1. Covalent Bonding
Lesson Two

2. Chemical Bonding Two ways: 1. Sharing electrons between two atoms
Both atoms are close to having full levels
Electrons are shared back and forth between two atoms to
make both feel satisfied
2. Transferring electrons between two atoms
One atom is close to having a full level, while the other is close to emptying a level
Electrons are transferred from the almost empty atom to the almost full atom to make both satisfied

3. Review
Electronegativity: a measure of an atom’s tendency to pull a bonding electron toward itself
The closer two atoms’ electronegativity values are to each other, the more they share
The cut-off value is considered to be 1.7:
Electronegativity difference < 1.7 implies sharing
Electronegativity difference > 1.7 implies transfer

4. Molecules A molecule is a group of atoms joined by covalent bonds
Here is a visual to show the sharing of electrons in a covalent bonded water molecule:
Water

5. Polar Covalent Electronegativity - 0.5 and 1.7
Covalent bonds in which the sharing of the electron pair is unequal
The more electronegative atom has the greater electron density
Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms

6. Polar Covalent
In such a bond there is a charge separation with one atom being slightly more positive and the other more negative,
the bond will produce a dipole moment.
The ability of an atom to attract electrons in the presence of another atom is a measurable property called electronegativity.

7. Non Polar Covalent Electronegativity – 0.5 or less
In this covalent bond, the atoms share the electrons equally
There is no dipole moment
An example of this is a Fluorine molecule
Carbon – Hydrogen bond is also non polar covalent
Think of three other combinations

8. Octet Rule
Only noble gases are allowed to exist independently in nature
They can do this because of the stability of their electron configuration
Let’s understand why
What is the electron configuration for Ar and Xe?

9. Octet Rule
As you can see, the stability results from the fact that all of the orbitals are completely filled
Other atoms can have this stability by filling their outermost s and p orbitals with electrons by sharing electrons through covalent bonding
Octet rule: chemical compounds tend to form so that each atom, by gaining or losing or sharing electrons, has an octet of electrons in its highest occupied energy level

10. Octet Rule
Electrons are either shared by single, double, or triple bonds
A single bond is a covalent bond produced by the sharing on one pair of electrons between two atoms
A double bond is a covalent bond produced by the sharing of two pairs of electrons between two atoms
These bonds are created so that each atom in the molecule can have eight electrons

11. Exceptions to the Octet Rule
Atoms in the third period and below are able to accept more than eight electrons in their outer shell
Why do you think this is? Remember the rules for creating electron configuration

12. Electron Dot Notation
Recall that covalent bonding occurs between the valence electrons of atoms
The most important step of understanding covalent bonding is to be able to visualize the possibilities of electron transfer
The electron dot notation is an electron-configuration notation in which only the valence electrons are shown, indicated by placing dots around the electron symbol

13. Lewis Dot Structures of Atoms
A Lewis dot structure is a representation of the atom and the number of valence electrons around it
The chemical symbol for each element is surrounded by the amount of valence electrons, depicted as “dots”

15. Lewis Dot Structures of Atoms
Examples:
Group Element Valence Electrons Lewis Dot Structure
1A Lithium ·Li 2A 3A 4A

16. Lewis Dot Structures of Atoms
Group Element Valence Electrons Lewis Dot Structure 5A 6A 7A 8A

17. Lewis Dot Structures of Atoms
Practice Lewis Structures:
Magnesium
Aluminum
Potassium
Chlorine

18. Covalent Bonding
Tutorial to demonstrate the basics of covalent bonding: Chemical Bonding Tutorial

19. Common Molecules H· H· :O: H· ·H :O: H2O (water)
Composed of two hydrogen atom and a single oxygen atom
We will go over the rules of electron bonding later, but this is an example of how Lewis structures of atoms are used to understand chemical bonding:
H· H· :O: H· ·H
:O:
A covalent bond is composed
of two, shared electrons
Make chemical bond where two electrons are shared