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Chemistry ATAR 11 > Intermolecular Forces > Flashcards

Intermolecular Forces Flashcards

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1
Q

What does the VSEPR Theory stand for?

A

valance shell electron pair repulsion theory

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2
Q

What is the VSEPR Theory?

A
  • molecular shape results from repulsion between groups of electrons, both bonding and non-bonding, in the valence shell of the central atom
  • allows valence electron groups to have greatest possible angle of separation
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3
Q

1 or 2 groups of electrons

A

linear

180 degrees

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4
Q

3 groups of electrons

A

triangular planar

120 degrees

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5
Q

4 groups of electrons

A

tetrahedral

109.5 degrees

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6
Q

4 groups of electrons, 1 lone pair

A

pyramidal

107.5 degrees

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7
Q

4 groups of electrons, 2 lone pairs

A

bent/V shape

104.5 degrees

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8
Q

Electronegativity

A

the ability of an atom to attract electrons to itself and is measured on a scale of 0 to 4
higher electronegativity = greater tendency to attract electrons

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9
Q

Electronegativity in covalent bonds

A
  • different electronegativity = uneven sharing

- shared electrons will spend more time near the more highly electronegative element

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10
Q

More electronegative element

A

delta minus

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11
Q

Less electronegative element

A

delta plus

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12
Q

A bond with charged ends

A

Bond dipole

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13
Q

Polar molecules

A

molecules with slight positivity and slight negative charged ends
said to have net dipole
all molecules with a single bond dipole

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14
Q

If a molecule has several bond dipoles they may….

A

reinforce one another or cancel each other’s effect (depends on strength and direction of individual bond dipoles)

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15
Q

Non-polar

A

If bond dipoles are equal of size and act in symmetrically opposing directions (cancel out each other’s effects)
has zero net dipole

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16
Q

Polar

A

non-symmetrically arranged
have net dipole
pull in a particular direction

17
Q

dipole-dipole forces

A

attraction occurs between oppositely charged ends of a polar molecule
electrons are pulled towards the more electronegative molecule

18
Q

Effects/Properties of dipole-dipole

A

increase melting/boiling points
solubility
ability to dissolve ionic solutes

19
Q

Increasing melting/boiling points (DIPOLE-DIPOLE)

A

the higher the polarity the higher the melting/boiling points (than other substances of similar molecular size)

20
Q

Solubility (DIPOLE-DIPOLE)

A 
polar substances (dipole-dipole) will dissolve in one another but not in non-polar substances (ones that can't interact by dipole-dipole forces)
LIKE DISSOLVES LIKE
21
Q

Ability to dissolve ionic solutes

A

due to attraction between the dipole of a polar molecule and an ions charge
ion-dipole forces (NOT type of intermolecular force)

22
Q

Dispersion forces

A

occurs in ALL molecular materials
only intermolecular force present in NON-POLAR substances eg. hydrocarbons, N2, O2, CO2
typically weak for molecules with few electrons
show increasing strength for molecules with greater number of electrons (seen in NON-POLAR)
Stronger in molecules who’s shape allows max surface contact between molecules (e.g. linear vs branched or spherical - hight melt/boil points)
dispersion forces increases with molar mass/molecular size

23
Q

Temporary dipoles

A

random motion of electrons within a molecule produce short lived dipoles
can make non-polar molecules temporarily polar
cause nearby molecules to form similar temporary dipoles (INDUCED dipoles)

24
Q

Hydrogen bonding

A

strong as 12% of the carbon to carbon covalent bond
only occur in H-F, H-O, H-N
due to the electrostatic attraction between a lone pair of electrons of F,O,N and H atom already covalently bonded to another F,O,N
Melt/boil points are much higher
extremely soluble in other substances with can also hydrogen bond

25
Q

Intermolecular forces and physical properties

A

melting/boiling points
solubility
equilibrium vapour pressure/vapour pressure

26
Q

melt/boil points (PHYSICAL PROPERTIES)

A

as intermolecular forces present in a substance increase in strength so does its melting/boiling points
substances that interact by dispersion forces as molecular mass increases so does melting/boiling points
substance that interact by dipole-dipole forces will have slightly higher melting/boiling points
hydrogen bonds = even higher melting/boiling points

27
Q

Solubility (PHYSICAL PROPERTIES)

A

Like dissolves like

28
Q

Equilibrium vapour pressure/vapour pressure (PHYSICAL PROPERTIES)

A

a measure of the tendency of a substance to evaporate and is measured in kPa
weak intermolecular forces correspond to liquids that easily evaporate and have a high vapour pressure
increases with temp
weakest intermolecular forces has the highest vapour pressure

Chemistry ATAR 11 (7 decks)

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