Bonding and Structure

Question 1

Define a Covalent Bond

Answer 1

A covalent bond is an electrostatic force between a shared paired of negative electrons and the positive nuclei of two atoms

Question 2

Compare and contrast these two different types of bonds

Answer 2

• Both include two orbitals overlapping
• Sigma involves s and p whilst Pi involves p orbitals only
• Sigma overlaps two lobes whilst pi overlaps 4 lobes

Question 3

Define ‘Electronegativity’

Answer 3

Electronegativity is a measure of a tendency of an atom to attract a bonding pair of electrons in a covalent bond

Question 4

Explain the factor affecting electronegativity

Answer 4

• Nuclear Charge
  -Atomic radius

Question 5

Give the electronegativity difference ranges for different types of bonds

Answer 5

Non-polar covalent bond <0.4
Polar Covalent bond 0.4 - 1.7
Ionic bond > 1.7

Question 6

Explain why a molecule can contain polar bonds but be non polar

Answer 6

• The shape of the molecule and where the polar bonds are whether the positive and negative dipoles coincide
• If the shape is symmetrical and the polar bonds cancel out as they coincide

Question 7

Define an Ionic Bond

Answer 7

Ionic Bonding is the Electrostatic attraction between oppositely charged positive and negatively charged ions.

Question 8

Describe an ionic compound and its properties

Answer 8

• Ionic lattice structure held together by electrostatic forces by oppositely charged ions for the maximum number of attraction
• High melting and boiling points due to strong electrostatic forces
• Brittle due to layers being able to be distorted
• Ions move when dissolved in a solution

Question 9

Explain the bond lengths between C-C and C=C

Answer 9

C=C is shorter
C=C has a higher electron density
This leads to greater attraction between positive nuclei and negative electron
Therefore C=C has a greater bond strength

Question 10

State the 2 factors affecting the strength of an ionic bond

Answer 10

• The greater the charge the stronger the ionic bond
• The smaller the ionic radius, the stronger the ionic bond

Question 11

Define isoelectronic elements and its factor affecting its ionic radius

Answer 11

• a group of elements that have an identical electron configuration
• more protons result in a greater nuclear charge reducing ion radius

Question 12

Describe the Valence Shell Electron Pair Repulsion Theory

Answer 12

Electrons pairs are negative and repel each other
They will space themselves out from one another to maximise separation and minimise repulsion
The basic shape of a molecule is the number of electrons around an central atom

Question 13

State the shape and the bonding angle for 2 election bonding pairs

Answer 13

Linear
180°

Question 14

State the shape and the bonding angle for 3 election bonding pairs

Answer 14

Trigonal Planar
120°

Question 15

State the shape and the bonding angle for 4 electron bonding pairs

Answer 15

Tetrahedral
109.5°

Question 16

State the shape and the bonding angle for 5 election bonding pairs

Answer 16

Trigonal Bipyramidal
120°, 90°, 180°

Question 17

State the shape and the bonding angle for 6 election bonding pairs

Answer 17

Octahedral
90°, 180°

Question 18

Describe the affect of lone pairs on its shape

Answer 18

Lone pairs cause greater repulsion and will push bonding pairs closer together, reducing bond angle by 2.5°

Question 19

State the three type of intermolecular bonding

Answer 19

• London forces (instantaneous dipole- induced dipole)
• Permanent Dipole
• Hydrogen bonding

Question 20

Describe the conditions for hydrogen bonding

Answer 20

• A delta positive hydrogen atom bonded to a small highly electronegative atom(O,F,N)
• Another highly electronegative atom on a separate molecule which has a lone pair

Question 21

Explain the properties of H20, NH3 and HF

Answer 21

The anomalously high boiling points of H2O, NH3 and HF are caused by the hydrogen bonding between these molecules in addition to their London forces. The additional forces require more energy to break and so have higher boiling points

Question 22

Explain why water has a relatively high boiling and temperature

Answer 22

• Presence of hydrogen bonds which require additional energy to break
• Water has 2 lone pairs on the oxygen atom which can form 2 hydrogen bonds
• Each water molecule can form up to 4 hydrogen bonds(oxygen - 2, each hydrogen - 1)
• Also the addition of dipole - dipole forces

Question 23

Explain why ice has a lower density in its liquid form

Answer 23

When the hydrogen bonds are broken as the ice melts, the water molecules get closer together. That means that ice is less dense than water, and so will float on the water.

Question 24

Describe the trend in alkane when the chain length increases

Answer 24

• Boiling temperature increases
• More electrons present
• Greater London forces (inducing dipole)

Question 25

Describe the effect of branching on alkanes

Answer 25

• Lower boiling temperature
• Reduced surface Area contact with other molecules
• Lowers London forces

Question 26

Explain why alcohols have a higher boiling point than alkanes with the similar number of electrons

Answer 26

• Presence of hydrogen bonding on oxygen atom in addition to London forces
• Alkanes have London forces only

Question 27

Describe the trend of hydrogen halides

Answer 27

• HF forms hydrogen bonds whilst other form dipole-dipole or London forces
• Thisresults in a slight jump in energy between HF and HCl
  -After Cl it increases due to London forces getting stronger and greater permanent dipole forces

Question 28

Explain why water can dissolve some ionic compounds

Answer 28

The ionic bonds between cation and anion are broken.
Ion-dipole forces between oxygen and cation and hydrogen and anion are formed.

Question 29

Explain if water can dissolve simple alcohols

Answer 29

• Water and simple alcohols can form hydrogen bond with each other
  -The oxygen atom on ethanol has a lone pair which is available for a hydrogen bond

Question 30

Explain if water can dissolve polar molecules like halogenoalkanes

Answer 30

• Water cannot form hydrogen bonds with halogenoalkanes
• Halogenoalkanes can only form dipole-dipole interactions
• Forming two immiscible(seperate) layers

Question 31

Describe the two conditions for dissolving compounds

Answer 31

• The solute must separate from one another, and become surrounded by solvent particles
• The forces of attraction between the solvent and solute particles must be sufficiently strong to overcome the solvent-solvent and solute-solute forces

Question 32

Define ‘Metallic Bonding’

Answer 32

The electrostatic attraction between delocalised electrons and metal ions.

Question 33

State two simple covalent structures

Answer 33

• Iodine(I2)
• Water(H20)

Question 34

State three places where giant lattice locations are found

Answer 34

• Ionic Solids(giant ionic lattices)
• Giant Covalent (diamond, silicon dioxide, graphite and graphene)
• Metal solids(giant metallic lattices)

Question 35

Describe the properties and uses of Diamond

Answer 35

4 strong covalent bonds
Very Hard - Abrasives, Drills
High melting and boiling point - conducts thermal energy very well
Refracts light - Jewellery

Question 36

Describe the properties and uses of Buckminster Fullerene

Answer 36

Roughly spherical with each carbon atom bonded to nearest 3 atoms
Very Soluble - mascara and printing ink
Delocalised electrons - Good insulators
Weak intermolecular forces - drug delivery

Question 37

Describe the properties and uses of Graphite

Answer 37

Hexagonal arrangement in each layer, arranged in layers, each carbon bonded to 3 others
Delocalised electrons conducting electricity - Electrodes
Strong covalent bonds creating good tensile strength- Composites

Question 38

Describe the properties and uses of Graphene

Answer 38

Singular hexangular layer of carbon boned to 3 atoms
Delocalised Electrons - good conductors
Lightweight and strong - Aircrafts or cars
Transparent, flexible, conductive - Touchscreens