1. Ch. 7 Ionic Bonding
Chemistry

2. Review
1. What is an ion?
ion – an atom with a positive or negative charge (an electron has been lost or gained)
2. Where on the periodic table are the metals located? Nonmetals?

3. Valence Electrons
Core Electrons – “inner” electrons, do not participate in bonding
Valence Electrons – “outer” electrons, electrons in the highest occupied energy level
number of valence electrons largely determines the chemical properties of an element
So which electrons in an electron configuration are core and valence?
Be – [He] 2s2 P – [Ne] 3s2 3p3
Core Valence Core Valence

4. So how do I find this valence number?
The valence electrons an atom has is the same as its group number for a representative (main group) element

5. How do I keep track of all these valence electrons?
What do you notice about valence electrons down a group?
Electron configuration remains the same down a group, only the core electrons change

6. Octet Rule All elements want eight valence electrons (except H and He)
Why?
Achieve noble gas configuration, most STABLE
2 electrons come from the s subshell and 6 from the p subshell
Why can H and He NOT have eight valence electrons (Hint: they are considered stable with TWO valence electrons)
No p subshell!

7. Octet Rule
Elements will tend to gain or lose enough electrons to fulfill their octet
Will metallic elements gain or lose electrons?
Lose, much easier to lose electrons than gain electrons
Will nonmetallic elements gains or lose electrons?
Gain, much easier to gain electrons (can also share electrons)

8. Octet Rule Metallic elements lose electrons
Why?
In simple terms…easier to lose than to gain to form the octet
Nonmetallic elements gain electrons
In simple terms, easier to gain a few electrons than lose them
Now let’s consider periodic trends!
Nuclear attraction across:
Shielding effect across:
Kinetic energy across:
This means:
Increases across, nonmetals held tighter than metals
Remains constant, does not offset nuclear attraction
Remains constant
Metals hold onto their electrons less tightly so it is easier for metals to lose their electrons. Additionally, nonmetals hold onto their electrons tighter . This trend, and the fact that nonmetals have higher electron affinity, means nonmetals tend to gain electrons.

9. Octet Rule
If metals lose electrons, they will form ions. Will these ions be negatively or positively charged?
If nonmetals gain electrons, will their ions be negatively or positively charged?

10. Ionic Bonding
Ionic compound – composed of metal cations and nonmetal anions
They are still electrically neutral
Why?
The charges of the cation and anion cancel out
The negatively charged anion and the positively charged cation attract each other by electrostatic forces (force holding a cation and anion together due to their charge)

11. Ionic Bonding
We can use Lewis structures to show how ionic compounds form
Ex: 4 Li + O2  2 Li2O
Breaking this to Lewis structures:
1s2 2s s2 2s2 2p4  [He] [Ne]
The ions now obey the octet rule and are happy!

12. Another Example Ex: 3Mg + N2  Mg3N2
Breaking this into Lewis structures:
[Ne] 3s s2 2s2 2p [Ne] [Ne]