Structure and Bonding

Question 1

What are covalent bonds?

Answer 1

Formed when non-metal atoms share pairs of electrons.

Question 2

What is pure covalent bonding?

Answer 2

When two atoms share bonding electrons equally, as they both have the same attraction for the bonding electrons - same electronegativity value.

Question 3

Give two examples of a pure covalent bond.

Answer 3

Cl - Cl and P - H

Question 4

What is a permanent dipole?

Answer 4

Formed between elements with different electronegativity values, meaning one atom will have a greater attraction for bonding electrons than the other creating a slightly negative 𝛿- atom and a slightly positive 𝛿+ atom.

Question 5

What is polar covalent bonding?

Answer 5

Bonding where there is a permanent dipole.

Question 6

Give two examples of a polar covalent bond.

Answer 6

H - Cl and O - Cl

Question 7

The general rule of polar bonds is…

Answer 7

Electronegativity difference LESS THAN 2 means the bond is COVALENT.
The closer to 2, the more polar; the closer to 0, the less polar.

Question 8

What is a common example of an extremely polar bond?

Answer 8

H - F

Question 9

Electronegativity value differences greater than 2 indicate…

Answer 9

That the electron movement from the atom with a lower value to the higher value atom is complete, resulting in the formation of ions. Therefore indicating that ionic bonding is present.

Question 10

Which compound is considered the most ionic?

Answer 10

Caesium fluoride with an electronegativity value difference of 3.2.

Question 11

How do ionic lattices exist?

Answer 11

As giant lattices in which the oppositely charged ions attract each other. The electrostatic attraction is not in any particular direction.

Question 12

Name two examples of ionic compounds.

Answer 12

NaCl and CsCl

Question 13

Describe the order of the bonding continuum with reference to the electronegativity value differences.

Answer 13

Diff 3.0 - ionic
Diff ~1.5 - polar covalent
Diff 0.0 - pure covalent

Question 14

What does the name ‘bonding continuum’ suggest?

Answer 14

Bonding gradually changes as the difference in electronegativity between atoms increases - there is no sharp distinction between ionic and covalent bonds.

Question 15

What are intermolecular forces?

Answer 15

Forces acting between molecules, known as van der Waals forces.

Question 16

What are the three types of intermolecular forces?

Answer 16

London dispersion forces, permanent dipole - permanent dipole interactions, and hydrogen bonding.

Question 17

When do permanent dipole - permanent dipole interactions occur?

Answer 17

Between polar molecules.

Question 18

Give two examples of polar molecules.

Answer 18

HCl and H20

Question 19

Give two examples of non-polar molecules.

Answer 19

CO2 and CCl4 - because of their symmetrical shape.

Question 20

When doing the charged rod experiment, what do the outcomes mean?

Answer 20

Polar substances, like water, are attracted to the charged rod, whereas non-polar substances, like heptane, are not.

Question 21

Order the intermolecular forces by strength, from weakest.

Answer 21

LDFs, permanent dipole - permanent dipole interactions, hydrogen bonding.

Question 22

When does hydrogen bonding occur?

Answer 22

When hydrogen is bonded to highly electronegative elements, such as fluorine, oxygen, and nitrogen.

Question 23

Why does hydrogen bonding occur?

Answer 23

The H atom is so small that the positive charge on the atom is unusually high making the bond highly polar. The electrons in the bond are more strongly attracted away from the hydrogen atom resulting in a very strong permanent dipole - permanent dipole interaction between molecules.

Question 24

Effect of hydrogen bonding on melting and boiling points?

Answer 24

Much higher than compared with other elements in the same group.

Question 25

What gives water its unusual properties?

Answer 25

Hydrogen bonding

Question 26

What are some unusual properties of water?

Answer 26

• When cooled, water expands making it less dense than liquid water, explaining why ice floats on water. This is due to the ordering of the molecules into an open structure, with an increase of hydrogen bonds.
• Water is more viscous compared to substances that do not contain hydrogen bonding.
• Without hydrogen bonding, the boiling point of water would be well below 0 degrees.
• Water is able to dissolve a wide range of substances due to the high polarity of the bonds within it - mainly polar and ionic substances.

Question 27

What does (aq) mean?

Answer 27

Used to indicate that ions are hydrated in solution.

Question 28

What is the general rule when dissolving substances in a solution?

Answer 28

Like dissolves like.

Question 29

What does miscibility mean?

Answer 29

The ability of liquids to mix in all proportions, forming a solution.

Question 30

Give examples of common polar and non-polar mixes.

Answer 30

Oil and water = non-polar (don’t mix)

Water and ethanol (alcohol) = polar (do mix)