M2 - Chemical Bonding (1)

Question 1

State what is meant by the term ionic bond [1].

Answer 1

Electrostatic attraction between positive and negative ions ✔

*Ionic bonding occurs between a metal and non-metal *

Question 2

Describe what is meant by the term ionic lattice, in terms of the type and arrangement of particles present [2].

Answer 2

Repeating pattern ✔
of oppositely charged ions ✔

Question 3

What is the result of ions attracting oppositely charged ions in all directions?

Answer 3

Giant ionic lattice (e.g. NaCl)

Question 4

What happens to the melting / boiling points for giant ionic lattices, when the ionic charges increase in NaCl to MgO?

Answer 4

Melting / boling point increases as there is a stronger attraction between ions of Mg²⁺ and O^2- than Na⁺ and Cl^-

Question 5

Are ionic compounds soluble?

Answer 5

Yes, they dissolve in polar solvents such as water / Alcohols

Question 6

Can ionic compounds conduct electricity in solid, liquid or aqueous states, explain why

Answer 6

Na₂O conducts electricity when molten or in aq solution and not when solid ✔
Molten Na₂O has ions which are mobile ✔
Solid Na₂O has ions which are fixed (in position) OR ions are not mobile ✔

Question 7

Summarise the properties of most ionic compounds

Answer 7

High melting and boiling points.
Dissolve in polar solvents such as water.
Conduct electricity only when molten or dissolved in aqueous solution.

Question 8

Draw a ‘dot-and-cross’ diagram to show the bonding in solid barium chloride. Show outer electrons only [2].

Answer 8

Question 9

Draw a ‘dot-and-cross’ diagram to show the bonding in sodium sulfide. Show outer electrons only [2].

Answer 9

Question 10

Draw a ‘dot-and-cross’ diagram to show the bonding in MgBr₂. Show outer electrons only [2].

Answer 10

Question 11

What is meant by the term covalent bond [1].

Answer 11

Shared pair of electrons ✓

Covalent bonding occurs between non-metals

Question 12

What is a dative covalent bond? Provide an example of a compound that has a dative covalent bond

Answer 12

The shared pair of electrons has been supplied by one of the bonding atoms only.

The N atom on the ammonia molecule (NH₃) donates its lone pair of electrons to an H⁺ ion forming an ammonium ion, NH₄⁺.

Question 13

What is a multiple covalent bond? Provide some examples

Answer 13

Two atoms share more than one pair of electrons:

Question 14

Draw a ‘dot-and-cross’ diagram to show the bonding in a nitrogen molecule. Show outer electrons only [1].

Answer 14

Question 15

Na₂CO₃ contains the carbonate ion, CO₃²⁻, shown below.

Draw the ‘dot-and-cross’ diagram for the carbonate ion.

Show outer electrons only and use different symbols for electrons from C and O, and any ‘extra’ electrons [2].

Answer 15

Question 16

The displayed formula of a phosgene molecule is shown below.

Draw a ‘dot-and-cross’ diagram of a phosgene molecule, COCl₂.

Show outer electrons only [1].

Answer 16

Question 17

Define the term average bond enthalpy (ABE)?

Answer 17

The energy needed to break one mole of bonds in the gaseous state (kJ mol^-1)

Larger the ABE value, the stronger the covalent bond

Question 18

Describe the bonding and structure in graphite.

Explain why graphite is a good conductor, a soft material and has a very high melting point [5].

Answer 18

Giant covalent lattice
Arranged in layers
Good conductor - mobile electrons
High melting point - covalent bonds have to be broken
Soft - weak forces between the layers

Question 19

State what is meant by the term metallic bonding? [2]

Answer 19

Electrostatic attraction between delocalised electrons and the positive ions

Question 20

The melting points of the Period 3 metals sodium and magnesium are shown below.

Explain the differences in the melting points of sodium and magnesium, using the model of metallic bonding [3].

Answer 20

Magnesium has more outer OR bonding electrons ✓

Magnesium ions have a greater (positive) charge (density) ✓

Magnesium has a greater attraction between ions and delocalised electrons ✓

Question 21

Magnesium has metallic bonding and is a good conductor of electricity.

Describe, with the aid of a labelled diagram, the metallic bonding in magnesium and explain why magnesium conducts electricity.

Include the correct charges on the particles in your diagram [3].

Answer 21

Diagram with regular arrangement of labelled ‘Mg²⁺ ions’ OR ‘2+ ions’
AND attempt to show electrons ✓

Labelled electrons between other species AND statement anywhere of delocalised electrons (can be in text or in diagram) ✓

Electrons move ✓

Question 22

On a mini-white board / scrap piece of paper draw out the bond angles table, with the headings: number & type of electron pairs, electron-pair repulsion theory, shape, bond angle/^o & name

Answer 22

Question 23

What does molecular shape depend on?

Answer 23

Electron pairs around the central atom: bonded and lone pairs of electrons

Question 24

In what way do electron pairs interact?

Answer 24

They repel each other

Question 25

Which type of pair repels the most?

Answer 25

Lone pairs

Question 26

What is the name of the way to predict a molecule’s shape?

Answer 26

Electron pair repulsion theory

Question 27

Predict the shape and bond angle in a molecule that has 2 bonding pairs and 2 lone pairs around a central atom.

A Linear, 180°
B Non-linear, 104.5°
C Tetrahedral, 109.5°
D Trigonal planar, 120° [1]

Answer 27

Answer: B

Question 28

Predict the bond angle in an F₂O molecule and explain using the electron pair repulsioin theory [3].

Answer 28

Non-linear: 104.5 ✓
There are 2 bonded pairs and 2 lone pairs ✓
Lone pairs repel more than bonded pairs ✓

Question 29

Name the shape of the ammonia molecule (NH₃) and why ammonia has this shape and a bond angle of 107° [3]

Answer 29

Pyramidal ✓
There are 3 bonded pairs and 1 lone pair ✓
Lone pairs repel more than bonded pairs ✓

Question 30

Why does a water molecule have a different shape to a carbon dioxide molecule? [2]

Answer 30

Electron pairs repel and get as far apart as possible
Oxygen in H₂O has 2 bonded pairs and 2 lone pairs
Carbon in CO₂ has 2 bonded pairs (2 double bonds)

Question 31

What do dotted wedges, solid wedges and filled wedges stand for?

Answer 31

Question 32

Why does ammonium chloride not conduct electricity when solid but does when dissolved in water? [1]

Answer 32

Ions cannot move in a solid

Ions can move in solution

Question 33

What shape name and bond angle is given to a molecule with three bonded pairs & one lone pair?

Answer 33

Pyramidal & 107^o

Question 34

What shape name and bond angle is given to a molecule with two bonded pairs and two lone pairs?

Answer 34

Non-linear & 104.5^o

Question 35

What shape name and bond angle is given to a molecule with 2 bonded pairs around the central atom?

Answer 35

Linear & 180^o

Question 36

What shape name and bond angle is given to a molecule with 3 electron pairs and no lone pairs around the central atom?

Answer 36

Trigonal planar & 120^o

Question 37

What shape name and bond angle is given to a molecule with no lone pairs but four bonded pais?

Answer 37

Tetrahedral & 109.5^o

Question 38

What shape name and bond angle is given to a molecule with 6 electron pairs and no lone pairs around the central atom?

Answer 38

Octahedral & 90^o

Question 39

i. Predict the different shapes of, and bond angles in, NF₃ and BF₃ molecules [2].

ii. Explain why NF₃ and BF₃ molecules have different shapes and bond angles [2].

Answer 39

NF₃ has 3 bonded pairs AND 1 lone pair (of electrons) AND lone pairs repel more (than bonded pairs) ✓

BF₃ has three bonded pairs (of electrons) ✓

Question 40

State the shape of, and F—S—F bond angle in, an SF₆ molecule [2].

Answer 40

Octahedral ✓

90° ✓

Question 41

Complete Table 6.1 to predict bond angles a and b and name the shapes which makes these bond angles in the functional groups of carboxylic acids and sulfonic acids [2].

Answer 41