6.2 Electronegativity and polarity

Question 1

When elements are the same, the bonded electron pair is shared evenly, this changes when the elements are different:

Answer 1

The nuclear charges are different
The atoms may be different sizes
The shared pair of electrons may be closer to one nucleus than the other

Question 2

What is electronegativity

Answer 2

The attraction of a bonded atom for the pair of electrons in a covalent bond

Question 3

What is the Pauling scale used for

Answer 3

Comparing the electronegativity of the atoms of different elements

Question 4

How do the Pauling electronegativity values depend on their positions in the periodic table

Answer 4

Across the table, the nuclear charge increases and the atomic radius decreases
Electronegativity increases up the periodic table

Question 5

What does a large Pauling value indicate

Answer 5

That atoms of the element are very electronegative

Question 6

Which part of the periodic table have the most electronegative atoms

Answer 6

The non-metals nitrogen, oxygen, fluorine and chlorine

Question 7

Which part of the periodic table have the least electronegative atoms

Answer 7

The group 1 metals including lithium, sodium and potassium

Question 8

If the electronegativity difference in large, what happens to the attraction between atoms

Answer 8

The bonded atom will have a much greater attraction for the shared pair than the other bonded atom
The more electronegative atom will have gained control of the electrons and the bond will now be ionic rather than covalent

Question 9

Electronegativity difference of covalent bonds

Answer 9

0

Question 10

Electronegativity difference of polar covalent bonds

Answer 10

0 to 1.8

Question 11

Electronegativity difference of ionic bonds

Answer 11

Greater than 1.8

Question 12

A bond will be non-polar when

Answer 12

The bonded electron pair is shared equally between the bonded atoms
The bonded atoms are the same
or
The bonded atoms have the same or similar electronegativity

Question 13

What is a pure covalent bond

Answer 13

When the molecule comes from bonded atoms of the same element

Question 14

What happens in a polar bond

Answer 14

The bonded electron pair is shared unequally between the bonded atoms.

Question 15

When will a bond be polar

Answer 15

When the bonded atoms are different and have different electronegativity values, resulting in a polar covalent bond

Question 16

Example of a polar bond - hydrogen chloride

Answer 16

HCl has atoms of different elements
H has electronegativity 2.1
Cl has electronegativity 3.0
The chlorine atom is MORE electronegative than the hydrogen atom
The chlorine atom has a greater attraction for the bonded pair of electrons than the hydrogen atom, resulting in a polar covalent bond
The H-Cl bond is polarised with a small partial + charge on the H and a small - on the Cl

Question 17

What does 𝛿 mean

Answer 17

Lower case delta meaning small

Question 18

What are the partial charges

Answer 18

𝛿+
𝛿-

These are much smaller than the full + and - charges

Question 19

What is a permanent dipole

Answer 19

A dipole in a polar covalent bond does not change and is called a permanent dipole to distinguish it from an induced dipole

Question 20

Depending on the _____ of a molecule, the dipoles may _____ one another to produce a larger dipole over the whole molecule, or _____ ___ if the dipoles act in opposite directions

Answer 20

Shape
Reinforce
Cancel out

Question 21

What charge does the atom with the larger electronegativity value have

Answer 21

𝛿-

Question 22

What charge does the atom with the smaller electronegativity value have

Answer 22

𝛿+

Question 23

Example of a polar molecule - water

Answer 23

The two O-H bonds each have a permanent dipole
The two dipoles act in different directions but do not exactly oppose one another
Overall the oxygen end of the molecule has a 𝛿- charge and the hydrogen end has a 𝛿+ charge

Question 24

Example of a non-polar molecule - carbon dioxide

Answer 24

The two C=O bonds each have a permanent dipole
The two dipoles act in opposite directions and exactly oppose one another
Over the whole molecule, the dipoles cancel and the overall dipole is zero

Question 25

What is a dipole

Answer 25

A separation in electrical charge so that one atom of a polar covalent bond or one end of a polar molecule has a small positive charge 𝛿+ and the other has a small negative charge 𝛿-

Question 26

What is a dipole-dipole force

Answer 26

An attractive force between permanent dipoles in neighbouring polar molecules