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A Level Chemistry > Chapter 6 - Shapes of molecules and intermolecular forces > Flashcards

Chapter 6 - Shapes of molecules and intermolecular forces Flashcards

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1
Q

What are permanent dipole-dipole interactions?

A

The δ positive and δ charges on polar molecules cause weak electrostatic forces of attraction between molecules

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2
Q

What is the strongest intermolecular force?

A

Hydrogen bonding

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3
Q

When will hydrogen bonding occur?

A

When hydrogen is bonded to something very electronegative, e.g. fluorine, nitrogen or oxygen
or when a lone pair of electrons are attracted to the hydrogen

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4
Q

How to show a hydrogen bond?

A

A dashed line

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5
Q

Two molecules with hydrogen bonding

A

Ammonia and water

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6
Q

Why do water, ammonia and hydrogen fluoride have such high m and b points?

A

A lot of energy is needed to overcome the hydrogen bonds

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7
Q

What happens to covalent bonds during melting and boiling?

A

They don’t break - only the weak intermolecular forces do

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8
Q

Why is ice less dense than water?

A

The hydrogen bonds hold the atoms in the lattice far apart from each other. When ice melts, the lattice collapses and the atoms move closer together; water is more dense than ice

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9
Q

Why do boiling points increase as you go down group 7?

A

The number of electrons in the element increases, so the strength of the induced dipole-dipole interaction increases

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10
Q

Why do simple covalent compounds have such low m and b points?

A

Little energy is needed to overcome the intermolecular forces

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11
Q

Why are polar molecules soluble in water?

A

Water is a polar molecule. Compounds with hydrogen bonds form hydrogen bonds with water molecules so will be soluble

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12
Q

Why don’t simple covalent compounds conduct electricity?

A

Covalent molecules are uncharged

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13
Q

What are the three types of intermolecular forces?

A

Induced dipole-dipole interactions
Permanent dipole-dipole interactions
Hydrogen bonding

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14
Q

Which is the strongest intermolecular bond?

A

Hydrogen bonding

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15
Q

What will induced dipole-dipole forces do?

A

Cause all atoms to be attracted to eachother

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16
Q

How do London forces work?

A

Electrons in charge clouds are moving rapidly. At any one moment, there will be more electrons on one side than the other. This causes a temporary dipole. This induces a temporary dipole on a neighbouring atom, in the opposite direction. They are then attracted to each other

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17
Q

What will happen to the London forces if there are more electrons?

A

The stronger the instantaneous dipole will be. This makes the atoms more attracted to eachother

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18
Q

Why do stronger induced dipole-dipole forces cause higher boiling points?

A

In bigger atoms with more electrons, the dipole-dipole forces are stronger and so take more energy to overcome

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19
Q

What is responsible for holding molecules in a lattice?

A

Induced dipole-dipole forces - atoms are held together by covalent forces but the molecules are held together by induced dipole-dipole interactions

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20
Q

Why is the boiling point of hydrogen chloride higher than for just fluorine?

A

Fluorine molecules are non-polar and so only have London forces between
HCl molecules are polar so have London forces AND permanent dipole-dipole interactions between molecules, which requires more energy to overcome

21
Q

What is a simple molecular substance?

A

Made up of simple molecules, forming a simple molecular lattice

22
Q

Bonding in a simple molecular lattice

A

Atoms within each molecule are held together by strong covalent forces but the molecules themselves are held together only by weak intermolecular forces

23
Q

Why do simple molecules have such low melting points?

A

The intermolecular forces are weak

24
Q

When will non-polar simple molecular structures be soluble and why?

A

In non-polar solvents - intermolecular forces form between the molecules and the solvent
These weaken the lattice so it dissolves

25
Q

When will polar molecules be soluble and why?

A

In polar solvents - the two attract each other

26
Q

What is electronegativity?

A

An atom’s ability to attract an electron pair

27
Q

Strongly electronegative elements

A

Oxygen, nitrogen, chlorine and fluorine

28
Q

What will happen in a covalent molecule which is polar?

A

The electrons will move to the more electronegative element

29
Q

What happens when a polar bond is created?

A

A permanent dipole is created

30
Q

Why is the bond in Cl2 non-polar?

A

The two atoms have the same electronegativity

31
Q

When will a bond be non-polar?

A

When the bonded atoms are the same or the electronegativity of the two atoms is similar

32
Q

Why is hydrogen chloride a polar bond?

A

The chlorine is more electronegative, so the electrons move in that direction, creating a permanent dipole

33
Q

Why is water polar?

A

The two O-H bonds have a permanent dipole, which act in different directions. The oxygen molecule has the delta negative charge

34
Q

Bonding in ammonia

A

One lone pair, all bond angles 107

35
Q

Bonding in water

A

Two lone pairs, all bond angles 104.5

36
Q

Bonding in methane

A

No lone pairs, all bond angles are 109.5

37
Q

What is the name of the shape with two bonded and two lone pairs?

A

Non-linear, 104.5 degrees

38
Q

What does a solid line represent?

A

A bond in the plane of the page

39
Q

What does a solid wedge represent?

A

Comes out of the paper

40
Q

What does a dotted line represent?

A

Goes into the plane of the paper

41
Q

What happens with each lone pair?

A

The bond angle decreases by 2.5 degrees

42
Q

What is a lone pair of electrons?

A

One which isn’t shared

43
Q

Why will electrons repel each other?

A

They are both negatively charged

44
Q

What is the name of the shape with four bonded pairs?

A

Tetrahedral, 109.5 degrees

45
Q

What is the name of the shape with three bonded pairs and one lone pair?

A

Pyramidal, 107 degrees

46
Q

Why is carbon dioxide non-polar?

A

The polar bond are arranged symmetrically so cancel each other out

47
Q

Why will NaCl be soluble in water?

A

The Na+ is attracted to the O2-

The Cl- is attracted to the H+, so the structure dissolves

48
Q

What is the order of repulsion?

A

Lone pair/lone pair angles are biggest
Lone pair/bonding pair are second biggest
Bonding pair/bonding pair are smallest

49
Q

What is a hydrogen bond?

A

The attraction between the lone pair of electrons on one electronegative atom in one molecule and a hydrogen atom in another molecule attached to an electronegative atom

A Level Chemistry (29 decks)

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