1. Covalent Bonding

2. Covalent compounds are made of molecules.
Covalent Bond: A bond between two non- metals where the atoms share valence electrons.
Covalent compound:
Made of molecules.
Molecule: a particle made up of two or more neutral atoms bonded together by covalent bonds.
Figure 2.27: Water molecules consist of two hydrogen atoms bonded to one oxygen atom.
molecule: a particle made up of two or more neutral atoms bonded together by covalent bonds
covalent bond: a strong attraction between atoms that forms when atoms share valence electrons
covalent compound: a compound that results when atoms of two or more elements bond covalently

3. Covalent Bonding Covalent bonds are similar to a game of tug of war
Each team (atom) tries to pull the rope (shared electrons) toward itself.
Neither side wins, and the bond is the rope that connects them.

4. Covalent Bonding
Formation of a covalent compound is based on achieving stability with a full valence shell
Non-metals in covalent compound share electrons to get a full valence shell
Covalent bonding satisfies the octet rule – the valence shells obtaining eight (8) electrons.
*Note period one only needs to satisfy two electrons in its valence shell.

5. Covalent Bonding Example: Water
Covalent bond is formed from a single pair of shared electrons.
Each hydrogen atom contributes a single electron to the shared pair of electrons.
Each oxygen atom contributes a single electron to the shared pair of electrons.
Hydrogen atoms (which are part of period one) achieve a full valence shell of two (2) electrons.
Oxygen atom achieves a full valence shell of eight (8) electrons.
Figure 2.30: Each hydrogen atom contributes a single electron to the shared pair of electrons in its covalent bond with oxygen.

6. Three Ways That Atoms Become Stable (Achieve a Full Valence Shell)
1) Metal atoms can lose electrons to achieve a full valence shell.
2) Non-metal atoms can gain electrons to achieve a full valence shell.
3) Non-metal atoms can share electrons with other non-metal atoms to achieve a full valence shell.

7. Three Ways That Atoms Become Stable
1) Metals can lose electrons to achieve a full valence shell
Form positive ions because they lose electrons.
Retain the same number of protons in the nucleus.
Example:
Group 1 metal ions charge: 1+ because they have lost one electron
Group 2 metal ions charge: 2+ because the lose two elections
Group 3 metal ions charge: 3+ because the lose three elections

8. Three Ways That Atoms Become Stable
2) Non-metal atoms can gain electrons to achieve a full valence shell
Form negative ions because they gain electrons
Non-metal ions end in –ide
Example:
Group 17 non-metals ion charge: 1- because they have gained one electron
Group 16 non-metal ions charge: 2- because they have gained two electron
Group 15 non- metal ion charge: 3- because they have gained three electron

9. Three Ways That Atoms Become Stable
3) Non-metal atoms can share electrons with other non- metal atoms to achieve a full valence shell - This is covalent bonding.

10. Lewis Dot Diagrams
We can use Lewis Dot Diagrams to show Covalent Bonding as well.
1) Draw a Lewis Dot Diagram of the atom
2) Show which electrons will be shared
3) Identify how many bonds they will make.

11. Lewis Dot Diagram
Show a covalent bond between two hydrogen atoms:
1) Draw the Lewis Dot Diagrams of Hydrogen
2) Show which electrons will be shared
3) Identify how many bonds they will make
One set of electrons are being shared, thus we have one bond. H . H : H

12. Lewis Dot Diagram O O O Show a covalent bond between two Oxygen atoms:
1) Draw The Lewis Dot Diagram
2) Show which electrons will be shared
3) Identify how many bonds they make
Oxygen will make two bonds, a double bond. O O O

13. Lewis Dot Diagrams
Recall: Ionic compounds are created via elements achieving stability by filling their valence shells.
The same can be said for covalent compounds. They want to achieve full valence shells.
Since elements share electrons, each bond counts as two electrons for each element.

14. Lewis Dot Diagram
Count all the electrons on the left Oxygen, you get eight; this satisfies the fact that oxygen needs eight electrons in its valence shell.
The same can be said of the oxygen on the right. O
Two electrons that count
For both oxygens
Two electrons

15. Lewis Dot Diagram NH3 PBr3 CCl4 CS2 CO2 CH4
Create Lewis dot diagrams for the following:
NH3
PBr3
CCl4
CS2
CO2
CH4

17. Properties of Covalent Compounds
Have low melting and boiling points:
Forces holding atoms together in a molecule are strong.
Bond that attract molecules to one another are relatively weak; therefore, not as much energy is needed to “break” the weak bonds. As such covalent compounds melt and boil at low temperatures.

18. Properties of Covalent Compounds
Relatively soft: weak forces between molecules mean that it’s easier for molecules to move and shift.
Poor conductors: covalent compounds do not have free electrons, and they are poor conductors of electric current and heat
Figure 2.32: Covalent compounds are poor conductors of electric current. This makes them useful as insulating covers for computer cables.

19. Diatomic Elements created by Covalent Bonds
Seven elements are made up of molecules held together with covalent bonds under normal conditions:
H2, F2, Cl2, Br2, I2: Two atoms share one electron in a covalent bond.
O2: Two oxygen atoms share two pairs of electrons to form two covalent bonds (double bond).
N2: Two nitrogen atoms share three pairs of electrons to form three covalent bonds (triple bond).

20. Network Solids
Consists of non-metal elements containing covalent bonds that connect their atoms in one large network; essentially consist of one giant molecule.
Example: Silicon dioxide (SiO2)
Figure 2.34: (A) Atoms are bonded in a regular, repeating structure by covalent bonds (B) In real quartz crystals, billions of atoms are bonded together in the same repeating structure, forming one giant molecule.

21. Network Compound Properties
Very Hard due to the strong covalent bonds throughout the lattice.
High Melting and Boiling Point as it requires an enormous amount of energy to break the bonds.
Low level of electrical conductivity since it is not an ionic bond, the moving of electrons is quite difficult.
Generally insoluble. I.E. it will remain as a solid when mixed with liquid water.

22. Network Solids: Carbon
Carbon (diamond form – network solid):
Each carbon atom is bonded to four other carbon atoms by covalent bonds.
Forms strong 3-D structure.
Carbon (graphite form – not a network solid):
Each carbon atom forms covalent bonds with three other carbon atoms, forming sheets.
Sheets are weakly attracted to each other and can slide around.
As you write on paper, layers of graphite slide off the pencil tip and onto the page.
Figure 2.35: Diamond and graphite both contain covalent bonds but have very different properties due to their structure.

23. Assignment
Worksheet
differences