8. ELECTRON NEGATIVITY

Question 1

1. How would you describe electronegativity?

Answer 1

• it is the power of an atom in a molecule to attract a bonding pair of electrons towards itself
• it determines how shared electrons are distributed
• A measure of the tendency of an atom to attract a bonding pair of electrons


Question 2

2. How and where in the periodic table does the electronegativity increase?

Answer 2

• the electronegativity increases down the up the group
• it increases across the period (from left to right)
• metals have lower electronegativites
• non metals have higher electronegativities

Question 3

3. What is the electronegativity of the following elements?

3.1: Hydrogen
3.2: Carbon
3.3: Nitrogen
3.4: Oxygen
3.5: Fluorine
3.6: Chlorine
3.7: Bromine
3.8: Iodine

Answer 3

3.1: 2.1
3.2: 2.5
3.3: 3.0
3.4: 3.5
3.5: 4.0
3.6: 3.0
3.7: 2.8
3.8: 2.5

Question 4

4. What is the result of the electronegativity when two atoms that have a non-polar bond to one another?

Answer 4

• the atoms pull at the shared electrons with the same strength
• the electronegativity is zero

Question 5

5. What is the result of the electronegativity when two atoms have a polar bond to one another?

Answer 5

• the atoms pull at the shared electrons with a greater strength
• each connected atom pulls with a different strength
• the electronegativity is greater than zero

Question 6

6. What do all polar bonds have?

Answer 6

• they have a degree of ionic character
• the percentage of ionic character is related to the strength of the electronegativity between the atoms
• the percentage ionic character and the electronegativity difference are proportional
  (when one increases, so does the other)
• is worked out by this graph:

Question 7

7. What is the percentage of ionic character between two atoms bonded together by a pure non-polar covalent bond?

Answer 7

• the electronegativity difference between the two atoms is zero
• the percentage of the ionic character is zero
• the percentage of covalent character is 100%

Question 8

8. What happens if the electronegativity difference between two atoms is 1.7?

Answer 8

• the two atoms are polar covalently bonded together
• they have a 50% ionic character
• they have a 50% covalent character

Question 9

9. What does the curve on this graph indicate?

Answer 9

• it indicates that all polar covalent bonds always have some degree of ionic and covalent character
• they can never be 100% ionic

Question 10

10. What is the percentage of ionic character in HCL?

Answer 10

• H has an electronegativity of 2.1
• Cl has an electronegativity of 3.0
• ▵Electronegativity= 3.0-2.1
  = 0.9
• it has a 15% ionic character
• it has an 85% covalent character

Question 11

11. How would you write partial negative and partial positive charges?

Answer 11

• δ +
• δ -

Question 12

12. Why do partial charges arise?

Answer 12

• all the polar covalent bonds have some degree of ionic character

Question 13

13. Which element is always partially negatively charged (δ-)?

Answer 13

• the one with the greater electronegativity

Question 14

14. Do polar bonds result in polar molecules?

Answer 14

• no, polar bonds can result in non-polar molecules

Question 15

15. How do the arrows (linear geometry) signify the polarity of the CO2 molecule?

Answer 15

• O has a higher electronegativity than C
• that is why the arrow points from C to O
• it points from an element of lower electronegativity to an element of higher electronegativity
• the magnitudes of the arrows are equal in value
• they face in the opposite direction of one another
• this means that they cancel each other out
• the CO2 molecule does not have an overall polarity
• it is non polar

Question 16

16. How do the arrows (linear geometry) signify the polarity of the H2O molecule?

Answer 16

• the O has a higher electronegativity than the H
• the arrows points from H towards O
• the arrows are of equal magnitude
• they do not point in opposite directions
• when added together
• they cannot cancel each other out
• the molecule has an finite (nonzero) net dipole
• it is a polar molecule

Question 17

17. How do the arrows (linear geometry) signify the polarity of the HCCl3 molecule?

Answer 17

• Cl is more electronegative than C
• the three bond dipoles (arrows) point downwards towards the Cl atoms
• between C and H, C is more electronegative
• the bond dipole (arrow) points down towards the C atom
• all the bond dipoles (arrows) point downwards
• they will not be able to cancel each other out
• the molecule is polar

Question 18

18. How do the arrows (linear geometry) signify the polarity of the CCl4 molecule?

Answer 18

• Cl is more electronegative than C
• we have 4 bond dipoles (arrows) of equal magnitude
• they are acting in opposing directions
• when we add these bond dipoles (arrows) together
• they cancel out
• the bond is non-polar

Question 19

19. What does each polar molecule have?

Answer 19

• a dipole moment

Question 20

20. What will a higher dipole moment result in?

Answer 20

• a more polar molecule

Question 21

21. What is a dipole moment?

Answer 21

• it is a measure of polarity
• it is important for deciding what solvent to use to dissolve a substance

Question 22

22. What kind of solvents do polar and non-polar substances dissolve in?

Answer 22

• polar substances dissolve in polar solvents
• non-polar substances dissolve in non-polar solvents
• this is why water and oil do not mix

Question 23

23. What is necessary to know in order to predict whether a molecule will be polar or non polar?

Answer 23

• we need to know its three dimensional geometry
• this is seen after drawing the Lewis Structures

Question 24

24. What do Lewis Structures represent?

Answer 24

• they represent how the valence electrons of the central atom are distributed as bonds and lone pairs

Question 25

25. Read through the summary.
    Does everything make sense?

Answer 25

• yes