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A-LEVEL CHEM > PHYSICAL CHEM - BONDING > Flashcards

PHYSICAL CHEM - BONDING Flashcards

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1
Q

What is ionic bonding?

A

transfer of electrons from a metal to a non-metal

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2
Q

What is the structure of an ionic compound?

A

giant ionic lattice

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3
Q

What forces are present in ionic compounds?

A

strong electrostatic forces of attraction between oppositely charged ions

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4
Q

What are the properties of ionic compounds?

A
  • high melting and boiling points
  • conduct when molten/in solution (but don’t conduct when solid)
  • soluble
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5
Q

Why do ionic compounds have high melting and boiling points?

A

strong electrostatic forces between oppositely charged ions require lots of energy to overcome

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6
Q

Why do ionic compounds conduct when molten/in solution but not when solid?

A
  • when solid, ions are not free to move
  • when molten/in solution, ions are free to move and can carry a charge through the structure
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7
Q

Why are ionic compounds soluble?

A
  • water molecules are polar
  • charged parts of water molecules pull ions away from the lattice causing the ionic compound to dissolve
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8
Q

What is covalent bonding?

A

sharing of electrons between 2 non-metals

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9
Q

What is the structure of a molecular compound?

A

a simple molecular structure

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10
Q

What forces are present in molecular compounds?

A
  • weak intermolecular forces between molecules (permanent dipole - dipole forces, van der waals forces, hydrogen bonding)
  • covalent bonds between atoms in a molecule (eg: I2)
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11
Q

What are the properties of a molecular compound?

A
  • low melting and boiling points
  • don’t conduct
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12
Q

Why do molecular compounds have low melting and boiling points?

A

weak intermolecular forces between molecules
require little energy to overcome

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13
Q

Why do molecular compounds not conduct?

A

no electrons free to move and carry a charge through the structure

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14
Q

What is diamond’s structure?

A
  • giant covalent structure
  • each carbon atom bonded to 4 others
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15
Q

What is graphite’s structure?

A
  • giant covalent structure
  • layers (graphene)
  • each carbon atom bonded to 3 others
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16
Q

What type of bonding occurs in diamond and graphite?

A

strong covalent bonds

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17
Q

What are diamond’s properties?

A
  • high melting and boiling points
  • strong/hard
  • doesn’t conduct
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18
Q

Why does diamond have high melting and boiling points?

A

strong covalent bonds require lots of energy to overcome

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19
Q

What makes diamond so strong/hard?

A

each carbon atom is bonded to 4 others with strong covalent bonds

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20
Q

Why does diamond not conduct electricity?

A

no delocalised electrons

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21
Q

What are graphite’s properties?

A
  • high melting and boiling points
  • soft and slippery
  • conducts electricity
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22
Q

Why does graphite have high melting and boiling points?

A

strong covalent bonds require lots of energy to overcome

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23
Q

What makes graphite soft and slippery?

A

layers can slide over each other as they are held together by weak intermolecular forces

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24
Q

Why does graphite conduct electricity?

A

delocalised electrons are free to move and can carry a charge through the structure

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25
Q

What is metallic bonding?

A

bonding between metal atoms

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26
Q

What is a the structure of a metal?

A
  • +ve metal ions
  • sea of delocalised electrons
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27
Q

What type of bonding occurs in metals?

A

metallic bonding

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28
Q

What are the properties of metals?

A
  • high melting and boiling points
  • conduct electricity
  • malleable
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29
Q

Why do metals have high melting and boiling points?

A
  • strong metallic bonds
  • strong electrostatic forces of attraction between +ve metal ions and delocalised electrons
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30
Q

Why do metals conduct electricity?

A

delocalised electrons are free to move and can carry a charge through the structure

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31
Q

Why are metals malleable?

A

layers can slide over each other

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32
Q

What is electronegativity?

A

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

33
Q

What are the factors affecting electronegativity?

A
  • nuclear charge
  • atomic radius
  • shielding
34
Q

Describe the trend in electronegativity down a group

A

decreases

35
Q

Explain the trend in electronegativity down a group

A

electronegativity decreases as:
- nuclear charge increases
- shielding increases
- atomic radius increases

36
Q

Describe the trend in electronegativity across a period

A

increases

37
Q

Explain the trend in electronegativity across a period

A

electronegativity increases as:
- nuclear charge increases
- shielding remains constant
- atomic radius decreases

38
Q

What is the most electronegative element?

A

fluorine

39
Q

What is the name of the numerical scale of electronegativities?

A

Pauling’s scale

40
Q

How can you determine the type of bonding in a molecule from the electronegativity of the elements?

A
  • if both atoms have a similar electronegativity, they both attract electrons with the same strength therefore the bond is covalent
  • if there is a large difference in electronegativities then the bond is ionic
41
Q

What type of bond is present when the difference in electronegativities of the atoms is less than 0.5?

A

covalent bond

42
Q

What type of bond is present when the difference in electronegativities of the atoms is between 0.5 and 1.7?

A

polar covalent bond

43
Q

What type of bond is present when the difference in electronegativities of the atoms is greater than 1.7?

A

ionic bond

44
Q

What does the shape of a molecule depend on?

A

electron pairs around the central atom (bonding and lone pairs)

45
Q

Why do the electron pairs around the central atom affect the shape of the molecule

A

electrons are all -vely charged so they repel (lone pair charge clouds repel more than bonding pair charge clouds)

46
Q

Order these from smallest to biggest:
- bonding pair - bonding pair angles
- lone pair - lone pair angles
- lone pair - bonding pair angles

A
  • bonding pair - bonding pair angles
  • lone pair - bonding pair angles
  • lone pair - lone pair angles
47
Q

How can the no. of electron pairs in a molecule be used to determine the shape of the molecule?

A
  • work out what the central atom is
  • work out no. of electrons in outer shell of central atom
  • +1 for every atom that the central atom is bonded to (if its an ion after this step +1 for each -ve charge/-1 for each +ve charge)
  • ÷ by 2 to find no. of electron pairs around the central atom
  • compare no. of electron pairs to the no. of bonds to find no. of lone pairs and no. of bonding pairs
  • deduce shape
48
Q

What do wedges represent?

A

bonds going out of the page

49
Q

What do broken lines represent?

A

bonds going into the page

50
Q

What is the shape and bond angle of a molecule with no lone pairs and 2 bonding pairs?

A
  • linear
  • 180°
51
Q

What is the shape and bond angle of a molecule with no lone pairs and 3 bonding pairs?

A
  • trigonal planar
  • 120°
52
Q

What is the shape and bond angle of a molecule with 1 lone pair and 2 bonding pairs?

A
  • bent/non-linear
  • 117.5°
53
Q

What is the shape and bond angle of a molecule with no lone pairs and 4 bonding pairs?

A
  • tetrahedral
  • 109.5°
54
Q

What is the shape and bond angle of a molecule with 1 lone pair and 3 bonding pairs?

A
  • trigonal pyramidal
  • 107°
55
Q

What is the shape and bond angle of a molecule with 2 lone pairs and 2 bonding pairs?

A
  • bent/non-linear
  • 104.5°
56
Q

What is the shape and bond angle of a molecule with no lone pairs and 5 bonding pairs?

A
  • trigonal bipyramidal
  • 90° and 120°
57
Q

What is the shape and bond angle of a molecule with 1 lone pair and 4 bonding pairs?

A
  • seesaw
  • 87° and 102°
58
Q

What is the shape and bond angle of a molecule with 2 lone pairs and 3 bonding pairs?

A
  • T-shaped
  • 88°
59
Q

What is the shape and bond angle of a molecule with no lone pairs and 6 bonding pairs?

A
  • octahedral
  • 90° and 180°
60
Q

What is the shape and bond angle of a molecule with 2 lone pairs and 4 bonding pairs?

A
  • square planar
  • 90°
61
Q

Why are some covalent bonds polar?

A

difference in electronegativities so bonding electrons more strongly attracted to more electronegative atom

62
Q

Why are covalent bonds between atoms of the same element always non-polar?

A

no difference in electronegativity so electrons are equally attracted to both atoms

63
Q

What are the 3 types of intermolecular force?

A
  • permanent dipole - dipole forces
  • van der waals forces
  • hydrogen bonding
64
Q

Order the 3 types of intermolecular force from strongest to weakest

A
  • H bonds
  • permanent dipole - dipole forces
  • van der waals forces
65
Q

What is a dipole?

A

difference in charge between 2 atoms

66
Q

What does δ+ mean?

A

slightly +ve charge

67
Q

What does δ- mean?

A

slightly -ve charge

68
Q

What causes molecules to be polar?

A

if a molecule has polar bonds it may result in an uneven distribution of charge throughout the molecule causing it to be polar

69
Q

Why do the charges cancel out sometimes in molecules with polar bonds?

A

if the bonds are arranged symmetrically then the charges cancel out

70
Q

What occurs between molecules with permanent dipoles?

A

weak electrostatic forces of attraction between δ+ and δ- charges on neighbouring molecules

71
Q

How do temporary dipoles occur?

A
  • electrons are constantly moving
  • uneven distribution of electrons causes δ+ and δ- charges in the molecule causing a temporary dipole
72
Q

How do van der waals forces occur between molecules?

A
  • temporary dipole in 1 molecule can induce another temporary dipole in the opposite direction on a neighbouring atom
  • the 2 dipoles are then attracted to each other
73
Q

Why are temporary dipoles constantly being created and destroyed?

A

because electrons are constantly moving

74
Q

How does the size of a molecule affect the strength of van der waals forces?

A

the larger the molecule the stronger the van der waals forces because larger molecules have larger electron clouds

75
Q

How does the strength of van der waals forces affect melting and boiling points?

A

the stronger the van der waals forces, the higher the melting and boiling points as more energy is required to overcome the forces

76
Q

What elements does hydrogen have to be covalently bonded to in order to be able to form a H bond and why?

A
  • fluorine
  • oxygen
  • nitrogen
  • F, O and N are all very electronegative so they draw bonding electrons further away from H atom causing the H atom to be δ+
  • H atoms form weak bonds with lone pairs on the F/O/N atoms of other molecules
77
Q

Why do substances with H bonds have higher melting and boiling points than other molecular substances?

A

H bonds are the strongest type of IMF

78
Q

What are the 2 anomalous properties of ice?

A
  • relatively high meting and boiling points due to H bonding
  • less dense than water as H2O molecules are further apart in the lattice than in liquid water

A-LEVEL CHEM (6 decks)

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