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IB Chemistry > Structure 2.2.5-10 & 2.4 > Flashcards

Structure 2.2.5-10 & 2.4 Flashcards

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1
Q

What does bond polarity result from?

A

Difference in electronegativities of bonded atoms

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2
Q

What is electronegativity?

A

Measure of the atom’s relative ability to attract a shared pair of electrons towards itself in a covalent bond

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3
Q

When does a polar bond form?

A

Between two different non-metal atoms with different electronegativites

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4
Q

What will the effect of separation of charge be (in polar bonds)?

A

Making the more electronegative atom appear as if it had a negative pole and the less electronegative atom appear as if it had a positive pole

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5
Q

What makes the bond dipole greater?

A

Greater electronegativity difference

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6
Q

In an oxygen-hydrogen bond, what exists around the oxygen molecule?

A

A permanent negative dipole, due to greater electronegativity

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7
Q

In an oxygen-hydrogen bond, what exists around the hydrogen molecule?

A

A permanent positive dipole, due to less electronegativity

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8
Q

What does molecular polarity describe?

A

The distribution of electrons throughout the whole molecule

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9
Q

What does molecular polarity depend on?

A

Polar bonds within the molecule
Molecular geometry

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10
Q

What makes a covalent molecule non-polar?

A

No polar bonds
If polar bonds are arranged symmetrically and cancel each other out

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11
Q

What makes a covalent molecule polar?

A

If polar bonds are arranged asymmetrically, so don’t cancel each other out

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12
Q

What do carbon and silicon form?

A

Covalent network structures

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13
Q

What do covalent network structures comprise of?

A

Atoms held together by covalent bonds in a continuous 3D lattice

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14
Q

What is an allotrope?

A

Different structural forms of the same element in the same physical state

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15
Q

Why do allotropes have different physical and chemical properties?

A

Different bonding and structural patterns

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16
Q

Structure of a diamond

A

Each carbon atoms are covalently bonded to four other carbon atoms in a tetrahedral shape, with each bond being of equal strength, and each atom packed in the most efficient way. Each carbon atom forms only single bonds

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17
Q

How are carbon atoms packed in a diamond?

A

Most efficient way

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18
Q

What are the characteristics of diamond? Why?

A

Very hard, due to strong covalent bonds
High melting point, due to strong covalent bonds
Poor electrical conductor, as no free moving electrons
Very good thermal conductor

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19
Q

Structure of graphite

A

Each carbon atom forms 3 single covalent bonds with other carbon atom, forming covalently bonded layers of atoms.
The fourth electron is delocalised between layers, and can travel across them.
London dispersion forces between layers are weak

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20
Q

Properties of graphite? Why?

A

High melting point, as carbon atoms are covalently bonded.
Can conduct electricity due to free fourth electron
Soft and slippery, as forces between layers are weak

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21
Q

What type of covalent structure is diamond?

A

Covalent network lattice

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22
Q

What type of covalent structure is graphite?

A

Covalent layer lattice

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23
Q

What is the electron domain geometry / molecular shape of carbon atoms in graphite?

A

Trigonal planar

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24
Q

What is the electron domain geometry / molecular shape of carbon atoms in diamond?

A

Tetrahedral

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25
Q

How do London Dispersion Forces form between layers of graphite?

A

As electrons move, instantaneous dipoles form. This induces a dipole in the above layer, creating LDF

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26
Q

How do delocalised electrons move in graphite?

A

Can travel across layers

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27
Q

Example of a fullerene of carbon

A

C60 buckminsterfullerene

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28
Q

Structure of buckministerfullerene

A

60 carbon atoms arranged into a sphere consisting of 6 and 5 membered rings. Due to incomplete bonding in each carbon, the unpaired electron is delocalised

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29
Q

Properties of C60 buckminsterfullerene

A

Low electrical conductivity as delocalised electron cannot flow easily between molecules

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30
Q

What is the structure of graphene?

A

Single layer of graphite.
Can be rolled into a nanotube

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31
Q

Properties of graphene (according to preliminary results)

A

Stronger than steel/diamond
Better electrical conductivity than copper
better thermal conductor than diamond

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32
Q

Structure of silicon

A

(Same as that of diamond)
Each silicon atom is covalently bonded to four other silicon atoms in a tetrahedral arrangement

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33
Q

How can silicon conduct electricity?

A

At high temperatures, some electrons from covalent bonds are freed, leaving behind a positive hole, which another electron can fill. This process results in the carrying of charge

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34
Q

Structure of silicon dioxide

A

Similar structure to diamond and silicon, based on tetrahedral network arrangement. Each silicon atom is bridged to 4 other silicon atoms via an oxygen bridge. All bonds are covalent, with no free electrons

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34
Q

Does silicon dioxide conduct electricity?

A

No, there are no free-moving electrons

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35
Q

What is the other form that silicon dioxide can exist?

A

Fused quartz, which is formed when molten silicon dioxide is rapidly cooled to form a glass (non-crystalline solid)

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36
Q

Appearance of diamond

A

Transparent, lustruous, crystal

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37
Q

Physical and chemical properties of diamond

A

Hardest known natural substance
Brittle
HIgh MP

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38
Q

Uses for diamond

A

Jewelry
Grinding and cutting glass

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39
Q

Appearance of graphite

A

Grey
Crystalline
Solid

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40
Q

Physical and chemical properties of graphite

A

Soft
Slippery
Brittle
Very high melting point

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41
Q

Uses for graphite

A

Dry lubricant
Pencil lead
Electrodes in electrolysis

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42
Q

Appearance of graphene

A

Transparent

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43
Q

Physical and chemical properties of graphene

A

Thinnest
Strongest
Flexible
Very high melting point

44
Q

Uses for graphene

A

Many applications such as nanotechnology

45
Q

Electrical conductivity of C60 fullerene

A

Non-conductor

46
Q

Thermal conductivity of C60 fullerene

A

Poor conductor

47
Q

Appearance of C60 fullerene

A

black powder

48
Q

Appearance of C60 fullerene

A

Light
Strong
Low MP

49
Q

C60 fullerene uses

A

Lubricants
Nanotechnology

50
Q

Electrical conductivity of silicon

A

Semi-conductor

51
Q

Appearance of silicon

A

Lustruous
Crystal

52
Q

PHysical and chemical properties of silicon

A

Strong
Brittle
High melting point

53
Q

Uses for silicon

A

Electronic

54
Q

Silicon dioxide appearance

A

Transparent to opaque
Crystals

55
Q

Physical and chemical properties of silicon dioxide

A

Strong
brittle
high MP

56
Q

Uses for silicon dioxide

A

Quartz
Glass
Sand

57
Q

Relationship between bond enthalpies and atomic radii

A

Lower atomic radii = higher bond enthalpy

58
Q

What is melting point a good reflection of?

A

Strength of the forces that bond molecules together in a solid

59
Q

General rule for higher melting point meaning…

A

Stronger intermolecular forces

60
Q

Four types of intermolecular forces that hold molecules together in the solid/liquid phase

A

London dispersion forces
Dipole-induced dipole
Dipole-dipole
Hydrogen bonding

61
Q

What happens to intermolecular forces and covalent bonds when heat is applied?

A

Intermolecular forces are disrupted, therefore the substance melts/boils

Strong covalent bonds that hold atoms together remain intact

62
Q

What explains why non-polar molecules liquefying if the temperature is low enough?

A

London Disperson Forces, meaning there is some form of attractive force between non-polar molecules

63
Q

What are London Disperson Forces?

A

Short range, intermolecular forces that are thought to be electrostatic in nature.

They are created by the electron cloud having moments of being unevenly distributed; which generates a temporary, instantaneous dipole ; which induces a dipole in the neighbouring molecule. These temporary dipoles can attract each other but (because they are not permanent) the attraction is weak

64
Q

What substances experience London Dispersion Forces?

A

All molecular

65
Q

What forces influence the strength of the London Dispersion Forces?

A

Size of the molecules
Shape of the molecules

66
Q

Why does the size of the molecules impact LDF?

A

The greater molecular size/mass means more electrons, meaning greater instantaneous dipole, meaning stronger LDFs

67
Q

Why does shape of molecule impact LDF?

A

More compact means smaller surface area between molecules, meaning a weaker attraction

68
Q

What is the relationship between molecular size and boiling point?

A

Larger molecular size (mass)
More electrons
Larger instantaneous dipole
Stronger LDFs
More energy required to overcome intermolecular forces
Higher boiling point

69
Q

What are dipole-induced dipole forces?

A

These forces of atraction occur when a mixture contains polar and non-polar substances.
The presence of a permanent dipole in the polar molecule, such as water, induces a temporary dipole in a
neighbouring non-polar molecule, such as oxygen.

70
Q

What are dipole-dipole forces?

A

These forces of attraction occur between polar
molecules such as hydrogen chloride where the negative
pole on one molecule is atracted to the positive pole on
another molecule.

71
Q

What is the relationship between dipole and melting point, in terms of dipole-dipole forces?

A

Greater dipole
Stronger attraction between molecules
Stronger intermolecular force between molecules
Higher melting point

72
Q

What is hydrogen bonding?

A

When nitrogen/oxygen/flourine (highly electronegative atoms) bond with a hydrogen, the largest possible dipole is created.
Each molecule has one pair of lone electrons (of a NOF) which is attracted to the positive dipole on the adjacent molecule

73
Q

Ranking of intermolecular strength of comparable molecular mass

A

LDF < dipole-dipole < hydrogen bonding

74
Q

What properties of water can hydrogen bonding explain?

A

Relatively high melting and boiling points
Expansion on freezing
Good solvent peroperties

75
Q

What do the physical properties of covalent substance depend on?

A

Whether they are covalent lattice or covalent molecular substances

Covalent lattice substances only contain covalent bonds (which require a lot more energy to break) than the relatively weak intermolecular forces between molecules

76
Q

Volatility

A

Measure of how readily a substance vapourises (liquid -> gas)

77
Q

Electrical conductivity

A

Measure of a substance’s ability to conduct electricity

78
Q

Solubility

A

Measure of a solute’s ability to dissolve in a solvent

79
Q

What does vaporising a molecular substance require?

A

The intermolecular forces between molecules to be overcome.

80
Q

What is the volatility of molecular forces?

A

Generally high, as intermolecular forces are relatively weak so not much energy is required

81
Q

What do stronger intermolecular forces mean for volatility?

A

Stronger intermolecular forces
More energy required to overcome bonds
Higher boiling point
Reduced volatility

82
Q

What happens when a substance dissolves (forces of attraction)?

A

Forces of attraction form between the solvent and the solute

83
Q

When is a covalent molecular substance more likely to dissolve?

A

If the intermolecular forces between solvent and solute are stronger than between molecules of the solute

84
Q

What are polar molecular substances more likely to dissolve in?

A

Polar solvents, as like dissolve like.
For example, the polar molecular substance can form hydrogen bonds with water molecules, meaning the intermolecular forces between the solute and the solvent are stronger than those between the molecules of the solute

85
Q

What are non-polar substances likely to dissolve in?

A

Non-polar solvents

86
Q

What happens when ethanol is mixed with water?

A

The polar -OH group on the ethanol molecule can form a hydrogen bond with water; thus, the ethanol dissolve in water, forming an ion-dipole bond

87
Q

What happens when polar molecular substances mix with water (highly polar)?

A

Either form hydrogen bonds OR ionise in the aqeous solution

88
Q

What does the bonding triangle represent?

A

Bonding as a continuum between the three bonding times, with each being present to different degrees

89
Q

What does the x-axis of the bonding triangle represent?

A

Mean electronegativity of bonded elements

90
Q

What does the y-axis of the bonding triangle represent?

A

Electronegativity difference of bonded elements

91
Q

What is not considered in the bonding triangle?

A

Molecular formula or bond order

92
Q

What is chromatography?

A

A technique used to separate the components of a mixture based on their relative attractions involving intermolecular forces to mobile and stationary phases

93
Q

What is the stationary phase?

A

A solid, or a liquid coating a solid, onto which the componets of a sample adsorb

94
Q

What is adsorption?

A

The attraction or sticking of one substance to the surface of another

95
Q

What is the mobile phase?

A

Gas or liquid which carries the components of a mixture along the stationary phase

96
Q

What does the continual process of chromatographic methods rely on?

A

Continual process of adsorption of components onto the stationary phase and then desorption and dissolving back into the mobile phase

97
Q

What are the factors that affect movement along the chromatography?

A

Attraction between component and stationary phase
Solubility of the component in the mobile phase
Mass of the component

98
Q

What does a greater attraction to the stationary phase rely on?

A

Slower movement along chromatography

99
Q

What does a greater solubility in the mobile phase mean?

A

Faster the movement

100
Q

What does a greater mass of the component mean for paper chromatography?

A

Greater mass, slower movement

101
Q

What are the two types of chromatography?

A

Paper chromatography
Thin-Layer Chromatography (TLC)

102
Q

What is the stationary phase of the paper chromatography?

A

Chromatography paper
Polar -OH groups in the cellulose in the paper can for hydrogen bonds with components with the mixture

103
Q

What is the mobile phase of the paper chromatography?

A

(Depends on the mixture being separated)
Polarity is often an important factor

104
Q

What is the stationary phase of Thin Layer Chromatrography?

A

Uniform layer of silica (silicon dioxide) or alumina (aluminium oxide) coated onto glass/plastic/metal
Polar -OH groups on the surface of the silica and alumina can form hydrogen bonds with components in the mixture

105
Q

What is the mobile phase of thin layer chromatography?

A

(Depends on the mixture being separated)
Polarity is often an important factor

106
Q

Technique of paper chromatography

A
  1. Origin line is drawn towards the bottom of the stationary phase (using pencil)
  2. A small and concentrated spot of a sample of mixture (two or more components) is made on the origin line.
  3. Stationary phase is placed in a vessel containing the slovent starting at a depth below the origin line
  4. The solvent sweeps the componets upwards
107
Q

What is the retardation factor / retention factor (Rf)?

A

Distance travelled by solute from the origin
/
Distance travelled by solvent from the original

108
Q

Why are reactions heated to a constant mass?

A

To ensure no oxygen is remaining in the sample that would impact the result of the actual mass of product

IB Chemistry (10 decks)

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