Chemical Bonding

Question 1

Electronegativity

Answer 1

A measure of the tendency of an atom to attract a bonding pair of electrons.

Question 2

What is an Intramolecular Bond?

Answer 2

A bond between atoms within molecules.

Question 3

What indicates a covalent bond?

Answer 3

A sharing of at least one pair of electrons by two atoms.

Question 4

When is a covalent bond polar?

Answer 4

When electrons are unequally shared due to a difference in electronegativity.

Question 5

When is a covalent bond non-polar?

Answer 5

When the electrons are equally shared due to zero difference in electronegativity.

Question 6

What determines the polarity value of a bond?

Answer 6

Electronegativity.
The greater the difference in electronegativity the more polar the bond.

Question 7

What indicates ionic bonding?

Answer 7

A transfer of electrons to form cations and anions which are electrostatically attracted in an ionic crystal lattice.

Question 8

Between what type of atoms do ionic bonds occur?

Answer 8

Metals (cations) and non-metals (anions).

Question 9

Between what type of atoms do covalent bonds occur?

Answer 9

Non-metals.

Question 10

Between what type of atoms do metallic bonds occur?

Answer 10

Metals.

Question 11

What indicates metallic bonding?

Answer 11

The attraction between positive kernels and a sea of delocalised electrons.

Question 12

What is an Intermolecular Force?

Answer 12

A force of attraction between molecules or between atoms of noble gases.

Question 13

What is a polar molecule (dipole)?

Answer 13

A molecule in which the electrons are unevenly distributed resulting in a S+ and S- end.

Question 14

Name a specific intermolecular force.

Answer 14

van der Walls forces.

Question 15

What do all interactions between molecules involve?

Answer 15

London forces.

Question 16

What do metals and graphite do and why?

Answer 16

Metals and graphite conduct electricity due to the presence of delocalised valence electrons.

Question 17

Do ionic compounds conduct electricity? If so, when?

Answer 17

Yes.
Ionic compounds only conduct electricity when molten or in aqueous solution, i.e. when the ions are free.

When a potential difference is applied, it is these electrons or ions that move, resulting in a current.

Question 18

What are the bonds between polar molecules called?

Answer 18

Hydrogen Bonds.

Question 19

How is hydrogen bonded?

Answer 19

Hydrogen is covalently bonded to either N, O or F.

Question 20

Why does hydrogen only bond to Nitrogen (N), Oxygen (O) or Fluorine (F)?

Answer 20

Due to these being:
- small atoms
- of high electronegativity
- with at least one lone pair of electrons

Question 21

Discuss the relationship between electronegativity and polarity.

Answer 21

The greater the difference in electronegativity the more polar the bond.

Question 22

Name the different types of van Der Waals forces.

Answer 22

• London forces (induced dipole forces or dispersion forces)
• Dipole-dipole forces
• Hydrogen bonding as a special case of dipole-dipole forces

Question 23

What influences the strength of London Forces?

Answer 23

The size of the temporary dipoles.

Question 24

What influences the size of the temporary dipoles?

Answer 24

• The number of electrons.
• the interacting surface of the molecule (e.g. Long unbranched chain vs branched chain)

Question 25

Why are hydrogen bonds stronger than dipoles-dipole forces?

Answer 25

Due to:
- the high polarity of the covalent bond formed between hydrogen and either N,O or F
- the fact that the molecules can get close together

Question 26

Why are hydrogen bonds stronger than dipoles-dipole forces?

Answer 26

Due to:
- the high polarity of the covalent bond formed between hydrogen and either N,O or F
- the fact that the molecules can get close together

Question 27

Why are melting points high in giant structures such as diamond, graphite and silicon dioxide?

Answer 27

Due to the large amount of energy needed to break the many strong covalent bonds.

Question 28

How is the melting point determined in giant ionic solids (e.g. sodium chloride)?

Answer 28

By the strength of the many electrostatic forces of attraction (ionic bonds) between the cations and the anions in the ionic crystal lattice.

Question 29

How are the melting and boiling points affected in simple molecular substances?

Answer 29

By the strength and the relative number per molecule ( for hydrogen bonds) of the intermolecular forces.

Question 30

What is the difference when comparing the melting and boiling points of molecular substances in the same group on the Periodic Table or the same homologous series?

Answer 30

The difference is mainly due to the London Forces, the exception being those that experience hydrogen bonds.

Question 31

What is the difference when comparing the melting and boiling points of molecular substances of similar mass in different groups on the Periodic Table or different homologous series?

Answer 31

The difference is due to the presence of other intermolecular forces (dipoles-dipole and/or hydrogen bonds) besides the London Forces which are present between all molecules.

Question 32

What is the difference when comparing the melting and boiling points of molecular substances that involve hydrogen bonding?

Answer 32

The difference is due to the relative number of hydrogen bonds per molecules that occur between the molecules.

E.g. on average H2O forms more H-bonds per molecule than NH3 and HF)