bonding Flashcards

1
Q

explain the VSEPR theory

A

pairs of outer electrons arrange themselves as far away from each other to minimise repulsion

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2
Q

what is the name given to a molecule with 4 groups of electrons and what will the bond angle be?

eg CH4

A

tetrahedral

109.5

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3
Q

what is the name + bond angle of a molecule with four groups of electrons, one being a lone pair?

eg - NH3

A

trigonal pydramidal

107

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4
Q

water has four groups of electrons, 2 being lone pairs

name of shape and bond angle?

A

v shaped

104.5 because 2 lone pairs means more repulsion

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5
Q

name + bond angle of a molecule with three groups of electrons + no lone pairs?

A

trigonal planar

120

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6
Q

name and bond angle of a molecule where there are three groups of electrons and one lone pair?

A

bent / v-shaped

117.5

NOT THE SAME AS WATER BECAUSE WATER HAS 2 LONE PAIRS

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7
Q

name and bond angle of a molecule with 2 groups of electrons

A

linear

180

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8
Q

name and bond angle of molecule with five groups of electrons

A

trigonal bipyramidal

90 degrees on one side
120 on other

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9
Q

name and bond angle of molecule with 6 groups of electrons?

A

octahedral

90

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10
Q

list three types of IMF in ascending order of strength

A

van der waals
dipole - dipole
hydrogen

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11
Q

where can dipole dipole forces occur?

A

between molecules with permanent dipoles
molecules with polar bonds

the delta + and delta - regions attract each other to form a lattice structure

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12
Q

why does CO2 not have a dipole moment when it has more than one polar bond?

A

linear molecule so dipoles cancel out

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13
Q

why do vdW occur between all molecules?

A

all atoms/molecules positive and negative charges so are NEUTRAL overall

however they produce weak electrostatic attractions

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14
Q

helium has 2 protons and 2 neutrons and is neutral overall,

how can it have a permanent dipole?

A

at any one time, the electrons could be anywhere
the DISTRIBUTION OF CHARGE is changing at EVERY INSTANT
this means the atom has a dipole at THAT MOMENT

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15
Q

how does an induced dipole occur?

A

the temporary dipole in one atom then affects the distribution of electrons in nearby atoms to form an induced dipole

this atom is then attracted to the original atom for THAT INSTANT

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16
Q

what would create a larger instantaneous dipole?

A

more electrons

17
Q

what does the strength of vdW depend on?

A

Mr - more electrons and so more IM forces

SHAPE - straight chain molecules have more vdW as they can pack more closely together than branched molecules

18
Q

what are the conditions required for hydrogen bonding?

A

a very electronegative atom with a lone pair of electrons covalently bonded to a H atom

(OH or NH group)

19
Q

why is hydrogen bonding so strong?

A

Oxygen atoms in water have lone pairs of electrons

Hydrogen atoms are very electron deficient

so…. lone pair of O on one H2O atom is strongly attracted to electron deficient H atom

20
Q

when do H bonds form?

A
  • when H is covalently bonded to electronegative atom (O or N)
  • the H = + charged to form a bond with lone pair from O or N
  • angle between OH/NH and H bond must be 180
21
Q

what is a simple molecular structure?

A

composed of small molecules (covalent bonding between atoms)

forces of attraction between molecules are much weaker (IMF)

22
Q

what is a macromolecular structure?

A

large number of atoms are linked in a regular 3D arrangement by covalent bonds

DIAMOND AND SILICON DIOXIDE

23
Q

what is a giant ionic structure?

A

lattice of positive electrons each surrounded in a regular arrangement by negative ions

24
Q

what is a metallic structure?

A

regular lattice of positively charged metal ions held together by a sea of delocalised electrons

25
Q

how can mpt/bpt tell us about the type of structure?

A

simple molecular compounds = low (all molecular compounds = covalently bonded)

giant structures = high