Topic 1a - Atoms, Elements, Compounds and Mixtures

Question 1

What is an atom?

Answer 1

All substances are made of atoms. An atom is the smallest part of an element that can exist.

Question 2

What are compounds and how are they formed? (5)

Answer 2

• Compounds are formed from elements by chemical reactions.
• Chemical reactions always involve the formation of one or more new substances.
• Chemical reactions that form compounds, often involve a detectable energy change.
• Compounds contain two or more elements chemically combined in fixed proportions.
• Compounds can be represented by formulae using the symbols of the atoms from which they were formed.

Question 3

What is an ion?

Answer 3

Atom(s) that have lost/gained electrons.

Question 4

What is an element?

Answer 4

Only contains one type of atom

Question 5

What is an elements atomic number?

Answer 5

The number of protons in an atom of an element is its atomic number. All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons.

Question 6

What is the mass number and where is it found?

Answer 6

• The proton number + number of neutrons = mass number
• Found on periodic table, top number

Question 7

What are the number of electrons equal to in an atom?

Answer 7

In an atom, the number of electrons is equal to the number of protons in the nucleus.

Question 8

What is the relative charge of a proton?

Answer 8

+1

Question 9

What is the relative charge of a neutron?

Answer 9

0

Question 10

What is the relative charge of an electron?

Answer 10

-1

Question 11

What is the overall electric charge of an atom?

Answer 11

Atoms have no overall electrical charge.

Question 12

What is the radius of an atom?

Answer 12

Atoms are very small, having a radius of about 0.1 nm.

Question 13

What is the radius of a nucleus?

Answer 13

The radius of a nucleus is less than 1/10 000 of that of the atom => about 1 x 10(-14) m.

Question 14

Where does most of an atoms mass come from?

Answer 14

The nucleus.

Question 15

What is the relative mass of a proton?

Answer 15

1

Question 16

What is the relative mass of a neutron?

Answer 16

1

Question 17

What is the relative mass of an electron?

Answer 17

V.V small

Question 18

What is an isotope?

Answer 18

Different forms of the same element, which have the same number of protons but a different number of neutrons. This means they have the same atomic number but a different mass number.

Question 19

What is relative atomic mass?

Answer 19

The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.

Question 20

How do you calculate relative atomic mass with isotopes?

Answer 20

Relative atomic mass = sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes

abundance = percentage
sum = add both abundances together

Question 21

What do electrons in an atom occupy?

Answer 21

The electrons in an atom occupy the lowest available energy levels (innermost available shells).

Question 22

How can you represent the electronic structure of an atom? (2)

Answer 22

• By numbers => 2,8,8 (1st energy level/shell holds two then everything after is 8)
• By diagram => circles with crosses representing electrons, in the middle write the number of protons + neutrons, and after there are 4 electrons in the outer shell they begin to pair up

Question 23

What do word equations show?

Answer 23

Show what happens in a chemical reaction using the full names of a substance.

Question 24

What do symbol equations show?

Answer 24

Show what happens in a chemical reaction using chemical symbols and formulas.

Question 25

What is a mixture?

Answer 25

A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged.

Question 26

How can mixtures be separated?

Answer 26

Mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography. These physical processes do not involve chemical reactions and no new substances are made.

Question 27

What is the method for Filtration? (4 steps)

Answer 27

1. Fold a piece of filter paper into a cone. You can do this by folding the paper in half and then in half again, and then gently separating one leaf of paper from the rest so that you’ve got a cone shape.
2. Place the filter paper point down into a filter funnel thats sitting in the neck of a container such as a conical flask.
3. Pour the mixture containing the insoluble solid into the funnel lined by the filter paper. Make sure that none of the mixture goes over the top or down the side of the filter paper.
4. The liquid will pass through the filter paper but the solid won’t - it will be left behind in the funnel.

Question 28

What is the 4 step method for evaporation?

Answer 28

1. Pour the solution into an evaporating dish.
2. Place the evaporating dish on top of a tripod and gauze, and place a bunsen burner underneath.
3. Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated. Eventually, the solid will start to reform.
4. Keep heating the evaporating dish until all you have left is a dry solid.

Question 29

What is the 5 step method for crystallisation?

Answer 29

1. Place an evaporating dish on top of a tripod with a gauze mat. Place a bunsen burner beneath the tripod.
2. Pour the solution into the evaporating dish and gently heat it. Some of the solvent will evaporate and the solution will get more concentrated.
3. Once some of the solvent has evaporated, or when you see crystals start to form (the point of crystallisation), remove the dish from the heat and leave the solution to cool.
4. The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution,
5. Filter the crystals out of the solution, and leave them in a warm place to dry. You could also use a drying oven or a desiccator.

Question 30

What is the 3 step method for simple distillation?

Answer 30

1. The equipment is set up and the mixture is heated. The component of the mixture that has the lowest boiling point evaporates.
2. As the vapour rises it passes into the condenser, where it is cooled, condenses (turns back into a liquid) and is collected in a container below the condenser.
3. Components of the mixture with higher boiling points are left behind in the flask.

Question 31

Look at simple distillation labelled diagram on phone.

Answer 31

Rate based on confidence with the labels and the diagram as a whole.

Question 32

What is the 5 step method for fractional distillation?

Answer 32

1. You place the mixture in flask, attach a fractionating column on top and heat it.
2. The different liquids will all have different boiling points - so will all evaporate at different temperatures.
3. The liquid with the lowest b.p. evaporated first. When the temperature on the thermometer matches the b.p. of this liquid, its vapour has reached the top of the column and passed into the condenser. It will then cool and condense into a liquid that can be collected from the bottom.
4. Liquids with a higher b.p. may also evaporate, but they only get so far up the column before condensing back down as the top of the column is cooler than the bottom.
5. When the 1st liquid has been collected, you raise the temperature to the next lowest b.p. of the liquids in the mixture and repeat the steps to collect all of the liquids.

Question 33

What can new experimental evidence lead to?

Answer 33

New experimental evidence may lead to a scientific model being changed or replaced.

Question 34

What were atoms thought to be before the discovery of the electron?

Answer 34

Before the discovery of the electron, atoms were thought to be tiny solid spheres that could not be divided.

Question 35

What did the discovery of the electron lead to?

Answer 35

The discovery of the electron led to the plum pudding model of the atom. The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.

Question 36

Who created the plum pudding model and when?

Answer 36

• J.J Thompson
• 1897

Question 37

What was the alpha particle scattering experiment?

Answer 37

Positively charged alpha particles were fired at an extremely thin sheet of gold. Some particles were deflected, so the plum pudding model couldn’t be right.

Question 38

Who carried out the alpha particle scattering experiment and when?

Answer 38

• Ernest Rutherford
• 1909

Question 39

What did the results from the alpha particle scattering experiment lead to a conclusion of?

Answer 39

The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model.

Question 40

How did Niels Bohr adapt the nuclear model?

Answer 40

Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances - contained in shells and shells were fixed => electrons don’t orbit in random places/ between the shells. The theoretical calculations of Bohr agreed with experimental observations.

Question 41

How were Protons established and when?

Answer 41

Later experiments, including Rutherford and others, led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles => with each particle having the same amount of positive charge - the same as a hydrogen nuclei. The name proton was given to these particles by the 1920s, and this is what scientists referred to them as.

Question 42

What happened 20 years after the nucleus had become an accepted scientific idea?

Answer 42

The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.