1. Intermediate bonding and bond polarity
Date
Lesson Outcomes
Task 1: I can explain the meaning of the term electronegativity as applied to atoms in a covalent bond
(GRADE C)
Task 2: I can recall that ionic and covalent bonding are the extremes of a continuum of bonding type and explain this in terms of electronegativity differences leading to bond polarity in bonds and molecules, and to ionic bonding if the electronegativity is large enough
I can distinguish between polar bonds and polar molecules and be able to predict whether or not a given molecule is likely to be polar
(GRADE B)
Task 3: I can carry out experiments to determine the effect of an electrostatic force on jets of liquids and use the results to determine whether the molecules are polar or non-polar
(GRADE A)

2. BIG picture What skills will you be developing this lesson?
Numeracy
Literacy
Team work
Self management
Creative thinking
Independent enquiry
Participation
Reflection
How is this lesson relevant to every day life? (WRL/CIT)

3. What is the type of bonding in hydrogen?
Is the pair of electron shared equally by the two H atoms?
What is the type of bonding in hydrogen?
H:H
How will the electrons be shared in HCl?
In a hydrogen molecule, one pair of electrons is shared between the two hydrogen atoms. The attraction between the nuclei and electrons is same from each atom as they both are same. The pair of electrons in the bond is equally shared. These type of molecules are called NON-POLAR.

4. HCl
In a Hydrogen chloride molecule, one pair of electrons is shared between the hydrogen and chlorine atom. The attraction between the nuclei and electrons is different from each atom as they both are different. The pair of electrons in the bond is unequally shared. These type of molecules are called POLAR.

5. How do we know if the molecule is Polar or Non-polar?
We can predict the relative attracting powers of the nuclei of atoms of different elements by using the concept of electronegativity.
What is Electronegativity?

6. Electronegativity
Electronegativity is a measure of how strongly an atom or atoms attracts the bonding electrons in a covalent bond.
The higher the electronegativity, the stronger an atom's attraction for bonding electrons.
We use the Pauling Scale of Electronegativities.
It has no units and runs between 0 – 4.

7. Pauling Scale of Electronegativities
Write any three trends that you see.

8. Electronegativity Trends
What about the electronegativity of noble gases?
They have zero electronegativity as they rarely form covalent bonds and they have no electron affinity.

9. 1) Of the commonly occurring elements, this makes _________ the most electronegative and ______________the least.
2) Atoms of the same electronegativity joined by a covalent bond give an electronegativity difference of zero - i.e. H = 0. This indicates a normal nonpolar covalent bond.
Calculate the electronegativity difference between C and H.
How can we use the electronegativity difference to calculate the percentage of ionic and covalent bonding (Bond character)?

10. How to calculate the Bond character?

11. 100% covalent character
59% ionic character and 41% covalent character
89% ionic character and 11% covalent character
COVALENT
POLAR
IONIC
What is the relation between electronegativity difference and percentage ionic character?

13. Questions?

14. Answers

15. Polar covalent bond
Non-Polar covalent bond
Polar covalent bond

16. Polarisation of Ionic bond
Ionic bonds can be polarised by the cations strongly attracting the outer shell electrons of the anion.
What does the polarising power of a cation depend on?
Its charge density, which depends on the size of the ions and its charge.
Smaller the ionic radius/greater the charge – the greater the charge density.
For an anion, larger the radius, more easily polarised it is.

17. Questions
CLUE: Ionic compounds tend to have high melting and boiling points and dissolve in polar solvents only.

18. Answers 1 HF as there biggest difference in electronegativity. 2
3 Difference in electronegativity between lithium and iodine is 1.5 ( ).
From Table 2.1.1, percentage ionic character = 43%.
So possibly lower melting and boiling points, and soluble in an organic solvent.

19. How can I improve on task 1?
Task 1: Review
Go back to your lesson outcome grid and fill out the ‘How I did’ and the ‘Targets’ column.
Lesson Outcomes
How I did
Targets
Task 1:
Grade C
Met?
Partly met?
Not met?
How can I improve on task 1?

20. What is a dipole?
Dipole = a molecule (or part of a molecule) with a positive end and a negative end.
E.g. HCl molecules have a dipole.
When a molecule has a dipole it is polarised.

21. Dipole Moment
Polarity of a molecule is measured as Dipole moment.
It is defined as the product magnitude of charge on the atoms and the distance between the two bonded atoms. Its common unit is debye D.
Direction of the polar bond in a molecule:
Arrow points toward the more electronegative atom.
Is it possible to have several polar bonds in a molecule?
Does this make the whole molecule polar?
H Cl + -

22. Determining Molecular Polarity
Nonpolar Molecules
Dipole moments are symmetrical and cancel out.
BF3 F B

23. Determining Molecular Polarity
Polar Molecules
Dipole moments are asymmetrical and don’t cancel .
H2O H O
net
dipole
moment
Resultant dipole
Because water is an angular molecule the dipoles do not cancel and a resultant dipole moment is produced.

24. Molecules with 3 Atoms CO2 HCN SO2
Even though the C-O bond is polar, the bonds cancel each other out because the molecule is linear the dipole moments are equal and in opposite directions.Therefore CO2 is non-polar.
CO2
The dipole moment between H-C points in the direction of C. The dipole moment points between C-N points in the direction of the N. Therefore the dipole vectors are additive and HCN is polar
HCN
SO2
SO2 is a polar molecule because the S-O dipole Moments don’t cancel each other out due to the angle

25. Determining Molecular Polarity
Therefore, polar molecules have...
asymmetrical shape (lone pairs) or
asymmetrical atoms
CHCl3 H Cl
net
dipole
moment

26. Molecules with 4 Atoms Non-polar CCl4 is non-polar Polar
CHCl3 is polar

27. Which of the following molecules are polar (have a
dipole moment)?H2O, CO2, SO2, and CH4 O H S O
dipole moment
polar molecule
dipole moment
polar molecule C H C O
no dipole moment
nonpolar molecule
no dipole moment
nonpolar molecule
10.2

28. Polar or non-polar? ? ?

29. How can I improve on task 2?
Task 2: Review
Go back to your lesson outcome grid and fill out the ‘How I did’ and the ‘Targets’ column.
Lesson Outcomes
How I did
Targets
Task 2:
Grade B
Met?
Partly met?
Not met?
How can I improve on task 2?

30. Experiment
To carry out experiments to determine the effect of an electrostatic force on jets of liquids and use the results to determine whether the molecules are polar or non-polar
Equipment & chemicals:
Burette with filling funnel
Glass rod and dry piece of cloth
Beaker, 600 cm3, or large diameter container
A range of organic hydrocarbons, alcohols and ketones for which hazard information is available,
50 cm3 each

31. Procedure

32. New Information for Task 3

33. Observations and interpretations
What happens to the jet of your liquid?
What happens with other liquids?
Why does this happen?

34. How can I improve on task 3?
Task 3: Review
Go back to your lesson outcome grid and fill out the ‘How I did’ and the ‘Targets’ column.
Lesson Outcomes
How I did
Targets
Task 3:
Grade A
Met?
Partly met?
Not met?
How can I improve on task 3?

35. Review

36. Homework Homework task: Due date: Criteria for Grade C:
Criteria for Grade B:
Criteria for Grade A/A*:

37. Information
Properties of Covalent compounds: Properties of Ionic compounds:

38. Polar Bonds .. .. .. F O N H Cl H H H B H H F F Polar Polar Nonpolar
Students often confuse electron-domain geometry with molecular geometry.
You must stress that the molecular geometry is a consequence of the electron domain geometry.
The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them. Cl H Xe C C Cl F F Cl H F F Cl H
Polar
Nonpolar
Nonpolar
Polar
A molecule has a zero dipole moment because their dipoles cancel one another.