1. Lewis Symbols
To help us to focus on the valence electrons – those that can participate in bonding - we use Lewis Symbols (in honor of scientist G.N. Lewis)

2. Lewis Dot Symbols Lewis Dot symbol (or Electron dot symbol)
Dots placed around an element’s symbol represent valence electrons
Pair electrons as needed
Ions are placed in brackets with charge outside
Easily shows “Octet rule”
Tendency of an atom to achieve an electron configuration having 8 valence electrons
Same as the electron configuration of a noble gas
The 8 electrons shown as 4 pairs

3. Group Practice:
Write out dot diagrams showing the valence electrons of the following atoms. Use principles of electron configuration to predict and explain the ionic compounds each pair will react to form:
Magnesium fluoride
Aluminum oxide
Nickel(II) chloride

4. Molecular Compounds Write the orbital diagram for a hydrogen atom.
We have seen evidence from gaseous reactions that elemental hydrogen exists as a diatomic molecule. Use your orbital diagram to explain why hydrogen atoms would be more stable (lower chemical energy) as H2 molecules.

5. Electron Dot Diagrams for the Diatomic Elements
How does hydrogen obtain a noble-gas electron configuration?

6. Covalent Compounds and Bonding
When two nonmetals form a compound, the bond between atoms is covalent.
Both atoms are close to the noble-gas electron configuration, so sharing electrons will allow both to obtain it.
In a covalent bond, each shared electron is attracted simultaneously to two nuclei.

7. Covalent Bonds Electrons not transferred in this case
Electrons typically shared in pairs

8. Carbon Dioxide Example
The atoms of CO2 molecules are held together by strong covalent bonds.
No bonds connect the molecules, so CO2 molecules separate easily from each other into the gas state at room temperature.
Figure 8.13
Figure from p. 28

9. Whiteboard Practice HF CF4 O2 CO2
Use valence electron concepts and electron dot diagrams to represent these compounds: HF
CF4 O2
CO2

10. The Octet Rule
Just as in ionic bonding, covalent bonds are formed so that each atom can have the noble-gas electron configuration. Noble gases have 8 valence electrons, an octet.

11. The Halogens Do the atoms in each of these molecules have an octet?
Why do the halogens exist as diatomic molecules?

12. Multiple Bonds How many valence electrons does an oxygen atom have?
How many does it need to obtain an octet?
O2 has a double bond, two pairs of shared electrons
How many valence electrons does a nitrogen atom have?
N2 has a triple bond, three pairs of shared electrons

13. The Octet Same as the electron configuration of a noble gas
An unreactive or stable compound usually has the maximum number of valence electrons per core (8)
Same as the electron configuration of a noble gas
Covalently bonded atoms achieve 8 valence electrons by sharing electrons
The 8 electrons exist in 4 pairs
H atoms bond with other atoms to obtain a total of 2 electrons like He (duet).

14. Practice: Valence Electrons and Number of Bonds
How many bonds do each of the following atoms tend to form? H Cl O N C

15. Carbon Compounds Carbon has:
Figure 8.21
Carbon has:
Four valence electrons
The ability to form four bonds
The ability to bond to itself
Very strong bonds when bonded to itself
Carbon molecules are ubiquitous in nature.
Aside from what I’ve mentioned here, skip “Bonding in Carbon Compounds”, pp (top).

16. Hydrocarbons Aromatic hydrocarbons
A class of hydrocarbons which has carbon atoms arranged in a six-atom ring with alternating single and double bonds
Delocalized structures
Figure 8.22
Figure 8.22

17. Functional Groups in Hydrocarbons

18. Ionic and Covalent
In ionic compounds, ions are held together by electrostatic forces – forces between oppositely charged ions.
In molecular compounds, atoms are held together by covalent bonds in which electrons are shared.
Figure 8.2

19. Activity: Identifying Types of Bonding
Identify the type of bonding in each of the following substances:
NaF
ClO2
FeSO4
SO2
Ca(ClO2)2

20. Steps for Writing Lewis Structures
Write an atomic skeleton.
Sum the valence electrons from each atom to get the total number of valence electrons.
Place two electrons, a single bond, between each pair of bonded atoms (can also be drawn as a line)
Place remaining valence electrons to complete the octet of each outer atom. These are called non-bonding electrons or lone pairs. If there are “extra” electrons, place the pairs around the central atom.
If necessary to satisfy the octet rule, shift unshared electrons from non-bonded positions on atoms with completed octets to positions between atoms to make double or triple bonds.

21. Activity: Lewis Structures
Draw Lewis structures to show how electrons are shared in these molecules.
C2H6
C2H4
C2H2
HCN
CO2
NH3