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C2 Flashcards

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1
Q

How did Dmitri Mendeleev organise the elements in his periodic table?

A

In order of atomic mass.

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2
Q

What did Mendeleev have to do in order to keep elements with similar properties in the same groups?

A

He had to swap some elements around and leave gaps.

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3
Q

Why did Mendeleev leave gaps in his periodic table?

A

He predicted the properties of so far undiscovered elements. When they were found and fit the pattern, it helped to confirm Mendeleev’s ideas.

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4
Q

How are elements displayed in the modern periodic table?

A

It shows the elements in order of ascending atomic number.

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5
Q

What are groups in the periodic table?

A

The table is laid out so elements with similar chemical properties form columns known as groups.

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6
Q

What does the group of an element correspond to?

A

The number of electrons it has in its outer shell. For example, Group 1 elements have 1 outer shell electron.

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7
Q

What are periods in the periodic table?

A

Rows of the table.

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8
Q

What does the period of an element correspond to?

A

The number of shells of electrons that it has.

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9
Q

What are ions?

A

Charged particles - when atoms lose or gain electrons to form ions, they are attempting to get a stable electronic structure.

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10
Q

What type of ions do metals and non-metals form?

A

Non-metal - negative

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11
Q

Which groups of atoms most readily form ions?

A

Group 6 and 7 - non-metals, which gain electrons to form negative ions (anions)

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12
Q

Why do Group 1 and 2 get more reactive as you go down the groups?

A

The electron shells are further away from the nucleus as you move down the groups, and it is therefore easier for them to lose electrons

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13
Q

Why do Group 6 and 7 get less reactive as you go down the groups?

A

The electron shells are further away from the nucleus as you move down the groups, and it is therefore more difficult to attract additional electrons.

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14
Q

What is an ionic bond?

A

When a metal and a non-metal react together, the metal can lose electrons to form a cation and the non-metal can gain electrons to form an anion. These oppositely charged ions are attracted by electrostatic forces and form an ionic bond.

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15
Q

What do dot and cross diagrams show?

A

They show the arrangement of electrons in an atom or ion. They can also show what happens to the electrons when atoms react with each other.

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16
Q

What don’t dot and cross diagrams show?

A

The structure of a compound

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17
Q

What are the properties of an ionic compound?

A

They always have a giant ionic lattice structure - the ions form a closely packed regular lattice. There are very strong electrostatic forces of attraction between oppositely charged ions. They have high melting/boiling points and don’t conduct electricity unless molten.

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18
Q

What does a ball and stick model show?

A

It shows the arrangement of ions.

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19
Q

What doesn’t a ball and stick model show?

A

The scale is wrong - there aren’t large gaps inbetween the ions, and the ions aren’t all the same size.

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20
Q

Why do ionic compounds have high melting and boiling points?

A

It is due to the strong attraction between their ions. It takes a huge amount of energy to overcome this attraction.

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21
Q

Why don’t solid ionic compounds conduct electricity?

A

The ions are fixed in place and can’t move.

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22
Q

What is a covalent bond?

A

It is when non-metal atoms combine together and share electrons, in order to gain a full outer shell.

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23
Q

Why are covalent bonds strong?

A

There is a strong electrostatic attraction between the positive nuclei of the atoms and the negative electrons in each shared pair.

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24
Q

What structure do substances formed with covalent bonds usually have?

A

Simple molecular structures

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25
Q

What are the properties of a simple molecular structure?

A

The atoms within the molecules are held together by very strong covalent bonds. However, the intermolecular forces are extremely weak and they therefore have low melting/boiling points. They don’t conduct electricity, as they have no free electrons.

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26
Q

What are the properties of a giant covalent structure?

A

The atoms are bonded to together with extremely strong covalent bonds, and they therefore have high melting/boiling points.

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27
Q

Why is carbon so important?

A

Carbon can form lots of different types of molecule, because carbon atoms can form up to four covalent bonds, and bond easily to other carbon atoms to make chains and rings.

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28
Q

What are the important forms of carbon?

A

Diamond, Graphite, Graphene and Fullerenes

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29
Q

What are the physical properties of diamond?

A

They are lustrous (sparkly) and colourless. Ideal for jewellery.

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30
Q

How many bonds does each carbon form in diamond?

A

Four covalent bonds, in a very rigid giant covalent structure, which makes diamond really hard.

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31
Q

Why does diamond have a very high melting point, and why doesn’t it conduct electricity?

A

It has a very high melting point as it has incredibly strong covalent bonds.
It doesn’t conduct electricity as it has no free electrons.

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32
Q

What are the physical properties of graphite?

A

It is black and opaque, but still somewhat shiny.

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33
Q

How many bonds does each carbon form in graphite?

A

Three covalent bonds, creating sheets of carbon atoms which are free to slide over each other.

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34
Q

Why is graphite ideal for pencils and as a lubricating material?

A

They sheets of carbon atoms are held together weakly and so they are slippery. Therefore, they can be rubbed onto paper to leave a black mark.

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35
Q

Why does graphite have a high melting point?

A

The covalent bonds need lots of energy to break.

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36
Q

Why is graphite able to conduct electricity?

A

Only three of each carbon’s four electrons are used in bonding, and so there are lots of delocalised electrons that can move and conduct.

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37
Q

What is graphene?

A

A single sheet of graphite. Its covalent bonds make it strong and its so thine that it’s transparent and very light. Its delocalised electrons are completely free to move about and so it is an even better conductor than graphite.

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38
Q

What is a fullerene?

A

A form of carbon. They aren’t giant covalent structures, they’re large molecules shaped like hollow balls or tubes.

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39
Q

How are carbon atoms arranged in fullerenes?

A

In rings, similar to those in graphite.

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40
Q

Why are fullerenes able to conduct electricity?

A

They have delocalised electrons and so they conduct.

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41
Q

How is something defined as a nanoparticle?

A

Its a tiny particle which can be between 1 and 100 nanometres.

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42
Q

What is an example of a nanoparticle?

A

Fullerenes, which contain nanotubes.

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43
Q

What is a nanotube and why are they very strong?

A

They are tiny hollow carbon tubes and are strong because of all the covalent bonds.

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44
Q

How do you calculate surface area to volume ratio?

A

Surface area ÷ volume

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45
Q

What is the surface area to volume ratio like in a nanoparticle?

A

Extremely high

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46
Q

What does the surface area to volume ratio mean for a nanoparticle?

A

It gives them different properties from larger particles, because a much larger proportion of their atoms are able to interact with substances that they interact with.

47
Q

What is the use of nanoparticles known as?

A

Nanoscience

48
Q

Why can nanoparticles be good catalysts?

A

They have a high surface area to volume ratio

49
Q

Why do nanoparticles make good suncreams and deodrants?

A

The small particles achieve their job and don’t leave white marks on the s kin.

50
Q

What is the idea of nanomedicine?

A

The idea is that tiny fullerenes could be absorbed more easily by the body than most particles. This means that they could deliver drugs right into cells where they are needed.

51
Q

What can nanotubes be used for?

A

Tiny electric circuits in computer chips

52
Q

What do nanoparticles do to plastic?

A

It makes it much stronger and more durable, whilst adding hardly any mass.

53
Q

How can nanoparticles affect polymer fibres?

A

It can give them antibacterial properties to be used in surgical masks and wound dressings

54
Q

Why is it important that nanoscience products are tested thoroughly?

A

The way that nanoparticles affect the human body is not yet fully understood.

55
Q

What is a polymer?

A

They are formed when lots of small molecules called monomers join together. This is known as polymerisation.

56
Q

What kind of environment is needed for polymerisation?

A

High temperatures and a catalyst

57
Q

What are the atoms in a polymer chain held together by?

A

Strong covalent bonds

58
Q

Why are some polymers/plastics stretchier than others?

A

If it is made up of chains that are held together by weak intermolecular forces, then they will be free to slide over each other. This also means that they have low melting points.

59
Q

Why are some polymers/plastics more rigid than others?

A

Some have stronger bonds between the polymer chains - these might be covalent bonds. These will have higher melting points, are rigid and can’t be stretched.

60
Q

What are cross-links?

A

Strong covalent bonds which are present in rigid plastic

61
Q

Why are metals surrounded by a sea of delocalised electrons?

A

In metals, the outer electrons of each atom can move freely.

62
Q

What is metallic bonding?

A

The electrostatic attraction between the positive metal ions and the sea of delocalised electrons.

63
Q

What are some properties of metals?

A

They are hard, dense and lustrous (shiny)

64
Q

Why are the metallic bonds very strong?

A

There’s an incredibly strong attraction between the delocalised electrons and the closely packed positive ions.

65
Q

What do the strong metallic bonds cause?

A

It causes metals to have high melting and boiling points. You need a lot of energy to break the bonds.

66
Q

Why are metals good conductors of heat and electricity?

A

This is due to the sea of delocalised electrons which move freely through the metal, conducting heat and electricity.

67
Q

What happens when a metal reacts with oxygen?

A

They form a metal oxide. Most metal oxides are solid at room temperature and form basic solutions when you dissolve them in water.

68
Q

What is an alloy?

A

The properties of metals can be changed by mixing them with other elements (either metals or non-metals), which forms an alloy.

69
Q

What are some common properties of non-metals?

A

They usually have low melting and boiling points and, when solid, they tend to be weak and brittle. They usually have lower densities and don’t conduct electricity.

70
Q

Recap the melting/boiling points of different structures

A

Giant covalent - high

71
Q

What does the term “pure” mean?

A

A pure substance in chemistry is a substance made up of a single element or compound

72
Q

What is a mixture?

A

If there is more than one compound present, or different elements that aren’t part of the same compound, you have a mixture.

73
Q

How can you can test the purity of a substance?

A

You can test the purity of a sample by comparing the actual melting or boiling point of the sample to the expected value.

74
Q

How is the melting point different if a substance is impure?

A

The melting point will be too low - eg. if ice melts at -2, it’s probably got an impurity

75
Q

How is the boiling point different if a substance is impure?

A

The boiling point will be too low - eg. the boiling point of sea water is 100.6 rather than 100

76
Q

What is another way of testing if a solid/liquid is pure or not?

A

You can heat it - in a mixture, different components will melt or boil at different temperatures and so different parts of the mixture will melt/boil first. This means that mixtures melt over a range of temperatures.

77
Q

Why is simple distillation used?

A

Separating out a liquid from a solution.

78
Q

Where is the sample to be distilled poured in simple distillation?

A

Into the distillation flask

79
Q

What do you connect the bottom end of the condenser to in simple distillation?

A

A cold tap using rubber tubing - you have to run cold water through the condenser to keep it cool

80
Q

What happens when you heat the distillation flask in simple distillation?

A

The part of the solution that has the lowest boiling point evaporates - eg. in seawater, the water

81
Q

What happens after part of the solution evaporates in simple distillation?

A

The water vapour passes into the condenser where it cools and condenses. It then flows into a beaker where it is collected.

82
Q

What remains in the distillation flask?

A

The part of the solution which wasn’t the liquid eg. in seawater, salt

83
Q

What is the problem with simple distillation?

A

It can only be used to separate things with very different boiling points.

84
Q

What is fractional distillation?

A

It is used when there is a mixture of liquids that you want to separate.

85
Q

What happens when you heat the mixture in the flask in fractional distillation?

A

The different liquids/substances will have different boiling points and will therefore evaporate at different temperatures.

86
Q

Which liquid evaporates first in fractional distillation?

A

The liquid with the lowest boiling point.

87
Q

What happens when the the temperature in fractional distillation matches the substance that is evaporating?

A

The substance will rise to the top of the fractionating column and can be collected.

88
Q

What do you do after collecting the first liquid in fractional distillation?

A

You raise the temperature again until it reaches the temperature of the next substance’s boiling point and repeat.

89
Q

When is filtration used?

A

To separate an insoluble solid from a liquid. It can also be used in purification.

90
Q

How does filtration work?

A

You use filter paper in a funnel and pour your mixture into it. The liquid part of the mixture runs through the paper and a solid residue is left behind.

91
Q

When is crystallisation used?

A

To separate a soluble solid from a solution

92
Q

How does crystallisation work?

A

Once some of the solvent evaporates, or crystals start to form, remove the dish from the heat. As it cools, the soluble solid will start to form crystals.

93
Q

What is chromatography?

A

A method used to separate and identify the substances in a mixture

94
Q

What is the mobile phase in chromatography?

A

Where the molecules can move. This is always a liquid or gas.

95
Q

What is the stationary phase in chromatography?

A

Where the molecules can’t move. This can be a solid or a really thick liquid.

96
Q

What happens to the components of a mixture during chromatography?

A

The components in the mixture separate as the mobile phase moves over the stationary phase. This happens because the chemicals in a mixture spend different amounts of time in the mobile phase/stationary phase.

97
Q

What is the stationary phase in thin-layer chromatography?

A

A thin layer of a solid on a glass or plastic plate

98
Q

What is the mobile phase in thin-layer chromatography?

A

A solvent

99
Q

What is the solvent front in thin-layer chromatography?

A

The distance that the solvent moves

100
Q

How does the solubility of molecules in the solvent affect thin-layer chromatography?

A

The more soluble that a molecule is in the solvent, the more time it spends in the mobile phase and so it’s carried further up the plate.

101
Q

How is paper chromatography different to TLC?

A

It’s mostly the same but it’s stationary phase is a sheet of chromatography paper.

102
Q

What is the result of chromatography analysis?

A

A chromatogram

103
Q

What is the Rf value on a chromatogram?

A

The ratio travelled by the dissolved substance (the solute) and the distance travelled by the solvent.

104
Q

How do you calculate the Rf value?

A

Distance travelled by solute ÷ distance travelled by solvent

105
Q

What is the mobile phase in gas chromatography?

A

An unreactive gas such as nitrogen

106
Q

What is the stationary phase in gas chromatography?

A

A viscous liquid, such as oil

107
Q

What is the first step of gas chromatography?

A

The unknown mixture is injected into a long tube coated on the inside with the stationary phase (a viscous liquid)

108
Q

What happens to the unknown mixture in gas chromatography?

A

It moves along the tube with the mobile phase until it comes out at the other end. The substances are distributed between the phases - each spends a different amount of time in the mobile/stationary phase.

109
Q

What is retention time in gas chromatography?

A

The time it takes for a chemical to travel through the tube. It is different for each chemical and can be used to identify it.

110
Q

How can you find the retention time from a gas chromatography chromatogram?

A

The distance along the x-axis is the retention time which can be used to find out what the chemical is

111
Q

What does the area under a peak show in a gas chromatography chromatogram?

A

The relative amounts of each chemical in the sample

112
Q

What does each peak represent in a gas chromatography chromatogram?

A

A different chemical

113
Q

What is the relative atomic mass of an element?

A

The average mass of one atom of the element, compared to one twelfth of the mass of one atom of carbon-12.

114
Q

What is the empirical formula of a compound?

A

The smallest whole number ratio of atoms in the compound

OCR chemistry (6 decks)

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