1. Chemical Bonding
Chapter 6

2. Chemical Bonding
Chemical bond —mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.
Why do bonds form?
stability (lower energy) is achieved when compared to the unbonded states.

3. Types of Intramolecular Bonds
ionic bonds (electrical attraction between ions) {Electron Transfer}
metallic bonds (“delocalized” electrons) {Electron Sea}
covalent bonds (sharing of electrons)
All involve electron interactions.
The difference arises in how they interact.

4. Distinguishing between covalent and ionic bonds:
Look at ELECTRONEGATIVITY of the atoms involved.
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The DIFFERENCE in the electronegativities of the bonding atoms will tell you what type of bond is formed.

5. Distinguishing between covalent and ionic bonds cont…
Electronegativity Difference
Type of Bond
0.00 – 0.39
Nonpolar-covalent
0.40 – 1.7
Polar-covalent
1.71 – 4.00
Ionic

6. Hydrochloric Acid

7. Distinguishing between covalent and ionic bonds cont…
Polar bonds —arise when electron density (orbitals) are NOT evenly distributed (electrons are held closer to atom with the LARGER electronegativity)
partially positive
partially negative

8. Distinguishing between covalent and ionic bonds cont…
Nonpolar bonds —arise when atoms have similar electronegativities (electrons evenly distributed between atoms)
Nonpolar Bond Cl Cl
Electronegativity Difference
= 0
Polar Bond
Electronegativity Difference
l l = 0.9 H Cl

9. Octet Rule
Compounds tend to form so that each atom has eight valence electrons (noble gas configuration)
gain, lose, or share electrons

10. Octet Rule Exceptions:
H, Be, B, and some nonmetallic elements in 3rd period in these elements’ families
Hydrogen needs 2 valence electrons total
Beryllium needs 4 valence electrons total
Boron needs 6 valence electrons total

11. Octet Rule Cont…
Some need more than 8 valence electrons and are known as expanded octets because they are not full until they have 10 e- or even 12 e-
Elements that are expanded octet can be satisfied with only 8 e- in certain molecules.
most common: Sulfur (12) may do this
Phosphorus (10) may do this
Halogens (10 & 12) may do this
Noble gases (10 & 12) may do this

12. Electron-dot (Lewis) Structures Cont…
We Use Electron Dot diagrams for elements by telling the number of valence electrons
Draw the Dot Diagram for Elements
Nitrogen Hydrogen N H
Bonding Site
Bonding Site
Bonding Site
Nitrogen needs 3 electrons to be full
Hydrogen only needs 2 electrons to be full, so it needs 1 more

13. Electron-dot (Lewis) Structures
We only use Electron Dot Diagrams for covalent compounds , ions or single elements.
Rules for Drawing
Uncombined Elements:
show VALENCE electrons (use periodic table) and do NOT need to follow the octet rule
Monatomic Ions:
Use Straight line brackets with the charge outside.
Cations = lose electrons
Anions = gain electrons
Covalent Compounds & Polyatomic Ions:
Use the following slides of information
and follow all steps exactly.
Follow Octet Rule

14. Lewis Dots for Elements
= one valence electron v
Symbol of Element 1 5 8 X 2
You must place one
Electron (dot) into each position, before you pair.
(Top,Right,Bottom,Left) 4 6 7 3

15. Cations -vs- Anions
CATIONS
Example: K+1
ANIONS
Example: O -2

16. Electron-dot (Lewis) Structures Cont…
When bonding:
H is never central atom (O is rarely)
The number of electrons EACH atom needs to complete its octet is the number it needs to SHARE with other atoms
2 shared electrons (1 pair) = 1 bond
Bonds are indicated with a
Unshared electrons do NOT go between atoms
NOT counting the shared electrons, each atom should still have its correct number of valence electrons*

17. Electron-dot (Lewis) Structures Cont…
Multiple Bonds
Double bond e- shared O2
Triple bond  e- shared N2
Quadruple bond  e- shared C2

18. Step 1: Count the number of valence electrons.
Steps to Follow…
Step 1: Count the number of valence electrons.
Step 2: Draw a structure with single bonds joining the atoms to the central atom.
Central atoms are the atom that can make the most bonds usually (or they are the single atom in the compound).

19. Steps to Follow…
Step 3: Place lone pairs (unshared pairs) around each element to make them follow the octet rule. (Don’t forget the exceptions.)
Step 4: Count the electrons in the newly made structure.
If they match it is probably the correct structure…so use it.

20. Steps to Follow…
If there are TOO MANY electrons around the new structure, take off 2 sets of lone pairs (one off each atom) and make a double bond or more until the totals match.
If there are NOT ENOUGH electrons then add lone pairs to the central atom until the totals match.

21. Polyatomic Ions: put entire structure in a [ ]
charge is superscript outside brackets

22. Resonance Structure
Some molecules and ions need to be represented by more than one Lewis structure.
Ex. O3
Actual structure: average of all structures used to represent resonance structures
NOTE: substances with odd number of valence electrons are stable because multiple resonance structures can be drawn to show different bonding configurations.

23. Resonance Structure Cont…
When can you usually draw resonance structures?
at least one double bond present, along with single bonds between similar atoms

24. Electron-dot (Lewis) Structures Cont…
Occasionally, one atom must contribute BOTH electrons to make a bond
coordinate covalent bonds
IDENTICAL to regular covalent bonds
Indicated with an