Chapter 6: Shapes of molecules and intermolecular forces (6.1, 6.2) Flashcards

1
Q

what are the three types of intermolecular forces (weakest to strongest)

A

induced dipole-dipole interactions (London forces)
permanent dipole-dipole interactions
hydrogen bonding

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2
Q

how do induced dipole-dipole interactions (London forces) come about

A
  • movement of electrons means there will be an uneven distribution of electrons
  • this creates an instantaneous dipole
  • induces/causes dipoles in neighbouring molecule
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3
Q

4 bonded pairs, 0 lone pairs

A

tetrahedral

109.5 degree bond angle

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4
Q

3 bonded pairs, 1 lone pair

A

pyramidal

107 degree bond angle

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5
Q

2 bonded pairs, 2 lone pairs

A

non linear

104.5 degree bond angle

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6
Q

2 bonding regions

A

linear

180 degree bond angle

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7
Q

3 bonded pairs, no lone pairs

A

trigonal planar

120 degree bond angle

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8
Q

6 bonded pairs, no lone pairs

A

octahedral

90 degree bond angle

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9
Q

factors that effect electronegativity

A

different nuclear charges (high nuclear charge means high electronegativity)
atoms may be different sizes (low atomic radius means high electronegativity)
one shared pair of electrons may be closer to one nucleus than the other (closer means high electronegativity)

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10
Q

electronegativity trends in the periodic table

A

electronegativity increases up and along (right) the periodic table

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11
Q

polar bonds

A

the bonded electron pair is attracted more to one of the bonded atoms than the other because it is more electronegative

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12
Q

What effects the strength of induced dipole-dipole interactions?

A

More electrons, larger instantaneous and induced dipoles, the greater the induced dipole, dipole interaction and the stronger the attractive forces between molecules.

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13
Q

Why is the boiling point of a polar substance larger than a non polar substance with the same number of electrons.

A

1) Because non-polar molecules only have london forces
2) Polar substances have London forces and permanent dipole-dipole interactions between molecules
3) More energy is needed to break dipole-dipole interactions

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14
Q

What shape is a carbonate ion?

A

Trigonal planar

CO3 -

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15
Q

What shape is a nitrate ion?

A

Trigonal planar

NO3 -

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16
Q

What shape is a sulfate ion?

A

Tetrahedral

SO4 2-

17
Q

What shape is an ammonium ion ?

A

Tetrahedral

NH4 +

18
Q

How are things charged in a polar molecule?

A

The more electronegative atom is negatively charged (d-) and the other atoms are positively charged (d+)

19
Q

How do you know if a molecule with more than two different atoms is polar?

A

It depends on the shape of the molecule, the dipoles may reinforce each other making a larger dipole or they may cancel each other out.

20
Q

Give an example of where two dipoles cancel each other out to make a non polar molecule?

A

Carbon dioxide

1) The two C=O have a permanent dipole
2) The molecule is symmetrical
3) The dipoles cancels out and the overall dipole is 0

21
Q

Explain how water breaks down a sodium chloride lattice (an ionic substance)?

A

1) Water attracts Na+ and Cl- ions
2) Na+ ions attracted towards oxygen of water molecules and Cl- ions are attracted towards the hydrogen in the water molecules
3) The ionic lattice breaks down and dissolves

22
Q

Why is solid Ice less dense than water?

A

Hydrogen bonds hold water molecules apart further apart in Ice than in water and this open lattice makes solid Ice less dense than liquid water and floats

23
Q

Why does water have a relatively high boiling point?

A

1) Water has london forces but also hydrogen bonds
2) A reasonably large amount of energy is needed to break the hydrogen bonds in water
3) This gives water a higher boiling point than what would be expected from just London forces.

24
Q

how permanent are induced dipoles

A

they are temporary, can appear and then disappear in an instant of time

25
Q

How do elements/ions/compounds get their shapes?

A

Shape is determined by electron pair repulsion
The electron pairs repel one another so they are as far apart as possible
Lone pairs of electrons repel more than bonded pairs of electrons

26
Q

What is a hydrogen bond

A

Intermolecular bonding between molecules containing N, O or F and the H atom of –NH, –OH or HF

27
Q

Solubility of non-polar covalent substances in polar solvents

A

1) Little interaction between molecules in lattice and solvent molecules
2) Bonds in lattice too strong to be broken
3) Tend to be insoluble

28
Q

Solubility of non-polar simple molecular substances

A

When added to a non-polar solvent

1) Intermolecular forces form between molecules and solvent
2) Interactions weaken the intermolecular forces in the simple molecular lattice
3) intermolecular forces break and compound dissolves