C1 - Atomic Structure And The Periodic Table

Question 1

Describe what is meant by an element, compound, mixture and molecule

Answer 1

Element - a group of the exact same atoms.

Compound - 2 or more elements chemically bonded together.

Mixture - 2 or more elements not chemically bonded.

Molecule - any elements chemically combined, even if they are the same.

Question 2

Describe the physical separation techniques:
- Filtration
- Crystallisation

Answer 2

Filtration is used to separate an insoluble solid from a liquid.
- First, you pour the mixture into a flask through filter paper. The liquid passes through the tiny pores in the filter paper, this is called the filtrate.
- Then, the solid is separated from the liquid as it cannot pass through the filter paper.

Crystallisation is used to separate a soluble solid from a liquid.
- If the solution of the solid and liquid is left for a few days, the water in the solution will evaporate leaving behind crystals of the solid. You can speed up this process by gently heating the solution so the water evaporates faster but you have to be careful because certain chemicals breakdown when heated.

Question 3

Describe simple distillation

Answer 3

Distillation is used when you separate an insoluble solid from a liquid and want to keep the liquid.
- First, the liquid is heated and evaporated so it turns into a vapour.
- Then, the vapour is condensed back into a liquid by cooling.

Method:
1) The solution of the liquid and the dissolved solid is poured into a flask. The flask is connected to a continuous glass tube surrounded by a jacket called the condenser. Cold water runs through the condenser keeping the tube cold.
2) Heat the solution using a bunsen burner so the liquid starts to evaporate.
3) The vapour rises up the glass tube, as it passes over the thermometer, the thermometer reading increases.
4) The vapour passes into the condenser to turn back into a liquid and passes out the tube into a beaker.
5) The flask is left with crystals of the solid.

Question 4

Describe how fractional distillation is used to separate a mixture of liquids

Answer 4

For the liquids to be separated, they must have different boiling points. Fractional distillation can work with many different liquids as long as they have different boiling points.

The apparatus is the same as simple distillation except it has a fractionating column attached to the flask and condensing tube.

1) The mixture is gently heated and both liquids will start to evaporate but the one with the lower boiling point will evaporate more easily.
2) Now there is a mixture of 2 different vapours making their way into the fractionating column where the vapours condense and drip back into the flask to be evaporated again.
3) This repeated evaporation and condensation increases the amount of the lower boiling point chemical in the fractionating column.
4) As the warm vapours pass up the column, the temperature on the thermometer begins to rise which means that a mixture of the two different vapours is passing over the thermometer. However, the vapour mixture contains more of the chemical with the lower boiling point.
5) The vapours now pass into the condenser and turn back into a liquid are collected into a beaker. However, it is still a mixture of the two chemicals.
6) There comes a point where the temperature on the thermometer stops rising, this is the chemical with the lower boiling point and passes through the condenser without the other vapour and can be collected in a fresh beaker. This is the first proper fraction.
7) Later on, the temperature on the thermometer begins to rise again which means that the vapour mixture is passing into the condenser again.
8) When the thermometer reaches a constant temperature, the chemical with the higher boiling point is now being collected.

Question 5

Describe how paper chromatography can be used to separate substances in a mixture

Answer 5

Paper chromatography allows us to separate substances based on their different solubilities.

1) A special paper called chromatography paper is used and a pencil line is drawn near the bottom of the paper.
2) Place dots of your colours on the pencil line apart from each other.
3) The bottom of the paper below the line is placed in a solvent (a liquid that will dissolved substances).
4) The solvent makes its way up the paper and dissolves the inks in the colours.
5) Now the ink is carried up the paper dissolved in the solvent.

-The stationary phase is when the solvent isn’t moving up the papers and bringing the dissolved colours with it.
-The mobile phase is when the solvent is moving up the paper bringing the dissolved colours with it.
-If a colour separates into 2 or more separate colours, it tells us that it was a mixture of the colours. However, if the colour stays the same it was a pure colour.

Question 6

Describe the plum pudding model

Answer 6

The plum pudding model is an atom of positive charge with negative electrons embedded in it.

Question 7

Describe the nuclear model of the atomic structure

Answer 7

-In the nuclear model, most of an atom is simply empty space.
-In the centre there is a positive nucleus which contains most of the mass of the atoms.
-Around the edge are negative electrons.

Question 8

Describe how the nuclear model was modified by the discoveries of electron energy levels, the proton and the neutron

Answer 8

Niels Bohr proposed the idea that electrons orbit the nucleus at specific distances rather than just a general area which was accepted as it agreed with other scientists experiments.

Scientists found that the positive charge in the nucleus is due to protons.

James Chadwick discovered that the nucleus also contains neutral particles called neutrons.

Question 9

State what an isotope is

Answer 9

Isotopes are atoms of the same element with different numbers of neutrons.

Question 10

State what an ion is

Answer 10

Ions are atoms which have an overall charge.
This is because they have lost or gained electrons.

Question 11

What is the formula for relative atomic mass

Answer 11

(Mass number of isotope 1 X percent abundance of isotope 1) + (Mass number of isotope 2 X percentage abundance of isotope 2) / 100

Question 12

Explain why group 0 elements are unreactive

Answer 12

Group 0 elements are not reactive because they have a full outer shell of electrons meaning they are stable.

Question 13

Describe how the boiling points of group 0 elements vary down the group

Answer 13

Noble gases have boiling points all below room temperature, which explains why they are gases.
Their boiling points increase as their relative atomic mass increases.

Question 14

Describe how metals react to form positive ions

Answer 14

When metals react, they lose electrons to achieve a full outer shell. This gives them the stable electronic structure of a noble gas. The metals lose electrons so their overall charge becomes positive meaning they are now known as ions.

Question 15

Describe how group 1 metals react with oxygen, chlorine and water

Answer 15

Group 1 is known as the alkali metals and only have 1 electron in their outer shell.

When group 1 metals react with oxygen they transfer their electron from their outer shell to the oxygen atom but the oxygen atom now has 7 electrons so 2 group 1 metal atoms are needed. At the end of the reaction the group 1 metal atoms have a positive overall charge as they lose an electron. The oxygen still has 8 protons but 10 electrons so it becomes an oxide ion with a negative 2 charge.

When group 1 metals react with chlorine atoms from group 7, they give 1 electron to the chlorine atom. This produces a positive charge metal atom and negative charge chlorine atom.

When group 1 metals react with water they produce a gas and alkali solution rapidly. For example, when lithium reacts with water it produces lithium hydroxide which is an alkali and it also produces hydrogen.

Question 16

Describe how the reactivity of group 1 metals changes as we move down the group

Answer 16

There are two reasons that the reactivity of group 1 metals increase as we move down the group.

1) The radius of the atoms increases meaning there is a greater distance between the positive nucleus and the negative outer electron. As this distance increases, the outer electron is less attracted to the positive nucleus.

2) The outer electron is repelled by electrons in the internal energy levels, which is known as shielding. This decreases the attraction between the nucleus and the outer electron. As we move down group 1, the metals have more electrons in the internal energy levels which means shielding increases.

Question 17

Describe how group 7 elements consist of molecules with two atoms

Answer 17

Group 7 elements are known as halogens and are non metals.

When 2 atoms from group 7 react with each other, they overlap their outer energy levels and form a covalent bond as they share a pair of electrons. Every group 7 element forms a molecule consisting of 2 atoms joined by covalent bonds. Covalent bonds are represented in a stick, e.g. Cl - Cl .

Question 18

Describe how group 7 elements form covalent compounds when they react with non-metals

Answer 18

When halogens react with non metals they form covalent bonds and a covalent compound. For example, when chlorine reacts with hydrogen, they share a pair of electrons as they both need 1 more electron to form a full outer energy level. This forms the covalent compound hydrogen chloride.

Question 19

Describe how group 7 elements form ionic compounds when they react with metals

Answer 19

When halogens react with metals, they form ionic compounds. The halogen gains one electron from the metal and the metal loses an electron. This means that the halogen has an overall charge of -1 and the metal has a overall charge of +1. When halogens form ions, the name of the halogen ends with ide, e.g. chlorine becomes chloride.

Question 20

Describe and explain how the reactivity of the halogens changes down group 7

Answer 20

The reactivity of the halogens decrease as you go down the group.

For example, chlorine is less reactive than fluorine. When a halogen atom reacts with a metal, it gains an electron from the metal atom. Chlorine gains an electron less easily than fluorine for two reasons.
- Firstly, there is a greater distance between the nucleus and outer energy levels compared to a fluorine atom meaning that the outer electrons are less attracted to the nucleus in a chlorine atom compared to a fluorine atom.
- Secondly, there is more electrons in the internal energy levels in chlorine atoms compared to fluorine atoms. The internal energy levels repel the outer electrons which is called shielding. This means that shielding increases as you go down the group.

Question 21

Describe how a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt

Answer 21

When a less reactive compound reacts with a more reactive halogen, the more reactive halogen displaces the less reactive halogen. For example when sodium bromide reacts with fluorine, which is more reactive than bromine, the fluorine can displace the bromine to form sodium fluoride and bromine. This is called a displacement reaction.