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EDEXCEL AS Chemistry > bonding and structure > Flashcards

bonding and structure Flashcards

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1
Q

ionic bonding

A

The electrostatic attraction between oppositely charged ions

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2
Q

ionic compound melting points…

A
  • they have HIGH MELTING POINTS as there are many strong electrostatic forces of attraction between oppositely charged ions
  • lots of energy is required to overcome these forces.
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3
Q

ionic compound melting points…

A
  • they have HIGH MELTING POINTS as there are many strong electrostatic forces of attraction between oppositely charged ions
  • lots of energy is required to overcome these forces.
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4
Q

Do ionic compounds conduct electricity?

A

Yes, when they are dissolved in water or molten. this is due to the ions being free to move

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5
Q

most ionic compounds dissolve in what …?

A

water. this is because water molecules are polar, so they can attract negative and positive ions and break up the structure

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6
Q

ionic compounds are brittle because…

A

when struck with a hammer, layers slide.

as a result, positive ions get aligned with other positives and negative ions align with other negatives.

they repel and the structure breaks apart

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7
Q

how does the size of the charge on an ion affect the strength of an ionic bond?

A
  • the bigger the charge on an ion, the stronger the ionic bond

-more energy is then required to overcome these forces and so they have a high melting and boiling point.

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8
Q

how does the size of the ion (atomic radii) affect the bond strength ?

A
  • the smaller the ion, the stronger the electrostatic attraction between ions.
  • smaller ions can pack together more closely and more energy is required to overcome these stronger forces. the mp and bp are higher
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9
Q

evidence for charged particles…

A

ELECTROLYSIS OF COPPER (||) CHROMATE (VI) ON WET FILTER PAPER.

  • CrCuO4 is dropped onto wet filter paper and electricity is passed through it.
  • positive Cu2+ ions move towards the negative cathode
  • negative CrO4- ions move towards the positive anode
  • opposite charges will attract.
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10
Q

evidence for charged particles…

A

ELECTROLYSIS OF COPPER (||) CHROMATE (VI) ON WET FILTER PAPER.

  • CrCuO4 is dropped onto wet filter paper and electricity is passed through it.
  • positive Cu2+ ions move towards the negative cathode
  • negative CrO4- ions move towards the positive anode
  • opposite charges will attract.
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11
Q

what’s covalent bonding?

A

the strong electrostatic attraction between the shared electrons and positive nucleus

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12
Q

how many electron pairs are in
- a single bond ?
- a double bond ?
- a triple bond ?

A
  • 2
  • 4
  • 6
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13
Q

what is a dative bond / coordinate bond?

A

a covalent bond where both electrons come from one atom. Only atoms with lone pairs can do this.
e.g : NH4+

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14
Q

bond enthalpy is linked to…

A

the length of the bond,
the shorter the bond, the higher the bond enthalpy

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15
Q

what 2 forces balancing is as a result called bond length?

A
  • repulsive forces
  • attractive forces
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16
Q

the effect of electron density on bond length…

A

the greater the electron density between the atoms, the stronger the attractive forces.

this means that the atoms are pulled in further towards each other.

  • this leads to a shorter bond and higher bond density.
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17
Q

shortest bond to longest bond…

A

triple # double # single

high electron density shared = shorter bond and higher bond enthalpy

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18
Q

why do molecules have different shapes and angles?

A

to achieve maximum separation whilst achieving the minimum repulsion

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19
Q

lone pair / bonding pair repulsion (greatest to least)

A

lone pair - lone pair
lone pair - bonding pair
bonding pair - bonding pair

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20
Q

linear shape

A

180 degrees
2 bp
0 lp
e.g: BeCl2

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21
Q

trigonal planar

A

120 degrees
3 bp
0 lp
e.g: BF3

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22
Q

tetrahedral

A

109.5 degrees
4 bp
0 lp
e.g: CH4

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23
Q

trigonal bipyramidal

A

120 and 90 degrees
5 bp
0 lp
e.g: PCl5

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24
Q

octahedral

A

90 degrees
6 bp
0 lp
e.g: SF6

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25
Q

trigonal pyramidal

A

107 degrees
3 bp
1 lp
e.g: NH3

26
Q

bent

A

104.5 degrees
2 bp
2 lp
e.g: H2O

27
Q

square planar

A

90 degrees
4 bp
2 lp
e.g: XeF4

28
Q

3 examples of giant covalent structures

A

diamond, graphite, graphene

29
Q

graphite properties

A

+high melting and boiling point
- many strong covalent bonds

+soft and brittle
- the layers can slide as there are no covalent bonds between them

+Conducts
- delocalised electrons can move around and carry charge

+low density
- layers are far apart in comparison to the covalent bond length

30
Q

diamond properties

A

+ good conductor of heat
- tightly packed ibis arrangement

+ very high mp
- many strong covalent bonds. It’s also very hard

+ doesn’t conduct electricity
- it has no delocalised electrons to carry charge

+ insoluble
- the covalent bonds are too strong to break.

31
Q

graphene properties

A

+ excellent conductor of electricity
- it has delocalised electrons which carry charge

+ high strength
- delocalised electrons strengthen the covalent bonds

+ lightweight and transparent
- it’s only on cell thick
USES… AIRCRAFT SHELLS, PHONESCREENS

32
Q

metallic bonding is…

A

the electrostatic attraction between positive metal ions and the negative delocalised electrons

33
Q

structure of metals…

A

giant metallic lattice

34
Q

metals are good thermal conductors as…

A

the delocalised electrons can transfer kinetic energy

35
Q

metals have a high melting and boiling point because…

A

they have very strong electrostatic attractions

36
Q

solid metals are insoluble because…

A

the metallic bond is too strong to break

37
Q

solid metals are insoluble because…

A

the metallic bond is too strong to break

38
Q

metals are malleable and ductile because…

A

the ion layers can slide when struck and still retain an attraction between ions and delocalised electrons

39
Q

why are metals good electrical conductors?

A

the delocalised electrons are mobile and can carry a current

40
Q

the more electrons an atom can donate to the delocalised system…

A

the higher the melting point

41
Q

electronegativity is…

A

the ability for an atom to attract electrons towards itself in a covalent bond

42
Q

the bigger the difference in electronegativity…

A

the more ionic a compound will be.
- a difference of zero is purely covalent

43
Q

covalent bonds can become polar if…

A

the atoms attached to is have a big difference in electronegativity

44
Q

the bigger the difference in electronegativity…

A

the more polar the bond will be

45
Q

atoms with the same or similar electronegativities are…

A

non polar
- the shared pair of electrons sit in the middle.
cl-:-cl
HYDROCARBONS ARE CLASSED AS NON POLAR MOLECULES.

46
Q

uneven distribution of charge leads to…

A

polar molecules

47
Q

the size of the molecule or atom means what for the london forces?

A

the bigger the molecule or atom, the more london forces you have as you have a larger electron cloud

48
Q

strongest to weakest intermolecular forces (there’s 3)

A

1- hydrogen bonding
2- permanent dipole - dipole forces
3- london forces

49
Q

when we boil a liquid, we’re breaking the…

A

weak london forces, not covalent bonds

50
Q

straight chain hydrocarbons vs branched hydrocarbons london forces

A

straight chain= more hydrocarbons = more energy required to overcome these forces = boiling point increases

branched= they cannot pack together closely = this weakens the london forces between the chains = lower boiling point

51
Q

permanent dipole - dipole interactions exist in…

A

molecules with polarity

52
Q

hydrogen bonding is…

A

the strongest intermolecular force and occurs in very electronegative elements

53
Q

hydrogen bonding occurs between…

A

hydrogen on 1 molecule forms a bond with:
- nitrogen
- oxygen
- fluorine

54
Q

molecules that have hydrogen bonding also have…

A
  • london forces
  • permanent dipole - dipole
55
Q

boiling points of hydrogen halides…
(highest to lowest)

A
  • HF
  • HI
  • HBr
  • HCl
56
Q

polar substances can dissolve in…

A

polar solvents

57
Q

most ionic compounds dissolve in…

A
  • polar solvents
    e.g: H2O
    the - O is attracted to + ions and the + H is attracted to the - ions causing the structure to break down
58
Q

water molecules surround the ions in a process called…

A

hydration

59
Q

alcohols dissolve in…

A

polar solvents as they can hydrogen bond with H2O

60
Q

non polar substances dissolve in…

A

non polar solvents

61
Q

alkanes dissolve best in…

A

non polar solvents as they can form london forces between the molecules

EDEXCEL AS Chemistry (13 decks)

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