1. Chemical Bonding I Basic Concept
Chapter Nine
Chemical Bonding I
Basic Concept

2. Chapter Nine / Chemical bonding I, Basic Concept
Valence Electrons
Valence electrons: are the outer shell electrons of an atom. The valence electrons are the electrons that participate in chemical bonding.
Group
# of valence e-
e- configuration 1A 1
ns1 2A 2
ns2 3A 3
ns2np1 4A 4
ns2np2 5A 5
ns2np3 6A 6
ns2np4 7A 7
ns2np5

3. Chapter Nine / Chemical bonding I, Basic Concept
Lewis Dot Symbols
Lawis dot symbol consists of the symbol of an element and one dot for each valence electron in an atom of the element.
The octet rule: in forming chemical bonds, atoms usually gain, lose or share electrons until they have 8 in the outer shell to reach the same electronic configuration of the noble gasses (ns2 np6).
There are two main types of chemical bonds: ionic bond and covalent bond.

4. Chapter Nine / Chemical bonding I, Basic Concept
Lewis Dot Symbols
Lewis dot symbol for representative elements and noble gases

5. Chapter Nine / Chemical bonding I, Basic Concept
Ionic Bond
There are two type of bonds: Ionic bond and covalent bond.
An ionic bond is the electrostatic force that holds ions together in an ionic compound.
Ionic bond occurs normally between metal and nonmetal and the electron transfer from element to another element.
Example: -
Li + F Li F
1S2 2S S22S22P S S22S22P6

6. Chapter Nine / Chemical bonding I, Basic Concept
Ionic Bond
Example 2
Use Lewis dot symbol to show formation
of Al2O3
2 Al
3 O →
[Ne] 3s2 3p1
1s2 2s2 2p4
(Al2O3)
2 Al
3 O -2
[Ne]
1s2 2s2 2p6 [Ne]

7. Chapter Nine / Chemical bonding I, Basic Concept
Ionic Bond
Example:
An atom in the ground state has atomic number Z=5. Choose the correct electron-dot structure which represents this atom?
a. X
The electron configuration Z =5
1s2 2s2 2p1
Valence electrons are in 2s2 2p1
VE = 3 e
b. X
c. X
d. X

8. Chapter Nine / Chemical bonding I, Basic Concept
Covalent Bond
Covalent bond, is a bond in which two electrons are shared by two atoms.
Covalent bond occurs normally between nonmetal and nonmetal and the electron only shared between elements (not transfer from element to another element).
Example:
F F
8e-
8e- F
7e-
7e-
single covalent bond F F
single covalent bond

9. Chapter Nine / Chemical bonding I, Basic Concept
Covalent Bond
lone pairs: pairs of valence electrons that are not involved in covalent bond formation.
A Lewis structure is a representation of covalent bonding in which shared electron pairs are shown either as lines or as pairs of dots between two atoms, and lone pairs are shown as pairs of dots on individual atoms.
lone pairs F
single covalent bond
single covalent bond F

10. Chapter Nine / Chemical bonding I, Basic Concept
Covalent Bond
Lewis structure of water
single covalent bonds O
2e-
8e-
2e- H + + H O H or
Double bond – two atoms share two pairs of electrons
8e-
8e-
8e-
double bonds O C or O C
double bonds
Triple bond – two atoms share three pairs of electrons
triple bond
8e- N
8e- or N
triple bond

11. Bond length is defined as the distance between the nuclei
Chapter Nine / Chemical bonding I, Basic Concept
Valence Electrons
Bond length is defined as the distance between the nuclei
of two covalently bonded atoms in a molecule
Bond Lengths
Triple bond < Double Bond < Single Bond

12. Chapter Nine / Chemical bonding I, Basic Concept
Electronegativity
Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms H F
electron rich
region
electron poor
region
e- poor
e- rich F H d+ d-

13. Electron Affinity - measurable, Cl is highest
Chapter Nine / Chemical bonding I, Basic Concept
Electronegativity
Electronegativity : the ability of an atom to attract toward itself the electrons in a chemical bond.
Elements with high electronegativity have a greater tendency to attract electrons than do elements with low electronegativity.
Electron Affinity - measurable, Cl is highest
X (g) + e X-(g)
Electronegativity - relative, F is highest

14. Chapter Nine / Chemical bonding I, Basic Concept
Electronegativity

15. Classification of bonds by difference in electronegativity
Chapter Nine / Chemical bonding I, Basic Concept
Electronegativity
Classification of bonds by difference in electronegativity
Difference
Bond Type
Covalent
 2
Ionic
0 < and <2
Polar Covalent
Increasing difference in electronegativity
Covalent
share e-
Polar Covalent
partial transfer of e-
Ionic
transfer e-

16. Chapter Nine / Chemical bonding I, Basic Concept
Electronegativity
Example
Classify the following bonds as ionic, polar covalent, or covalent
A) HCl
b) KF
c) C-C
3-2.1 =0.9
Polar covalent
4-0.8 =3.2
Ionic =0
covalent

17. Chapter Nine / Chemical bonding I, Basic Concept
Electronegativity
Example
Classify the following bonds as ionic, polar covalent, or covalent
A) CsCl
b) H2S
c) N-N
3 – 1 = 2
Ionic
= 0.4
Polar covalent
3 - 3 = 0
covalent

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