1. Form an ionic bond between the following
Na and Cl
Cl and F
Na and Mg
Mg and Br
NH4+ OH-
NH4+ SO42-

2. Covalent Bonding

3. The Octet Rule
The octet rule says that atoms tend to gain, lose or share electrons so they have eight electrons in their outer shell.

4. Covalent Bonding
Instead of gaining or losing electrons atoms can get stable by sharing electrons
This is always between two non-metals.
Two fluorine atoms, for example, can form a stable F2 molecule in which each atom has 8 valence electrons by sharing a pair of electrons.
In covalent bonds they can share
more than two electrons

5. Single, Double and Triple Bonds
With Covalent bonds the elements can share two or more electrons
A Single Bond is when 2 electrons are shared they are represented by a single line in bond diagrams
A Double bond is when 4 electrons are shared they are represented by two lines in bond diagrams
A Triple bond is when 6 electrons are shared they are represented by three lines in bond diagrams

6. Oxygen has six valence electrons and is seeking an octet
Oxygen has six valence electrons and is seeking an octet. Therefore it combines with two hydrogen atoms, each with one valence electron.

7. Representing covalent molecules
Chemists use two types of diagrams to represent molecules:
1. Electron dot formula (Lewis structure) – each outer shell (valence) electron is represented by a dot.
2. Valence structure – lines are used to represent electrons: one line represents one pair of electrons.

8.            
Lewis Dot Structure
In order to draw covalent bonds you must be able to write Lewis Dot structure
This shows the number of valence electrons around the symbol
Put one electron on each side before doubling up.
We can see that helium does not follow this rule exactly.

9. First, we must determine whether CO2 is a covalent or ionic bond.
Because nonmetals form covalent bonds, CO2 will be covalent.
Ionic bonds form when combining both metals and a nonmetals.
Begin by drawing the Lewis dot structure of each individual atom.
How many electrons does the carbon want? 4
How many electrons does each oxygen want? 2

10. Determine which is the central atom
All three of these atoms want an octet.
Carbon needs to “share” four electrons.
Carbon will share two of its electrons with the oxygen on the right and two with the oxygen on the right.

11. :C: The carbon dioxide Lewis Dot Structure: :C:
Take note of the boxed in electrons below.
:C:
Now each atom has eight electrons.
What type of bonds does CO2 have?
Double bonds

12. Draw and complete the following table
Name/
Formulae
No. Valence electrons
E dot diagram
Bond diagram
Type of bond
HCl
H = 1
Cl = 7
Methane CH4
C = 4
Oxygen (02)
O =
Include the following compounds CS2, NH3 , CF4.

13. Naming Covalent formulas
First name generally stays the same.
Second non metal name changes to –ide.
If there is one or more of the second element it will have prefix in front
e.g. Mono (means 1) or di (2) or tri (3) tetra (4) penta (5) e.g. CO2 Carbon Dioxide
If there are two or more of the first element it must have a prefix
e.g. di (2) or tri (3) tetra (4) penta (5) Dihydrogen sulfide (H2S)

14. Naming Covalent compounds
What is dihydrogen monoxide?
H2O
Name CO
Carbon Monoxide
Name P2S3
Diphosphourous trisulfide

15. Pair of bonding electrons
Valence electrons
In covalent bonds when electrons are shared the electrons spend most of their times between the two nuclei of the atoms. The electrons are called localised electrons.
The shared electrons are called the bonding electrons
The valence electrons not involved in bonding are called the non-bonding electrons.
Pairs of non-bonding electrons
are called lone pairs.
Lone pair
Pair of bonding electrons

16. Your turn How many bonding electrons does Cl2 have?
How many non-bonding electrons does Cl2 have
How many lone pairs does Cl2 Have?

17. Covalency
Chlorine needs to share one electron to give it a stable outer shell. Therefore its has a covalency of one.
The covalency of an atom is generally the number of electrons it shares when bonding with another non metal atom.

18. Draw and Complete the following table
Name/
Formulae
No. bonding electrons
No. of non bonding electrons
No. of lone pairs
Covalency
Fluorine (F2)
Methane CH4
C =
H =
Oxygen (02)
Include the following compounds HCl, CS2, NH3 , CF4.

19. Charge Cloud Model
This Model of the atom pictures the electrons moving around the nucleus in a region called an electron cloud.
The electron cloud is a cloud of varying density surrounding the nucleus. The varying density shows where an electron is more or less likely to be.
an 'electron cloud' may be a single, double or triple bond, or a lone pair of electrons

20. What is the Electron Cloud Model? Diagram 1:

21. What is the Electron Cloud Model? Diagram 2:

22. Shapes of molecules
The shape of a molecule describes the way in which the atoms are arranged
Molecules can be linear, angular v-shaped or bent, triangular pyramid and tetrahedral.
There are more shapes but you only need to the know the above

23. Shape of Molecule
Name of Shape
No. of Lone pairs
Bond angle
Examples
Linear
180
CO2, HCN
Bent/
Angular 2
<109.5
H2O, SCl2
Triangular pyramid 1
NH3, PCl3
Tetrahedral
109.5
CH4, SiF4

24. Activity Trigonal Planar 0 120° sulfur trioxide
The molecule is all in the same plane
and is two dimensional.
Use Balloons and string to make the shape of a molecule you have been assigned
Use the molecular models to make all the other shape molecules
Activity

25. x

26. Valence Shell Electron Pair Repulsion Theory
Trigonal Planar
Valence Shell Electron Pair Repulsion Theory
Tetrahedral
Trigonal bipyramidal
Octahedral

27. The valence shell electron pair repulsion (VSPER) model
VSPER is used for predicting the shapes of individual molecules, based upon the extent of electron-pair repulsion (to push away).
a lone pair of electrons is a non-bonding pair of electrons
'electron clouds' are negatively charged since the electrons are negatively charged, so electron clouds repel (push away) from one another and try to get as far away from each other as possible.

28. The valence shell electron pair repulsion (VSPER) model
RULES
1. Lone electron pairs in the outer shell of an atom in a molecule will repel each other the most due to their negative charge
2. lone pairs of electrons exert a greater repelling effect than bonding pairs do
3. lone pair-bonding pair repulsion is greater than bonding pair-bonding pair repulsion
lone pair-lone pair repulsion > lone pair-bonding pair repulsion > bonding pair-bonding pair repulsion

29. How to determine shapes of molecules
1. Decide which atom is the central atom
2. Determine the number of valence electrons for each atom
3. Arrange the electrons to include bonding
4. Draw the bonding electrons and lone pairs so they are as far apart as possible
5.Count the total number of electron pairs around the central atom, including both the bonding pairs and lone pairs. Double and triple bonds are counted as on bonding pair.
6. Use the VSEPR geometry table to predict the geometry of the molecule (it can only be one of 5 shapes!!).

30. How to determine shapes of molecules
Sometimes the molecules are represented by AXY, A is the central atom, X is the 2nd atom and Y is the # of peripheral atoms
AX2 = linear or bent
AX3 = trigonal planar or trigonal pyrimadial
AX4 = tetrahedral (tetra = 4 faces)
AX5 = trigonal bipyramidal (2 pyramids)
AX6 = octahedral (octa = 8 faces)

31. Which shapes do you recognise?x

32. Your turn
Use Lewis structures, VSPER and the molecular models to help you determine the shape of the following molecules.
Carbon tetrachloride
Silicon disulfide
Dicarbon dihydride
Boron trihydride
Phosphorous trifluoride

33. What is Electronegativty?
Electronegativity: is a measure of an elements ability to attract electrons
The electronegativity of elements tends to increase from left to right across a period.
Electronegativities decrease from top to bottom within a group.
Fluorine is the most electronegative atom

34. Electronegativity Values
The electronegativity values can be found in the periodic table
The higher the value the higher the electrotnegativity
The Pauling scale is used to measure electronegativity. It is a relative scale running from 0.7 to 4.0 (hydrogen = 2.2).
The units for electronegativity are Pauling units.

35. x

36. There are two types of covalent bonding
1. Non-polar bonding with an equal sharing of electrons.
2. Polar bonding with an unequal sharing of electrons. The number of shared electrons depends on the number of electrons needed to complete the octet.

37. 1. Non Polar Bonds What does polarised/polarity mean? Opposites
Non polar bonding results when two identical non-metals equally share electrons between them.
One well known exception to the identical atom rule is the combination of carbon and hydrogen in all organic compounds.
Non polar bonding exists between carbon and hydrogen

38. Iodine (I2) and oxygen (O2) forms a diatomic (di – two, atomic – atoms) non-polar covalent molecule.

39. x

40. 2. Polar Bonds
Polarised bonds occur in covalent molecules. One atom has greater electronegativity and therefore has a partial (slight) negative charge because it attracts the bonding electrons more strongly (remember electrons have a –ive charge).
The other atom has a slight
positive charge.

41. Partial positive is represented by this symbol
Partial negative
is represented
By this symbol

42. x

43. Which is more electronegative H or Cl?
Cl has greater electronegativity
The bonding electrons therefore spend more time near the Cl atom
So the Cl side of the molecule becomes slightly negative (partial negative
charge) and the H side becomes
slightly positive making a
polarised bond
What about HF?

44. Polar molecules
Polar molecules are those containing polar bonds that do not cancel each other out
Molecular polarity is dependent on the difference in electronegativity between atoms in a compound and the asymmetry of the compound's structure.
For example, a molecule of water is polar because of the unequal sharing of its electrons in a "bent" structure, whereas methane is considered non-polar because the carbon shares the hydrogen atoms uniformly.

45. Polar
The covalent bond between HCl is said to be polarised and the molecule is called a polar molecule
It is also said to be a dipole
because is has two charged ends

46. Non polar molecules
Non polar molecules are those that contain only non-polar bonds OR
Molecules in which polar bonds cancel each other out

47. Youtube clip

48. Quiz What happens to the electrons in a polar bonds?
How do you know if a bond is polar?
What is a non polar molecule?
What is a dipole?
What is the symbol for slightly negative?
Can non polar molecules have polar bonds?

49. How to determine polar molecules
There are two important factors
1. The polarity of the individual bonds in the molecule;
2. The shape or geometry of the molecule.
Steps to take
Determine if a given individual bond is polar, Look at the difference between electronegativity of the atoms in the perioidc table. If the difference is:
0.3 < non polar
= polar

50. b) Determine the shape of molecule. Then there are 3 option
i) if all bonds are non-polar, then the whole molecule is non-polar regardless of its shape.
ii) If there is symmetry in the molecule so that the polarity of the bonds cancels out, then the molecule is non-polar. (symmetry arround the central atom)
iii) If there are polar bonds but there is no symmetry the overall molecule is polar.

52. Which molecules are polar?

53. Determine if BF3 is polar or non polar
B-F bonds are polar but they are symmetrically arranged around the central fluorine atom. No side of the molecule has more negative or positive charge than another side, and so the molecule is nonpolar.

54. Predict whether the following molecules are polar or nonpolar: (a) BrCl; (b) SO2;
SOLUTION (a) Chlorine is more electronegative than bromine. Consequently, BrCl will be polar with chlorine carrying the partial negative charge:
(b) Because oxygen is more electronegative than sulfur, the molecule has polar bonds.
For each of these, the VSEPR model predicts a bent geometry. Because the molecule is bent, the bond dipoles do not cancel and the molecule is polar

55. Which of the following molecules contains polar bonds but is nonpolar?
NH3 F2
CCl4
CH2Cl2

56. In CCl4, there are 4 bonds arranged symmetrically around the central carbon atom.
Each bond is polar, you can tell due to the electronegativity differences between carbon and chlorine.
Because the 4 atoms of chlorine are arranged symmetrically, the polarity of the bonds cancel each other out, making a non-polar molecule.

57. Determine if OF2 is polar or non polar
The electronegativities of oxygen and fluorine, 3.44 and 3.98, respectively, produce a 0.54 difference that leads us to predict that the O-F bonds are polar. The molecular geometry of OF2 is bent. Such an asymmetrical distribution of polar bonds would produce a polar molecule.

58. When there are no polar bonds in a molecule, there is no permanent charge difference between one part of the molecule and another, and the molecule is nonpolar.

59. What is the difference between a polar bond and a polar molecule?
A polar bond is a charged bond. There is a positive and negative end that do not cancel each other out
A polar molecule contains polar bonds that do not cancel each other out.