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