6.2 - Electronegativity & Polarity

Question 1

In a covalent bond, what do the nuclei of the bonded atoms attract?

Answer 1

The shared pair of electrons

- When the atoms are the same, the attraction is equal so the electrons stay in the middle (equidistance from each atom)

Question 2

Under what circumstances may a pair of electrons tend towards one of the atoms?

Answer 2

• When the nuclear charges are difference

- When the atoms are different sizes

Question 3

Define electronegativity.

Answer 3

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

Question 4

What is the Pauling Scale?

Answer 4

Compares the electronegativity of atoms

Question 5

When does electronegativity increase?

Answer 5

Electronegativity increases when nuclear charge and atomic radius increases

Question 6

What is the most electronegative element, and what are the most and least electronegative elements?

Answer 6

Flourine is most electronegative (value 4.0)

Non-metals most electronegative (e.g. O, F, N, Cl)
Group 1 metals least electronegative
As you go down groups, electronegativity decreases

Question 7

What are non-polar bonds?

Answer 7

Bonds are non-polar when the bonded atoms are the same, meaning they have similar/same electronegativity so they are pure covalent bonds.

Question 8

What electronegativity values determine whether the bond type is covalent, polar covalent or ionic.

Answer 8

0 - Covalent
0-1.8 - Polar covalent
1.8+ - ionic

Question 9

What is a polar bond?

Answer 9

Bonds are polar when the electron pair is shared unequally

• Due to difference in electronegativity (polar covalent bond)
• Causes partial charges to each of the bonded atoms
• This separation of opposite charges is referred to as a dipole

Question 10

How can you determine if a molecule with dipoles is a polar or not?

Answer 10

Some molecules have 2 or more dipoles, this may enforce a larger dipole over the whole molecules.

If the dipoles work in exact opposite directions, they cancel each other out, like in CO2
But in H2O, the molecule has an overall dipole, as the dipoles do not counteract each other.

Question 11

Explain solubility and polar solvents.

Answer 11

NaCl + aq > Na+ + Cl-

• Due to the polarity of water molecules, they attract the Na and Cl ions, breaking down the ionic lattice
• This results in water molecules surrounding the ions.