Topic 2 - STRUCTURE AND BONDING

Question 1

What are the 3 types of chemical bond?

Answer 1

• Ionic
• Covalent
• Metallic

Question 2

What are the 4 types of structure?

Answer 2

• Simple molecular
• Giant covalent lattice
• Giant ionic lattice
• Giant metallic lattice

Question 3

What is the definition of a metal?

Answer 3

Something that forms positive ions

Question 4

What is the definition of ionic bonding?

Answer 4

The electrostatic attraction between oppositely charged ions in all directions (metal/non metal)

Question 5

What affects the strength of the electrostatic forces in ionic compounds?

Answer 5

The electrostatic forces will be stronger when:
- The ion is smaller
- The magnitude of charge is greater

Question 6

Why does NaF have a high melting point?

Answer 6

• Giant ionic lattice structure
• Many strong electrostatic forces in all directions]
• Which require lots of energy to break

Question 7

Would you expect CaF2 or NaF to have a higher melting point? Why?

Answer 7

• Ca 2+ has a higher magnitude of charge but a bigger ionic radius
• Na + has a smaller charge and a smaller ionic radius
• Hence CaF2 has a higher melting point

Question 8

Why can’t solid ionic substances conduct electricity?

Answer 8

The ions are in fixed positions, hence cannot move

Question 9

In what form can ionic substances conduct electricity?

Answer 9

Molten/aqueous ionic substances
- Ions are free to move

Question 10

What is the definition of metallic bonding?

Answer 10

The electrostatic attraction between positively charged metal ions and delocalised electrons

Question 11

Why do metallic substances have high melting points?

Answer 11

A large amount of energy is required to separate the particles

Question 12

Why are metallic substances insoluble in water?

Answer 12

There are no interactions with the water molecules

Question 13

What is the definition of covalent bonding?

Answer 13

The electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 14

What are lone pairs?

Answer 14

Electron pairs that aren’t shared
- ie. electrons that are not involved in a bond

Question 15

What is the octet rule, and why is it sometimes broken?

Answer 15

• 8 outer electrons is the most stable configuration
• However, sometimes the atom has less than 4 electrons to share
• Eg BF3 (Boron only has 3 electrons to share)

Question 16

How many electrons do sulphur, chlorine and phosphorous all have the ability to accommodate in their valence shell?

Answer 16

18

Question 17

What is the definition of double covalent bonds?

Answer 17

The electrostatic attraction between 2 shared pairs of electrons and the nuclei of the bonded atoms

Question 18

What is the definition of triple covalent bonds?

Answer 18

The electrostatic attraction between 3 pairs of electrons and the nuclei of the the bonded atoms

Question 19

What is the definition of dative bonding?

Answer 19

A dative bond is a covalent bond where only one of the bonded atoms donates both electrons being shared

Question 20

Give an example of dative bonding

Answer 20

Boron trifluoride

Question 21

Why is X-ray diffraction useful?

Answer 21

It allows bond lengths and spacing between ions or structures of crystals to be investigated

Question 22

How is covalent bond strength determined by average bond enthalpy?

Answer 22

• Single bonds are longer than double bonds, which are longer than triple bonds
• Large atoms form longer bonds as bonding pair of electrons is more shielded from the nucleus
• Shorter the bond, the stronger the bond enthalpy

Question 23

What substances have monoatomic structures?

Answer 23

• Group 8 elements
• Made of atoms

Question 24

What substances have simple molecular structures?

Answer 24

• Most non-metal elements (except group 8)
• Most non-metal compounds
  (- Molecules)

Question 25

What substances have giant covalent structures?

Answer 25

- Diamond - Graphite - Silicon dioxide (- Atoms)

Question 26

What substances have ionic structures?

Answer 26

Substances containing both metals and non metals (- Ions)

Question 27

What substances have metallic structures?

Answer 27

Metals (- Ions and delocalised electrons)

Question 28

What does a solid line represent in 3D drawings?

Answer 28

A bond in the plane of the paper

Question 29

What does a solid wedge represent in 3D drawings?

Answer 29

Something coming out of the plane of the paper

Question 30

What does a dotted wedge represent in 3D drawings?

Answer 30

Something going into the plane of the paper

Question 31

Give the: - Name of the shape - Bond angle Of a molecule with 2 electron pairs

Answer 31

- Linear/planar - 180degrees

Question 32

Give the: - Name of the shape - Bond angle Of a molecule with 3 electron pairs

Answer 32

- Trigonal planar - 120degrees

Question 33

Give the: - Name of the shape - Bond angle Of a molecule with 4 electron pairs

Answer 33

- Tetrahedral - 109.5degrees

Question 34

Give the: - Name of the shape - Bond angle Of a molecule with 5 electron pairs

Answer 34

- Trigonal bipyramidal - 120 + 90 degrees

Question 35

Give the: - Name of the shape - Bond angle Of a molecule with 6 electron pairs

Answer 35

- Octahedral - 90degrees

Question 36

Why are molecules shaped the way they are?

Answer 36

- The electron pairs try to repel each other as far as possible - Hence the molecule is very stable

Question 37

How does every extra lone pair around an atom affect bond angles?

Answer 37

For every lone pair, bond angles reduce by 2.5degrees

Question 38

What is the shape produced when there are: - 2 bonding pairs - 0 lone pairs?

Answer 38

Linear

Question 39

What is the shape produced when there are: - 3 bonding pairs - 0 lone pairs?

Answer 39

Trigonal planar

Question 40

What is the shape produced when there are: - 2 bonding pairs - 1 lone pairs?

Answer 40

Bent (V-shaped)

Question 41

What is the shape produced when there are: - 4 bonding pairs - 0 lone pairs?

Answer 41

Tetrahedral

Question 42

What is the shape produced when there are: - 3 bonding pairs - 1 lone pairs?

Answer 42

Trigonal pyramidal

Question 43

What is the shape produced when there are: - 2 bonding pairs - 2 lone pairs?

Answer 43

Bent (V-shaped)

Question 44

What is the shape produced when there are: - 5 bonding pairs - 0 lone pairs?

Answer 44

Trigonal bipyramidal

Question 45

What is the shape produced when there are: - 4 bonding pairs - 1 lone pairs?

Answer 45

Trigonal pyramidal or see-saw

Question 46

What is the shape produced when there are: - 3 bonding pairs - 2 lone pairs?

Answer 46

Trigonal planar or T-shape

Question 47

What is the shape produced when there are: - 6 bonding pairs - 0 lone pairs?

Answer 47

Octahedral

Question 48

What is the shape produced when there are: - 5 bonding pairs - 1 lone pairs?

Answer 48

Square pyramid

Question 49

What is the shape produced when there are: - 4 bonding pairs - 2 lone pairs?

Answer 49

Square planar

Question 50

Steps for working out the shape of molecules

Answer 50

- Number of valence electrons on central atom - Number of atoms bonded to central atom - Number of lone pairs - Bonding pairs + lone pairs

Question 51

Explain why the bond angle in water is less than the bond angle in ammonia (PPQ)

Answer 51

- Oxygen has 2 lone pairs of electrons but nitrogen only has one - So the repulsion from the oxygen lone pairs is greater, reducing bond angle

Question 52

What is the definition of electronegativity?

Answer 52

The relative ability of an atom to attract a pair of electrons in a covalent bond

Question 53

Which element has the highest electronegativity?

Answer 53

Fluorine

Question 54

Why does electronegativity increase along a period?

Answer 54

- More protons - Nuclear charge is greater

Question 55

Why does electronegativity decrease down a group?

Answer 55

- Bonded electrons are more shielded

Question 56

How does magnitude affect ability to polarise ions?

Answer 56

- Bigger the magnitude of charge the more easily it can polarise ions - The bigger the ion the more easily it can polarise ions

Question 57

What are non-polar bonds and when do they occur?

Answer 57

When the bonded electron pair is shared equally - Within an element - Between 2 elements with similar electronegativities

Question 58

What are polar bonds?

Answer 58

When there is an uneven distribution of the bonded electrons

Question 59

How can you work out if a molecule is symmetrical?

Answer 59

- All the atoms around the central atom are the same - There are no lone pairs on the central atom

Question 60

How can you tell if a molecule in unsymmetrical?

Answer 60

- The central atoms has two or more different atoms OR - The central atom has one or more lone pairs

Question 61

What are the 3 types of intermolecular force?

Answer 61

- Hydrogen bonding - Permanent dipole-dipole forces - London forces

Question 62

What are London forces?

Answer 62

- Type of intermolecular force - Temporary, induced dipole-dipole force - Occur between non-polar molecules

Question 63

Why do London forces occur?

Answer 63

- The electrons are constantly moving around - There will be an uneven electron distribution at any time

Question 64

London forces are very weak; However, they strengthen when?

Answer 64

- The number of electrons in the molecule or an atom increases - The surface contact of the molecules increases

Question 65

Where do permanent dipole-dipole interactions occur?

Answer 65

Between polar molecules

Question 66

What is the definition of hydrogen bonding?

Answer 66

The interaction between the lone pair of electrons on a nitrogen, oxygen or fluorine atom and a hydrogen atom which is bonded to an N,O or F atom

Question 67

What are the properties of molecular substances?

Answer 67

- Low mp/bp: Little energy required to overcome IM forces - Neutral: Cannot carry charge - Polar molecules dissolve in polar solvents: PD-PD interactions form - Non-polar molecules dissolve in non-polar solvents: London forces can form between the solvent and solute

Question 68

Describe the properties of graphite

Answer 68

- Allotrope of carbon - Each C atom is covalently bonded to 3 other C atoms - Hexagonal arrangement - Remaining electron is delocalised between layers - Insoluble in water: No interactions

Question 69

Describe the properties of diamond

Answer 69

- Allotrope of carbon - Each C atom is covalently bonded to 4 other C atoms - Tetrahedral arrangement - Insoluble in water: No interactions

Question 70

Describe the arrangement and motion of particles in a solid

Answer 70

- Regular and tightly packed - No movement of particles from place to place, particles only vibrate

Question 71

Describe the arrangement and motion of particles in a liquid

Answer 71

- Random and close - Particles can move past/over each other

Question 72

Describe the arrangement and motion of particles in a gas

Answer 72

- Random and far apart - Particles move rapidly from place to place

Question 73

Why does water have a higher melting point than expected?

Answer 73

It has hydrogen bonds which are very strong forces between molecules

Question 74

Why is solid water less dense than the liquid?

Answer 74

In a solid, it forms an open lattice which is less dense than liquid water

Question 75

What is the common cause of the anomalous properties of water?

Answer 75

Hydrogen bonding

Question 76

How do we test for polar molecules?

Answer 76

Diverting streams method: - Use a burette to create a stream of the liquid you are testing - Charge a plastic rod - If the liquid is polar the stream will be deflected