1. Unit 1 Sec 2
Ions

3. 1 shell e
2 shell e
3 shell e

4. Octet Rule
Noble gases, such as neon and argon, are nonreactive in chemical reactions.
-- That is, they are stable
In 1916, chemist Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules.
He called his explanation the octet rule.

5. Octet Rule
The octet rule states that in forming compounds, atoms tend to achieve the electron configuration of a noble gas.

6. Octet Rule An octet is 8 valence electrons.
is associated with the stability of the noble gases.
He is stable with 2 valence electrons (duet).
valence electrons He
Ne 2,
Ar 2, 8,
Kr 2, 8, 14,

7. 1 shell e
2 shell e
3 shell e
protons
neutrons
electrons

8. Na+ 1 shell ---- 2 e 2 shell ---- 8 e protons --- 11 neutrons --- 11
electrons
Na+

9. IONS are atoms or groups of atoms with a positive or negative charge.
An ion forms when an atom or group of atoms loses or gains electrons.
IONS are atoms or groups of atoms with a positive or negative charge.

10. Cation
If a neutral atom loses one or more electrons it becomes a cation.
A cation has lost an electron(s) and therefore has a positive charge
ex. Mg2+
Mg - 2e-  Mg2+

11. Formation of a Sodium Ion, Na+
Sodium achieves an octet by losing its one valence
electron.
2, 8, 1
2, 8
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12. Charge of Sodium Ion, Na+
With the loss of its valence electron,
the sodium ion has a +1 charge.
Sodium atom Sodium ion
11p p+
11e e-
2, 8
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13. Formation of Mg2+
Magnesium achieves an octet by losing its two valence electrons.
2, 8, 2
2, 8
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14. Charge of Magnesium Ion Mg2+
With the loss of two valence
Electrons, magnesium forms a
positive ion with a +2 charge.
Mg atom Mg2+ ion
12p+ 12p+
12e e-
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15. Learning Check A. The number of valence electrons in aluminum is
1) 1e ) 2e-. 3) 3e-.
B. The change in electrons for octet requires a
1) loss of 3e ) gain of 3e ) a gain of 5e-.
C. The ionic charge of aluminum is
1) ) ) 3+.
D. The symbol for the aluminum ion is
1) Al3+. 2) Al3-. 3) Al+.

16. Solution A. The number of valence electrons in aluminum is 3) 3 e-.
B. The change in electrons for octet requires a
1) loss of 3e-.
C. The ionic charge of aluminum is
3) 3+.
D. The symbol for the aluminum ion is
1) Al3+.

17. Formation of Negative Ions
If a neutral atom gains one or more electrons it becomes an anion.
An anion has gained an electron(s) and therefore has a negative charge.
ex. N3-
N + 3e-  N3-

18. Formation of a Chloride, Cl-
Chlorine achieves an octet by adding an electron to its valence electrons.
2, 8, 7
2, 8, 8
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19. Charge of a Chloride Ion, Cl-
By gaining one electron, the chloride ion has a -1 charge.
Chlorine atom Chloride ion
17p p+
17e e- –
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20. Ionic Charge from Group Numbers
The charge of a positive ion is equal to its Group number.
Group 1A(1) = 1+
Group 2A(2) = 2+
Group 3A(3) = 3+
The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number.
Group 6A(16) = = 2-
or = 2-

21. Some Ionic Charges I- Copyright © 2005 by Pearson Education, Inc.
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22. To tell the difference between an atom and an ion, look to see if there is a charge in the superscript!

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

24. Learning Check A. The number of valence electrons in sulfur is
1) 4e ) 6e ) 8e-.
B. The change in electrons for octet requires a
1) loss of 2e ) gain of 2e-. 3) a gain of 4e-.
C. The ionic charge of sulfur is
1) ) ) 4-.

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

26. Solution A. The number of valence electrons in sulfur is 2) 6e-.
B. The change in electrons for octet requires a
2) gain of 2e-.
C. The ionic charge of sulfur is
2) 2-.

27. Ionic and Covalent Bonds:
Atoms form octets
to become more stable.
by losing, gaining, or sharing valence electrons.
by forming ionic bonds or covalent bonds.
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28. Bonds
Forces that hold groups of atoms  
  together and make them function
  as a unit.
Ionic bonds – transfer of electrons
Covalent bonds – sharing of electrons

29. Metals Form Positive Ions
by a loss of their valence electrons.
with the electron configuration of the nearest noble gas.
that have fewer electrons than protons.
Group 1A metals  ion 1+
Group 2A metals  ion 2+
Group 3A metals  ion 3+
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