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Edexcel A-Level Chemistry > Topic 2 - STRUCTURE AND BONDING > Flashcards

Topic 2 - STRUCTURE AND BONDING Flashcards

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1
Q

What are the 3 types of chemical bond?

A
  • Ionic
  • Covalent
  • Metallic
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2
Q

What are the 4 types of structure?

A
  • Simple molecular
  • Giant covalent lattice
  • Giant ionic lattice
  • Giant metallic lattice
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3
Q

What is the definition of a metal?

A

Something that forms positive ions

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4
Q

What is the definition of ionic bonding?

A

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

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5
Q

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

A

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

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6
Q

Why does NaF have a high melting point?

A
  • Giant ionic lattice structure
  • Many strong electrostatic forces in all directions]
  • Which require lots of energy to break
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7
Q

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

A
  • 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
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8
Q

Why can’t solid ionic substances conduct electricity?

A

The ions are in fixed positions, hence cannot move

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9
Q

In what form can ionic substances conduct electricity?

A

Molten/aqueous ionic substances
- Ions are free to move

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10
Q

What is the definition of metallic bonding?

A

The electrostatic attraction between positively charged metal ions and delocalised electrons

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11
Q

Why do metallic substances have high melting points?

A

A large amount of energy is required to separate the particles

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12
Q

Why are metallic substances insoluble in water?

A

There are no interactions with the water molecules

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13
Q

What is the definition of covalent bonding?

A

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

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14
Q

What are lone pairs?

A

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

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15
Q

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

A
  • 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)
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16
Q

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

A

18

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17
Q

What is the definition of double covalent bonds?

A

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

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18
Q

What is the definition of triple covalent bonds?

A

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

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19
Q

What is the definition of dative bonding?

A

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

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20
Q

Give an example of dative bonding

A

Boron trifluoride

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21
Q

Why is X-ray diffraction useful?

A

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

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22
Q

How is covalent bond strength determined by average bond enthalpy?

A
  • 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
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23
Q

What substances have monoatomic structures?

A
  • Group 8 elements
  • Made of atoms
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24
Q

What substances have simple molecular structures?

A
  • Most non-metal elements (except group 8)
  • Most non-metal compounds
    (- Molecules)
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25
Q

What substances have giant covalent structures?

A
  • Diamond
  • Graphite
  • Silicon dioxide
    (- Atoms)
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26
Q

What substances have ionic structures?

A

Substances containing both metals and non metals
(- Ions)

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27
Q

What substances have metallic structures?

A

Metals
(- Ions and delocalised electrons)

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28
Q

What does a solid line represent in 3D drawings?

A

A bond in the plane of the paper

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29
Q

What does a solid wedge represent in 3D drawings?

A

Something coming out of the plane of the paper

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30
Q

What does a dotted wedge represent in 3D drawings?

A

Something going into the plane of the paper

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31
Q

Give the:
- Name of the shape
- Bond angle

Of a molecule with 2 electron pairs

A
  • Linear/planar
  • 180degrees
32
Q

Give the:
- Name of the shape
- Bond angle

Of a molecule with 3 electron pairs

A
  • Trigonal planar
  • 120degrees
33
Q

Give the:
- Name of the shape
- Bond angle

Of a molecule with 4 electron pairs

A
  • Tetrahedral
  • 109.5degrees
34
Q

Give the:
- Name of the shape
- Bond angle

Of a molecule with 5 electron pairs

A
  • Trigonal bipyramidal
  • 120 + 90 degrees
35
Q

Give the:
- Name of the shape
- Bond angle

Of a molecule with 6 electron pairs

A
  • Octahedral
  • 90degrees
36
Q

Why are molecules shaped the way they are?

A
  • The electron pairs try to repel each other as far as possible
  • Hence the molecule is very stable
37
Q

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

A

For every lone pair, bond angles reduce by 2.5degrees

38
Q

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

A

Linear

39
Q

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

A

Trigonal planar

40
Q

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

A

Bent (V-shaped)

41
Q

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

A

Tetrahedral

42
Q

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

A

Trigonal pyramidal

43
Q

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

A

Bent (V-shaped)

44
Q

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

A

Trigonal bipyramidal

45
Q

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

A

Trigonal pyramidal or see-saw

46
Q

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

A

Trigonal planar or T-shape

47
Q

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

A

Octahedral

48
Q

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

A

Square pyramid

49
Q

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

A

Square planar

50
Q

Steps for working out the shape of molecules

A
  • Number of valence electrons on central atom
  • Number of atoms bonded to central atom
  • Number of lone pairs
  • Bonding pairs + lone pairs
51
Q

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

A
  • 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
52
Q

What is the definition of electronegativity?

A

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

53
Q

Which element has the highest electronegativity?

A

Fluorine

54
Q

Why does electronegativity increase along a period?

A
  • More protons
  • Nuclear charge is greater
55
Q

Why does electronegativity decrease down a group?

A
  • Bonded electrons are more shielded
56
Q

How does magnitude affect ability to polarise ions?

A
  • Bigger the magnitude of charge the more easily it can polarise ions
  • The bigger the ion the more easily it can polarise ions
57
Q

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

A

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

58
Q

What are polar bonds?

A

When there is an uneven distribution of the bonded electrons

59
Q

How can you work out if a molecule is symmetrical?

A
  • All the atoms around the central atom are the same
  • There are no lone pairs on the central atom
60
Q

How can you tell if a molecule in unsymmetrical?

A
  • The central atoms has two or more different atoms
    OR
  • The central atom has one or more lone pairs
61
Q

What are the 3 types of intermolecular force?

A
  • Hydrogen bonding
  • Permanent dipole-dipole forces
  • London forces
62
Q

What are London forces?

A
  • Type of intermolecular force
  • Temporary, induced dipole-dipole force
  • Occur between non-polar molecules
63
Q

Why do London forces occur?

A
  • The electrons are constantly moving around
  • There will be an uneven electron distribution at any time
64
Q

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

A
  • The number of electrons in the molecule or an atom increases
  • The surface contact of the molecules increases
65
Q

Where do permanent dipole-dipole interactions occur?

A

Between polar molecules

66
Q

What is the definition of hydrogen bonding?

A

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

67
Q

What are the properties of molecular substances?

A
  • 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
68
Q

Describe the properties of graphite

A
  • 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
69
Q

Describe the properties of diamond

A
  • Allotrope of carbon
  • Each C atom is covalently bonded to 4 other C atoms
  • Tetrahedral arrangement
  • Insoluble in water: No interactions
70
Q

Describe the arrangement and motion of particles in a solid

A
  • Regular and tightly packed
  • No movement of particles from place to place, particles only vibrate
71
Q

Describe the arrangement and motion of particles in a liquid

A
  • Random and close
  • Particles can move past/over each other
72
Q

Describe the arrangement and motion of particles in a gas

A
  • Random and far apart
  • Particles move rapidly from place to place
73
Q

Why does water have a higher melting point than expected?

A

It has hydrogen bonds which are very strong forces between molecules

74
Q

Why is solid water less dense than the liquid?

A

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

75
Q

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

A

Hydrogen bonding

76
Q

How do we test for polar molecules?

A

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

Edexcel A-Level Chemistry (16 decks)

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