2A: Bonding

Question 1

What is ionic bonding?

Answer 1

The strong electrostatic attraction between oppositely charged ions

Question 2

How do ionic radius and ionic charge affect the strength of ionic bonding?

Answer 2

• Smaller ionic radius and greater ionic charge
• So greater charge density
• So stronger ionic bonding

Question 3

Describe the formation of ions in terms of electron loss or gain.

Answer 3

Loss of electrons forms positive ions.

Gain of electrons forms negative ions.

Question 4

Explain the trend in ionic radius down a group.

Answer 4

Ionic radius increases, because more electron shells.

Question 5

Explain the trend in ionic radius for isoelectronic ions.

Answer 5

Ions with a higher nuclear charge have a smaller ionic radius.

Question 6

Describe the experiment to show the migration of ions.

Answer 6

Ionic compound on damp filter paper with oppositely charged electrodes.
The opposite ions migrate towards the electrodes.

Proves the existence of ions.

Question 7

What is covalent bonding

Answer 7

The strong electrostatic attraction between two nuclei and the shared pair of electrons between them

Question 8

Explain the relationship between bond lengths and bond strengths for covalent bonds?

Answer 8

Shorter bond = stronger bond,
because electrons are closer to the nucleus

Question 9

State and explain the trend in X-X bond length as you go down group 7.

Answer 9

More electron shells,
so more shielding,
so weaker attraction between the nuclei and the bonding electrons,
so longer bond.

Question 10

What determines the shape of a simple molecule or ion?

Answer 10

The repulsion between the electron pairs that surround a central atom.
Electron pairs will take a position where repulsion is minimised.

Question 11

Shape and bond angles of BeCl₂

Answer 11

Linear
180

Question 12

Shape and bond angles of BCl₃

Answer 12

Trigonal planar
120

Question 13

Shape and bond angles of CH₄

Answer 13

Tetrahedral
109.5

Question 14

Shape and bond angles of NH₃

Answer 14

Trigonal Pyramidal
107

Question 15

Shape and bond angle of NH₄⁺

Answer 15

Tetrahedral
109.5

Question 16

Shape and bond angle of H₂O

Answer 16

Bent
104.5

Question 17

Shape and bond angles of PCl₅

Answer 17

Trigonal Bipyramidal
120 and 90

Question 18

Shape and bond angle of SF₆

Answer 18

Octahedral
90

Question 19

What is electronegativity?

Answer 19

The ability of an atom to attract the bonding electrons in a covalent bond

Question 20

How is a dipole formed?

Answer 20

When bonding atoms have a large difference in electronegativity, they attract electrons unequally, and one gets a slight positive charge and the other a slight negative charge.

Question 21

What is a polar molecule?

Answer 21

A molecule with polar bonds creating an overall dipole.

Question 22

How do you practically check if a substance contains polar molecules?

Answer 22

Electrostatic charge next to a jet of liquid.
Polar molecules will be attracted.

Question 23

Describe London Forces.

Answer 23

Instantaneous dipole - induced dipole.
Caused by an instantaneous imbalance of electrons in the molecule.
The resultant dipole induces a dipole in a nearby atom or molecule.

Strength increases with number of electrons.

Question 24

Describe permanent dipole attractions.

Answer 24

Two molecules with permanent overall dipoles.
Attraction between the positive charge in one molecule and the negative charge in the other.

Question 25

Describe a diagram to show hydrogen bonding.

Answer 25

Lone pair on the O, delta+ on H and delta- on O, dashed line between H and the lone pair

Question 26

What is needed for a Hydrogen Bond to form?

Answer 26

* A large dipole between a H atom and a highly electronegative atom (eg O, N or F) * A small H atom that can get very close to other molecules * A lone pair of electrons on the O, N or F atom that the positively charged H atom can line up with

Question 27

Explain the melting and boiling points of water.

Answer 27

Relatively high temperatures. Each molecule has 2 hydrogens connected to an oxygen, so it can form 2 hydrogen bonds with other water molecules.

Question 28

Explain the density of ice compared to water.

Answer 28

Lower density. As water freezes, the hydrogen bonds pull the water molecules into fixed positions in a comparatively open lattice.

Question 29

State and explain the trends in boiling temperatures of alkanes with increasing chain length.

Answer 29

As chain length increases, there are more electrons, so London forces are stronger, so boiling point increases.

Question 30

State and explain the effect of branching in the carbon chain on the boiling temperatures of alkanes

Answer 30

Molecules cannot get as close together, so London forces are weaker, so boiling point is decreased.

Question 31

State and explain the volatility of alcohols compared to alkanes with a similar number of electrons.

Answer 31

The -OH group causes hydrogen bonding, so boiling point is much higher than alkanes, so volatility is relatively low.

Question 32

State and explain the trends in boiling temperatures of the hydrogen halides, HF to HI.

Answer 32

HF has hydrogen bonding, so boiling point is highest. Down the group from HCl to HI, number of electrons increases so London forces are stronger, so boiling point increases.

Question 33

Explain why some ionic compounds dissolve in water.

Answer 33

The polar water molecules are attracted to the charged ions. The water molecules hydrate the ions and break the ionic bonds in the compound.

Question 34

Explain why simple alcohols dissolve in water.

Answer 34

Alcohols form hydrogen bonds between molecules. Alcohols also form hydrogen bonds with water molecules. Bonds formed are similar to bonds broken.

Question 35

Explain why polar molecules such as halogenoalkanes are insoluble in water.

Answer 35

They are unable to form hydrogen bonds with water.

Question 36

What compounds would you dissolve in non-aqueous solvents?

Answer 36

Compounds that have similar intermolecular forces to those in the solvent.

Question 37

What is metallic bonding?

Answer 37

The strong electrostatic attraction between metal ions and the delocalised electrons

Question 38

What colours would be observed after the electrolysis of copper(II) chromate(VI)?

Answer 38

Cathode: Blue (copper ions) Anode: Yellow (chromate ions)