.

4. When an atom or molecule gains or loses an electron it becomes an ion.
A cation has lost an electron(s) and therefore has a positive charge
ex. Mg2+
Mg + energy  Mg2+ + 2e-

5. N + 3e-  N3- + energy An anion has gained an electron(s)
and therefore has a negative charge
ex. N3-
N + 3e-  N3- + energy

6. To tell the difference between an atom and an ion, look to see if there is a charge in the superscript!

7. Which are the ions? anions? cations? elements?
Na+ I- Ca+2 O-2
Na I Ca O
Which are the ions? anions? cations? elements?

8. Why would an element lose or gain an electron?

9. GET STABLE! BE AN OCTET!
Ions will have the same electron configuration of the nearest noble gas.

10. PREDICTING ION CHARGESMg
What is the closest noble gas?

11. Does Mg need to lose or gain electron(s) to achieve the electronic configuration of neon?

12. Prediction: Mg2+

13. PREDICTING ION CHARGESF
What is the closest noble gas?

14. Does F need to lose or gain electron(s) to achieve the electronic configuration of neon?

15. Prediction: F-

16. Charges on Common Ions 3- 2- 1- 1+ 2+
By losing or gaining e-, an ion will have the same number of e-’s as nearest Group 18 atom.

17. Charges on Common Ions 3- 2- 1- 1+ 2+
Another way to think about this: look at the group number!

18. nonmetals (F) gain electrons ---> anions (F-)
In general
metals (Mg) lose electrons ---> cations (Mg2+)
nonmetals (F) gain electrons ---> anions (F-)

19. How would you write the symbol for the sodium ION?
How many valence electrons does sodium have?

20. Learning Check – Counting
State the number of protons, neutrons, and electrons in each of these ions.
39 K O Ca 2+
#p+ ______ ______ _______
#no ______ ______ _______
#e- ______ ______ _______

21. Remember an electron is negatively charged
Remember an electron is negatively charged. When you lose them an atom becomes a positively charged ion…

22. When an atom gains electrons it becomes a ___________ charged ion