Chapter 6.2 - Electronegativity and Polarity

Question 1

What is electronegativity?

Answer 1

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

Question 2

Why do electronegativity differences occur in bonded atoms?

Answer 2

1. Different nuclear charges.
2. Atoms may differ in size.
3. Shared electrons may be closer to one nucleus than the other.

Question 3

How is electronegativity measured?

Answer 3

Measured using the Pauling scale.

Question 4

What are the trends in the periodic table, when it comes to the periodic table?

Answer 4

Across a period: Increases (due to increasing nuclear charge and decreasing atomic radius).

Down a group: Decreases (due to increasing atomic radius and electron shielding).

Question 5

Why do the Pauling Scale values increase across a period?

Answer 5

Increase due to increasing nuclear charge and decreasing atomic radius.

Question 6

Why do the Pauling Scale values decrease across a group?

Answer 6

Decrease due to increasing atomic radius and electron shielding.

Question 7

What are the 4 most electronegative elements? What is the most electronegative out of these, and what is it’s value on the Pauling Scale?

Answer 7

Fluorine (4.0) is the most electronegative element.
Order of electronegativity: Fluorine > Oxygen > Nitrogen > Chlorine (Mnemonic: FONCl).

Question 8

What are the least electronegative elements?

Answer 8

Group 1 metals like lithium, sodium, and potassium.

Question 9

What electronegativity differences determine different bond types (Covalent, polar covalent and ionic)?

Answer 9

Covalent bond: Electronegativity difference = 0.

Polar covalent bond: Electronegativity difference = 0 to 1.8.

Ionic bond: Electronegativity difference > 1.8.

Question 10

What is a non-polar bond?

Answer 10

A non-polar bond occurs when the bonded electron pairs are shared equally between the bonded atoms.

Question 11

When does a bond become non-polar?

Answer 11

A bond is non-polar when:

1. The bonded atoms are of the same element.
2. The bonded atoms have similar electronegativity.

Question 12

Can you provide examples of non-polar bonds?

Answer 12

Yes. Molecules like H₂, O₂, Cl₂, and hydrocarbons like hexane (C₆H₁₄) form non-polar bonds.

Question 13

What is a polar bond?

Answer 13

A polar bond occurs when the bonded electron pairs are shared unequally between the bonded atoms.

Question 14

Can you provide an example of a polar bond?

Answer 14

Example: HCl
Hydrogen has an electronegativity of 2.1, while chlorine has an electronegativity of 3.0.
Chlorine is more electronegative, creating a dipole with δ⁺ on H and δ⁻ on Cl.

Question 15

When does a bond become polar?

Answer 15

A bond is polar when:

1. The bonded atoms are different elements.
2. The atoms have different electronegativity values.

Question 16

What is a dipole?

Answer 16

A dipole is a separation of opposite charges within a molecule caused by unequal sharing of electrons in a covalent bond.

Question 17

What are the types of dipoles?

Answer 17

Permanent dipole: A fixed separation of charge, as seen in polar molecules like HCl.
Induced dipole: A temporary separation of charge.

Question 17

When is a molecule polar?

Answer 17

A molecule is polar when the dipoles in the molecule do not cancel out, resulting in a net dipole.

Question 18

Can you give an example of a polar molecule?

Answer 18

Yes. H₂O (water):

The two O-H bonds have permanent dipoles.
The dipoles act in different directions but do not cancel out, making the water molecule polar.

Question 18

When is a molecule non-polar?

Answer 18

A molecule is non-polar when the dipoles in the molecule cancel each other out, resulting in no net dipole.

Question 19

Can you give an example of a non-polar molecule?

Answer 19

Yes. CO₂ (carbon dioxide):

The two C=O bonds have permanent dipoles.
The dipoles act in opposite directions and exactly cancel out, making CO₂ non-polar.

Question 20

How do polar solvents dissolve ionic compounds?

Answer 20

Polar solvents like water dissolve ionic compounds by surrounding the ions with oppositely charged ends of water molecules.

Question 20

Why are water molecules effective in dissolving NaCl?

Answer 20

Water is polar:

The oxygen atom has a δ⁻ charge, attracting Na⁺ ions.
The hydrogen atoms have δ⁺ charges, attracting Cl⁻ ions.

Question 20

Can you give an example of polar solvent action, using NaCl?

Answer 20

Yes. Sodium chloride (NaCl) dissolves in water as follows:

Na⁺ ions: Attracted to the δ⁻ (oxygen) end of water molecules.
Cl⁻ ions: Attracted to the δ⁺ (hydrogen) end of water molecules.
The ionic lattice breaks down, and water molecules surround the ions:
NaCl(s) + aq → Na⁺(aq) + Cl⁻(aq).