Chapter 6 - Shapes of molecules and intermolecular forces Flashcards

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
When will polar molecules be soluble and why?
In polar solvents - the two attract each other
26
What is electronegativity?
An atom's ability to attract an electron pair
27
Strongly electronegative elements
Oxygen, nitrogen, chlorine and fluorine
28
What will happen in a covalent molecule which is polar?
The electrons will move to the more electronegative element
29
What happens when a polar bond is created?
A permanent dipole is created
30
Why is the bond in Cl2 non-polar?
The two atoms have the same electronegativity
31
When will a bond be non-polar?
When the bonded atoms are the same or the electronegativity of the two atoms is similar
32
Why is hydrogen chloride a polar bond?
The chlorine is more electronegative, so the electrons move in that direction, creating a permanent dipole
33
Why is water polar?
The two O-H bonds have a permanent dipole, which act in different directions. The oxygen molecule has the delta negative charge
34
Bonding in ammonia
One lone pair, all bond angles 107
35
Bonding in water
Two lone pairs, all bond angles 104.5
36
Bonding in methane
No lone pairs, all bond angles are 109.5
37
What is the name of the shape with two bonded and two lone pairs?
Non-linear, 104.5 degrees
38
What does a solid line represent?
A bond in the plane of the page
39
What does a solid wedge represent?
Comes out of the paper
40
What does a dotted line represent?
Goes into the plane of the paper
41
What happens with each lone pair?
The bond angle decreases by 2.5 degrees
42
What is a lone pair of electrons?
One which isn't shared
43
Why will electrons repel each other?
They are both negatively charged
44
What is the name of the shape with four bonded pairs?
Tetrahedral, 109.5 degrees
45
What is the name of the shape with three bonded pairs and one lone pair?
Pyramidal, 107 degrees
46
Why is carbon dioxide non-polar?
The polar bond are arranged symmetrically so cancel each other out
47
Why will NaCl be soluble in water?
The Na+ is attracted to the O2- | The Cl- is attracted to the H+, so the structure dissolves
48
What is the order of repulsion?
Lone pair/lone pair angles are biggest Lone pair/bonding pair are second biggest Bonding pair/bonding pair are smallest
49
What is a hydrogen bond?
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