1. Chapter 8 Intro to Chemistry
Covalent Bonding

2. Why do atoms bond It’s all about stability
Atoms want to achieve the stable octet of the noble gases
Ionic bonds achieve this octet through an exchange of electrons
The exchange occur between a metal ion (cation) and a non-metal ion (anion)
Covalent bonds are different

3. What is a covalent bond
A covalent bond occurs when atoms share electrons
Covalent bonds occur between two non-metals
Valence electrons play a role in covalent bonds

4. Molecules and Molecular Compounds
Molecule – a neutral group of atoms joined together by a covalent bond.
Diatomic molecule – a molecule consisting 2 of the same element. Example: O2
Molecular compound – a compound composed of molecules. (covalently bonded atoms).

5. The Diatomic Elements
The elements Hydrogen, Nitrogen, Fluorine, Oxygen, Iodine, Chlorine, and Bromine are always found as diatomic molecules:
HONClFIBr (say HONKLE-fibber)
BrINClHOF (say Brinckle-hoff)
I Have No Bright Or Clever Friends
There are seven such elements. The first one is the first element Hydrogen; the rest form a 7 on the periodic table: N, O, F across, then going down Cl, Br, I.

6. Characteristics of Molecular Compounds (elements that are bonded covalently)
Lower melting points and boiling points than ionic compounds.
Most are gases or liquids at room temperature.
Are composed of atoms of 2 or more nonmetals.

7. Molecular Formulas
A molecular formula shows how many atoms of each element a molecule contains.
Ex: H2O has 2 hydrogen atoms and oxygen atom
You can represent a molecule by its molecular formula, structural formula, space-filling molecular model, perspective drawing or by a ball-and-stick molecular model.

8. Different ways to represent a molecule:
Structural formula
Perspective drawing
Molecular Formula
NH3
Ball-and-stick molecular model
Space-filling molecular model

9. How to determine a covalent bond
In the case of hydrogen combining to form H2
Each hydrogen has 1 valence electron
In order to achieve the noble gas configuration of helium, they each need two valence electrons
H2 achieves this by sharing their valence electrons and forming a bond

11. What happens in a covalent bond
In a covalent compound, electrons are shared between atoms to form a covalent bond in order that each atom in the compound has a share in the number of electrons required to provide a stable, Noble Gas, electronic configuration (octet rule).
Each atom “thinks” it has a full outer shell containing 8 valence electrons
The sharing of electrons is what makes the bond and holds the atoms together

12. Lewis Structures and Covalent Bonds
Electrons in the Lewis Structure (electron dot diagram) are paired to show the bonding pair of electrons.
Often the shared pair of electrons forming the covalent bond is circled
Sometimes the bond itself is shown with a dash (-)
A pair of valence electrons that is not shared between atoms is called an unshared pair, lone pair or non-bonding pair.

13. Water – Is an example of a covalent compound.
Hydrogen needs 2 electrons to fill its outermost shell
Oxygen needs two electrons to fill its outermost shell

14. Lewis Structure of Water (single covalent bonds)

15. Lewis Structure of Carbon Dioxide: CO2 (Double covalent bonds)
Carbon has four valence electrons, and oxygen has six.
Each pair of shared electrons forms a single bond
A bond that involves two shared pairs of electrons is called a double covalent bond.

16. Lewis Structure of Nitrogen (triple covalent bonds)
T A bond formed by sharing 3 pairs of electrons is called a triple covalent bond. + =

17. Covalent Compounds
Covalent Bonding

18. You Try It
What would the formula be for a compound containing carbon and fluorine
What is the formula for a compound containing nitrogen and oxygen
Carbon and hydrogen?
Antimony and bromine?
Chlorine and oxygen?

19. Bond Dissociation Energies
Covalent bonds are extremely strong! It would take 435 KJ of energy to break apart 1 mole (about 2 grams) of a hydrogen molecule (H2).
The energy required to break a covalent bond is known as the bond dissociation energy.
A single bond has a lower bond dissociation energy than a double bond or a triple bond.

20. Resonance Structures
A resonance structure occurs when there is more than one valid Lewis structure for a molecule or ion
Resonance structures differ only in the position of the electron pairs, never in the position of the atoms

21. Lewis Structure of Ozone (O3)
Begin by drawing the basic structure
Then add the third bond
However, we cannot be sure if the double bond is on the left or the right
Draw the resonance structures for ozone

22. You Try It
Draw resonance structures for
SO2

23. Naming Covalent Compounds
Simple covalent compounds are generally named by using prefixes to indicate how many atoms of each element are shown in the formula
The ending of the last (most negative) element is changed to -ide.

24. Prefixes
The prefixes used are mono-, di-, tri-, tetra-, penta-, hexa-, and so forth
The mono- prefix is not used for the first element in the formula
The "o" and "a" endings of these prefixes are dropped when they are attached to "oxide."
Monoxide
Hexoxide
Pentoxide

25. Table of Prefixes 1
Mono- 2
Di- 3
Tri- 4
Tetra- 5
Penta- 6
Hexa-

26. Which Element is First?
Generally, they are in the same left-to-right order that they have on the periodic table
Except that you would have to squeeze hydrogen in between nitrogen and oxygen

27. Name the following compounds
PH3
phosphorus trihydride CO
carbon monoxide HI
hydrogen monoiodide 
N2O3
dinitrogen trioxide

28. What is the Formula Carbon Tetrachloride Dinitrogen Pentoxide
CCl4
Dinitrogen Pentoxide
N2O5
Silicon Tetrabromide
SiBr4