Topic C2- Elements, Compounds and Mixtures

Question 1

Who was Dmitri Mendeleev?
What did he do?
When did he do it?

Answer 1

Dmitri Mendeleev made the first proper periodic table.

In 1869, he took the 50 known elements at the time and arranged them into his Table of Elements- with various gaps.

He put the elements in order of atomic mass. To keep elements with similar properties in the same vertical groups, he had to swap some elements around- this left a few gaps. He was prepared to leave some very BIG gaps in the first two rows before the transition metals come in on the third row.

The gaps helped to predict the properties of so far undiscovered elements. When they were found and fitted the pattern, it helped to confirm Mendeleev’s ideas.

Question 2

What do the groups (columns) in the periodic table present?

Answer 2

The group to which the element belongs corresponds to the number of electrons it has in the outer shell.

The elements with similar properties formed columns called groups (similar chemical properties react in similar ways).

Question 3

What does the periods (rows) in the periodic table present?

Answer 3

Each new period represents another full shell of electrons. The period to which the element belongs corresponds to the number of shells of electrons it has.

Question 4

How many electrons are allowed in the…:

a. 1st shell
b. 2nd shell
c. 3rd shell

Answer 4

a. 2 electrons
b. 8 electrons
c. 8 electrons.

Question 5

How do you work out the electronic structure of an element from its period and group?

Answer 5

• The number of shells that contain electrons is the same as the period of the element.
• The group number tells you how many electrons occupy the outer shell of the element.

Question 6

Sodium is in period 3 and has 3 shells occupied, and is in group 1- what is its electronic structure?

Answer 6

The first two shells must be full- 2.8
It is in group 1 and has 1 electron in its outer shell.
So the electronic structure must be 2.8.1

Question 7

What is an ion?

Answer 7

Ions are charged particles- they can be single atoms or groups of atoms.

Question 8

What happens when a metal forms an ion?

Answer 8

They lose electrons to form positive ions.

Question 9

What happens when a non-metal forms an ion?

Answer 9

They gain electrons to form negative ions.

Question 10

Which groups are most likely to form ions?

Answer 10

Group 1, Group 2, Group 6, and Group 7.

Question 11

What kind of elements are in groups 1 and 2? What happens when they form ions?

Answer 11

Group 1 and 2 are metals- they lose electrons to form positive ions (cations).

*Cation is a positively charged ion that would be attracted to the cathode in electrolysis.

Question 12

For groups 1 and 2, where are the more reactive elements located?

Answer 12

For groups 1 and 2, the more reactive elements are with increasing periods.

Question 13

For groups 6 and 7, where are the more reactive elements located?

Answer 13

For groups 6 and 7, the more reactive elements with decreasing periods.

Question 14

What happens when a metal and non-metal react together?

Answer 14

• The metal loses electrons to form a positively charged ion
• the non-metal can gain electrons to form a negatively charged ion
• The oppositely charged ions are then strongly attracted to one another by electrostatic forces
• and form an ionic bond.

Question 15

Describe, in terms of electron transfer, how potassium (K) and chlorine (Cl) react to form potassium chloride.

Answer 15

• Each potassium atom loses an electron to form a K+ ion
• each chlorine atom gains an electron to form Cl- ion.
• The oppositely charged ions become attracted to each other by electrostatic forces to form an ionic bond.

Question 16

Give one advantage and one limitation of a dot and cross diagram;

Answer 16

Advantage: Dot and cross diagrams are really useful for showing how ionic compounds are formed

Limitation: but they don’t show the structure of the compound.

Question 17

What kind of structure do ionic compounds have?

Answer 17

• The ionic compounds always have giant ionic lattice structures.
• The ions form a closely packed regular lattice.
• There are very strong electrostatic forces of attraction between oppositely charged ions
• and in all directions.

Question 18

Give one advantage and one limitation of a ball-and-stick model:

Answer 18

Advantage: A ball-and-stick model shows how the ions are arranged.
Limitation: but the scale is wrong- in reality, there aren’t any gaps between the ions, and the ions are different sizes.

Question 19

Give three properties of an ionic compound:

Answer 19

1) Ionic compounds have high melting and boiling points due to the strong attraction between the ions. It takes a large amount of energy to overcome this attraction.
2) Solid ionic compounds don’t conduct electricity because the ions are fixed in place and can’t move. But when an ionic compound melts, the ions are free to move and will carry an electric charge.
3) Many also dissolve easily in water. The ions separate and are all free to move in the solution, so they’ll carry an electric charge.

Question 20

What kind of bond do non-metal atoms form to combine together?

Answer 20

They form covalent bonds by sharing pairs of electrons.

Question 21

Are covalent bonds strong? Why?

Answer 21

• Covalent bonds are strong because there’s a strong electrostatic attraction between the positive nuclei of the atoms
• and the negative electrons in each shared pair.

Question 22

What kind of structure do covalent bonds form?

Answer 22

Simple molecular structures, like CO2, or H2O

Question 23

What are the melting and boiling points in simple molecular structures like?

Answer 23

Simple molecular structures have low melting and boiling points.

Question 24

Are the atoms within the molecules (in simple molecular structures) held weakly or strongly?

Answer 24

The atoms within the molecules are held together by very strong covalent bonds.

Question 25

Are the forces between the molecules (in simple covalent compounds) weak or strong? Why?

Answer 25

• By contrast, the forces of attraction between these molecules are very weak.
• You have to overcome weak intermolecular forces to melt or boil a simple covalent compound.

Question 26

Why are the melting and boiling points in simple molecular structures low?

Answer 26

They are very low because the molecules are easily seperated from each other.

Question 27

What state of matter are simple molecular structures at room temperature?

Answer 27

Either gases or liquids.

Question 28

Do simple molecular structures conduct electricity? Why?

Answer 28

They don’t conduct electricity, they don’t have free electrons or ions.

• they don’t have charged particles that can separate,
• so simple molecular substances cannot conduct electricity
• even when liquid or dissolved in water.
• When simple molecular substances melt or boil, their weak intermolecular forces are overcome
• not the strong covalent bonds.

Question 29

What are Giant Covalent Structures? (4 points)

Answer 29

1) They are similar to giant lattices except that there are no charged ions.
2) The atoms are bonded to each other by strong covalent bonds.
3) This means that they have very high melting and boiling points.
4) They don’t conduct electricity- not even when molten (except for graphite, graphene, and fullerenes)

The only examples you need to know are carbon atoms.

Question 30

Why can carbon form many different types of molecules?

Answer 30

Carbon atoms can form up to four covalent bonds, and bond easily to other carbon atoms to make chains and rings.

Question 31

Give 4 properties of diamond:

Answer 31

1) Pure diamonds are lustrous and colorless.
2) Each carbon atom forms four covalent bonds in a very rigid giant covalent structure, which makes diamonds really hard. This makes diamond an ideal cutting tool.
3) All of those covalent bonds take a lot of energy to break and give the diamond a very high melting point, which is another reason why diamond is a good cutting tool.
4) It doesn’t conduct electricity because it has no free electrons or ions.

Question 32

Give properties of graphite:

Answer 32

Graphite is black and opaque, and slightly shiny.

Question 33

How many covalent bonds does each carbon atom in graphite form?

Answer 33

Each carbon atom only forms three covalent bonds, creating sheets of carbon atoms- which are free to slide over each other.

Question 34

How are the layers of graphite held together (in terms of strength)?

Answer 34

The layers are held together weakly

• so they are slippery and can be rubbed off onto paper to leave a black mark- this is how pencils work.
• This also makes graphite ideal as a lubricating material.

Question 35

Does graphite have a high melting point? Why?

Answer 35

Graphite does have a high melting point- the covalent bonds need loads of energy to break.

Question 36

Does graphite conduct electricity? Why?

Answer 36

Since only three out of each carbon’s outer four electrons are used in bonds, there are a lot of delocalized (free) electrons that can move. This means that graphite conducts electricity.

Question 37

What is graphene? Why is it better than graphite at conducting electricity?

Answer 37

A single sheet of graphite is called graphene. It is transparent and very light. It’s delocalized electrons are completely free to move about, which means it is even better at conducting electricity than graphite.

Question 38

What is a fullerene?

Answer 38

A fullerene is another allotrope of carbon.
They aren’t covalent structures- they are large molecules shaped like hollow balls or tubes. Different fullerenes contain different numbers of carbon atoms.

Question 39

What are the arrangements of the carbon atoms in fullerenes.

Answer 39

The carbon atoms in fullerenes are arranged in rings, similar to those in graphite.

Question 40

Do fullerenes conduct electricity?

Answer 40

They have delocalized electrons, like graphite, so they can conduct electricity.

Question 41

What are the melting and boiling points like in fullerenes?

Answer 41

Their melting and boiling points aren’t anything like as high as those of diamond and graphite, but they’re pretty high for molecular substances because they’re big molecules (and bigger molecules have more intermolecular forces).

Question 42

How big are nanoparticles?

Answer 42

Really tiny particles, 1-100 nanometres (nm) across. (1nm = 0.000 000 001m).

Nanoparticles contain roughly a few hundred atoms- so they’re bigger than atoms and simple molecules but smaller than pretty much anything else.

Question 43

Give one example of nanoparticles:

Answer 43

Fullerenes are nanoparticles- they include nanotubes- tiny hollow carbon tubes. All of the covalent bonds make carbon nanotubes very strong.

Question 44

What is the equation for the surface area to volume ratio?

Answer 44

Surface area to volume ratio = surface area ÷ volume

Question 45

Explain why nanoparticles have a high surface area to volume ratio:

Answer 45

As particles decrease in size, the size of their surface area increases in relation to their volume- so their surface area to volume ratio increases. Nanoparticles have a really high surface area to volume ratio.

Question 46

Why does the really high surface area to volume ratio give nanoparticles different properties from larger particles?

Answer 46

They have a much greater proportion of their atoms which are available to interact with substances they come in contact with.

Question 47

Do nanoparticles make good catalysts?

Answer 47

They have a huge surface area to volume ration so yes, they do make good catalysts.

Question 48

Give three examples of uses of nanoparticles:

Answer 48

1) Nanomedicine: tiny fullerenes are absorbed better by the body than most particles. They can deliver drugs into the cells where they’re needed.
2) Lubricant coatings are being developed using fullerenes. These coatings reduce friction a bit like a really tiny ball bearing and can be used to lubricate artificial joints or gears.
3) Nanotubes conduct electricity, so they can be used in tiny electric circuits for computer chips.

Question 49

Why is it important that nanoparticle products are tested thoroughly?

Answer 49

To minimize the risks; the way they affect the body isn’t fully understood.

**Some people are worried that products containing nanoparticles have been made available before any possible harmful effects on human health have been investigated properly. In other words, the side effects and long-term impacts on health is unknown.

Question 50

What are polymers?

Answer 50

• A long chain of repeating monomers
• A monomer is a type of covalent molecule (behaves differently from simple covalent substances because of the long, thin shapes of their molecules).

Question 51

How are polymers formed?

Answer 51

• Assorted combinations of heat, pressure, and catalysis alter the chemical bonds that hold monomers together
• causing them to bond with one another.
• most often, they do so in a linear fashion,
• creating chains of monomers called polymers

Question 52

Give an example of a polymer:

Answer 52

Plastics are polymers. They are usually carbon based and their monomers are alkenes.

Question 53

What holds the bonds between polymer chains?

Answer 53

Strong covalent bonds.

Question 54

What determines the properties of a plastic?

Answer 54

The strength of the forces between the different chains.

Question 55

Describe what a plastic with weak forces is like:

Answer 55

• If plastic is made up of chains that are only held together by weak intermolecular forces, then the chains will be free to slide over each other.
• This means that the plastic can be stretched easily, and will have a low melting point.

Question 56

Describe what a plastic with strong forces is like:

Answer 56

Some plastics have stronger bonds between the polymer chain- these might be covalent bonds (called cross-links).
-These plastics have a higher melting point, and are rigid, and can’t be stretched, as the cross-links hold the chains firmly together.

Question 57

Two polymers, A and B, are both composed entirely of carbon and hydrogen, Polymer A has a high melting point and is very rigid. Polymer B has a low melting point and is fairly flexible. Suggest why these polymers have different properties, despite being composed of the same elements. (3marks)

Answer 57

• Properties of polymers depend on the forces between the chains.
• The properties of polymers A and B suggest that B has weak intermolecular forces between its chains,
• while it is likely that A has stronger links such as covalent bonds or cross-links between the chains.

Question 58

What structure do metals have?

Answer 58

• Metals consist of giant structures of atoms arranged in a regular pattern
• called a metallic lattice

Question 59

Why do all metals have the same fundamental properties?

Answer 59

• Due to the special type of bonding that exists in metals. -In metals, the outer electron(s) of each atom can move freely.
• The atoms become positive ions in a ‘sea’ of delocalised (free) electrons.
• The metallic bonding is what gives rise to the many properties of metals.

Question 60

What is metallic bonding?

Answer 60

• Metallic bonding is the electrostatic attraction between these ions and electrons.
• The ions are surrounded by the electrons, so the attraction acts in all directions.
• The metallic bonding is what gives rise to the many properties of metals.

Question 61

Give 7 properties of metals:

Answer 61

1) Metals are very hard, dense, and reflective when polished (shiny).
2) There is a strong attraction between the delocalised electrons and the closely packed positive ions- causing very strong metallic bonding.
3) Generally have high melting points and boiling points because of these strong metallic bonds. You need to use a lot of energy to break them apart.
4) Metals have a high tensile strength- strong and hard to break.
5) They can be hammered into different shapes- malleable.
6) They are good conductors of electricity- due to the sea of delocalised electrons which move freely through the metal, carrying the electrical charge.
7) They can also carry heat energy through the metal.

Question 62

How can you form a metal oxide?

Answer 62

• Metal oxides are crystalline solids that contain a metal cation and an oxide anion.
• They typically react with water to form bases or with acids to form salts.
• MO + H2O → M(OH)2 (where M = group 2 metal)
• Thus, these compounds are often called basic oxides.

Question 63

How do you make an alloy?

Answer 63

You can change a metallic substance’s properties by making a mixture with other metals or carbon to make alloys.

Question 64

List 4 properties of non-metals:

Answer 64

1) Low melting and boiling points.
2) When solid, they tend to be weak and brittle.
3) Lower densities than metals
4) Don’t conduct electricity.

Question 65

What properties of copper make it suitable for conducting electricity?

Answer 65

• Copper is a good conductor of electricity as it contains delocalised electrons
• which are free to move and carry an electrical charge.

Question 66

The stronger the bonds are that keep the particles together in a solid or liquid…:

Answer 66

The more heat energy you need to put in to overcome those bonds and separate the particles.

Question 67

Why doesn’t it take much energy to overcome the forces in a simple covalent substance?

Answer 67

• Simple covalent substances have strong bonds within each molecule
• but weak intermolecular forces between the molecules. -So they melt and boil at low temperatures.

Question 68

Why do ionic substances have high melting and boiling points?

Answer 68

• The positive and negative ions in ionic lattices are strongly attracted to each other.
• This strong electrostatic attraction means that they have high melting and boiling points.

Question 69

Why do giant covalent lattices have high melting and boiling points?

Answer 69

They are held together by strong covalent bonds- these take a lot of energy to break, so giant covalent structures have high melting and boiling points.

(In fact, some giant covalent substances sublime instead, this means they go straight from solid into a gas.)

Question 70

What makes a substance ‘pure’?

Answer 70

It is only made up of an element or compound.

Question 71

How can you test the purity of a sample?

Answer 71

You can compare the actual melting or boiling points of the sample to the expected value.

Question 72

How can you identify if a sample is impure?

Answer 72

If the substance is impure, the melting point will be too low relative to the pure substance.

The boiling point of an impure substance will be too high relative to the pure substance.

Question 73

What is distillation used for?

Answer 73

Distillation is used to separate mixtures that contain liquids.

Question 74

How can you use simple distillation to get pure water from seawater?

Answer 74

1) Pour sample of seawater into the distillation flask
2) Set up apparatus (pg 27). Connect the bottom end of the condenser to cold tap using rubber tubing. Run cold water through the condenser t keep it cool.
3) Gradually heat the distillation flask. The part of the solution that has the lowest boiling point will evaporate- in this case it is water.
4) The water vapour passes into the condenser where it cools and condenses. It then follows into the beaker where it is collected.
5) Eventually, you will end with just the salt left in the flask.

Question 75

What is one limitation of simple distillation?

Answer 75

The problems with simple distillation is that you can only use it to separate things with very different boiling points.

Question 76

When do you use fractional distillation?

Answer 76

If you have a mixture of liquids, with similar boiling points, you need to used fractional distillation to separate them.

Question 77

How do you use fractional distillation to separate crude oil?

Answer 77

1) Put mixture in a flask. Attach a fractionating column and condenser above the flask.
2) Gradually heat the flask. The different liquids will all have different boiling points- so they will evaporate at different temperatures.
3) The liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column.
4) Liquids with higher boiling points may start to evaporate. The column is cooler towards the top, to hey will only get part of the way up before condensing and running back down towards the flask.
5) When the first liquid has been collected, raise the temperature until the next one reaches the top.

Question 78

Propan-1-ol, methanol and ethanol have boiling points of 97ºC, 65ºC and 78ºC respectively. A student uses fractional distillation to separate a mixture of these compounds. State which liquid will be collected in the second fraction, explain why?

Answer 78

Ethanol will be collected in the second fraction because it has the second-lowest boiling point of the three compounds in the mixture.

Question 79

What is filtration used for?

Answer 79

It is used to separate an insoluble solid from a liquid.

Question 80

What is crystallisation used for?

Answer 80

It is used to separate a soluble solid from a solution.

Question 81

How do you crystalise a product?

Answer 81

1) Pour solution into an evaporating dish, and gently heat solution. Some of the solvent will evaporate and the solution will be more concentrated.
2) Once some of solvent has evaporated, or when crystals start to form (the point of crystallisation) remove the dish from the heat and leave solution to cool. DON’T completely dry product, as it may decompose.
3) Salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution.
4) Filter the crystals out of solution, and leave them in a warm place to dry. (You could also use a drying oven or a desiccator).

Question 82

What is the chromatography method used to do?

Answer 82

It is used to separate and identify the substances in a mixture. Chromatography has two phases: mobile phase and stationary phase.

Question 83

What is the mobile phases?

Answer 83

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

Question 84

What is the stationary phase?

Answer 84

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

Question 85

What is the mobile phases in thin layer chromatography?

Answer 85

A solvent.

Question 86

How do you perform a thin layer chromatography (TLC) experiment?

Answer 86

1) Draw a line near the bottom of the plate (use pencil- pencil marks are insoluble and won’t move with the solvent as ink might). Put a spot of mixture on the line.
2) Place some of the solvent into the beaker. Dip the bottom of the plate (not spot) into the solvent.
3) Put a watch glass over the beaker to stop the solvent from evaporating.
4) The solvent will start to move up the plate. When the chemicals in the mixture dissolve in the solvent, they will move up the plate too.
5) There will be different chemicals in the sample separated out- forming spots at different places on the plate.
6) Remove the plate from the beaker before the solvent reaches the top. Mark the distance the solvent has moved- called the solvent front- in pencil.

Question 87

What affects the amount of time molecules spend in each phase?

Answer 87

How soluble thye are in the solvent.

How attracted they are to the stationary phase.

Question 88

Describe one difference between paper chromatography and TLC?

Answer 88

Paper chromatography used a sheet of chromatography paper (filter paper) as a stationary phase, whereas in TLC the stationary phase is a thin layer of an inert substance (eg silica) supported on a flat, unreactive surface (eg a glass plate).

Question 89

What is the Rf value?

Answer 89

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

Question 90

What is the formula of the Rf value?

Answer 90

Rf = distance travelled by solute ÷ distance travelled by solvent.

Question 91

How do you find the distance travelled by the solute?

Answer 91

Measure from the baseline to the center of the spot.

Question 92

How can you identify if a substance is pure using chromatography?

Answer 92

A pure substance won’t be separated by chromatography- it will always move as a blob/spot. A mixture will produce multiple blobs/spots.

Question 93

In gas chromatography (GC), what is the mobile phase?

Answer 93

It is an unreactive gas, such as nitrogen.

Question 94

In gas chromatography (GC), what is the stationary phase?

Answer 94

It is a viscous liquid, such as oil.

Question 95

What is the process in gas chromatography (GC)?

Answer 95

1) The unknown mixture is injected into a long tube, which is coated on the inside with the stationary phase.
2) The mixture moves along the tube with the mobile phase until it comes out of the other end. The substances are distributed between the phases (each substance spends a different amount of time dissolved in the mobile phase and stuck to the stationary phase)
3) The time it takes the chemical to travel through the tube is called the retention time.
4) The retention time is different for each chemcial- that is what is used to identify it.

Question 96

What is the chromatogram from GC?

Answer 96

A graph! Each peak on the graph represents a different chemical.

The distance along the X-axis is the retention time- which can be used to identify the chemical.

The relative areas under the peaks show you the relative amounts of each chemical in the sample.

There is one peak for each chemical, which means that a pure substance will only produce a single peak.

Question 97

What is the relative atomic mass (Ar)?

Answer 97

The relative atomic mass of an element is the average mass of one atom of the element, compared to 1/12 of the mass of one atom of carbon-12.

Question 98

What is the relative atomic mass of an element with only one isotope?

Answer 98

Its relative atomic mass will be the same as its mass number.

Question 99

What is the relative atomic mass of an element with more than one isotope?

Answer 99

Its relative atomic mass will be the same as its mass numbers of all the different isotopes, taking into account how abundant each isotope is.

Question 100

What is the relative formula mass (Mr)?

Answer 100

The relative formula mass of a compound is all the relative atomic masses in its formula added together.

**For simple covalent compounds, the relative formula mass is usually called the relative molecular mass.

Question 101

What is graphite?

Answer 101

• Graphite is an allotrope of carbon
• it is an electrical conductor
• a semi-metal.
• Graphite is the most stable form of carbon under standard conditions
• Graphite has a giant covalent structure
• each carbon atom is joined to three other carbon atoms by covalent bonds.
• the carbon atoms form layers with a hexagonal arrangement of atoms.

Question 102

What is the formula of relative atomic mass?

Answer 102

(mass of isotope 1 x %abundance of isoptope 1) +
(mass of isotope x % abundance of isotope 2)
—————————————————————————
100

Question 103

What is the Empirical Formula?

Answer 103

The simplest ratio of atoms (smallest integer number ratio of atoms in a compound)

Question 104

How do you work out the Empirical Formula of Ethane (C2H6)

Answer 104

• The numbers in the molecular formula of ethane are 2 and 6
• Simplify ratio by dividing the largest number that goes into 2 and 6 exactly- that is 2.

C: 2 ÷ 2 = 1
H: 12 ÷ 6 = 3

Empirical formula of ethane is CH3