C1: Atomic structure and the periodic table

Question 1

Atoms have a radius of about…

Answer 1

0.1nm (1x10^-10m)

Question 2

A nanometer is one ___th of a metre.

Answer 2

Billonth.

Question 3

What is one nanometer in standard form?

Answer 3

1x10^-9m

Question 4

The nucleus has a radius of ___, which is around 1/___th the radius of an atom.

Answer 4

1x10^-14m, 1/10,000th

Question 5

What decides what type of atom an atom is?

Answer 5

The number of protons in the nucleus.

Question 6

How many different elements are there?

Answer 6

About 100.

Question 7

What are isotopes?

Answer 7

Different forms of an element which have the same number of protons but different numbers of neutrons.

Question 8

What is relative atomic mass and why is it used?

Answer 8

Because many elements can exist as different isotopes, RAM is used as a mass number. It is an average, taking into account the different masses and their abundances.

Question 9

What formula is used to calculate the RAM of an element?

Answer 9

A_r = sum of (isotope abundance x mass number)

————————————————————

sum of abundances of all isotopes

Question 10

What is a compound?

Answer 10

2 or more different elements, present in fixed proportions, chemically bonded together.

Question 11

What are mixtures?

Answer 11

A substance which consists of 2 or more elements and/or compounds, which can be separated out using physical methods. They are not chemically bonded.

Question 12

Chromatography is used to separate different dyes within an ink. Explain how a chromatography experiment is set up.

Answer 12

1. Draw a line near the bottom of a sheet of filter paper in pencil (since it’s insoluble).
2. Add a spot of ink to this line.
3. Place the sheet in a beaker of solvent (e.g. water - depends on what’s being tested), making sure the ink doesn’t touch the solvent.
4. Put a lid on the container to stop the solvent evaporating.

Question 13

Chromatography is used to separate different dyes within an ink. The following method is used to do this:

1. Draw a line near the bottom of a sheet of filter paper in pencil (since it’s insoluble).
2. Add a spot of ink to this line.
3. Place the sheet in a beaker of solvent (e.g. water - depends on what’s being tested), making sure the ink doesn’t touch the solvent.
4. Put a lid on the container to stop the solvent evaporating.

Explain what will happen during this experiment.

Answer 13

1. The mobile phase (solvent) seeps up the paper, carring the ink with it.
2. Each dye within the ink moves up the paper at a different rate; the dyes separate out into spots.
3. If any of the dyes are insoluble, they stay on the stationary phase (pencil line).
4. When the solvent has nearly reached the top, the paper is taken out and allowed to dry; the result is a chromatogram.

Question 14

What are the mobile and stationary phases in chromatography?

Answer 14

Mobile phase = solvent (bc it moves up the paper).

Stationary phase = pencil line (it doesn’t move).

Question 15

How would you separate an insoluble solid from a liquid?

Answer 15

Filtration.

Question 16

How would you separate a soluble salt from a liquid? Give 2 ways.

Answer 16

1. Evaporation: heating the solution, in an evaporating dish, over a bunsen burner. However, this can only be used if the salt doesn’t thermally decompose. If it does:
2. Crystallisation: gently heating the solution until crystals start to form, then leaving it to cool. More crystals will form, which are filtered out of the solution and left in a warm place to dry.

Question 17

How would you separate out rock salt (a mixture of salt and sand)?

Answer 17

1. Grind it to make the salt crystals small (so that they dissolve easily).
2. Put it in water and heat; salt will dissolve but sand won’t.
3. Filter out the sand.
4. Evaporate the water from the salt, so that it forms dry crystals.

Question 18

What is simple distillation used for?

Answer 18

Separating out a liquid from a solution.

Question 19

How does simple distillation separate out a liquid from a solution?

Answer 19

1. Solution is heated.
2. The part of the solution with the lowest boiling point evaporates first.
3. The vapour is cooled in a condenser, then collected in a beaker at the end of the condenser.
4. The rest of the solution remains in the flask.

Question 20

What is the problem with simple distillation?

Answer 20

You can only use it to separate liquids with very different boiling points.

Question 21

What is fractional distillation used for?

Answer 21

Separating out liquids, from a mixture, with close boiling points.

Question 22

This lab demonstration models the separation of crude oil at a refinery. How does the process work?

Answer 22

1. Heat the mixture in the flask
2. The liquid with the lowest boiling point evaporates first.
3. When the thermometer’s temperature reaches the boiling point of this liquid, it reaches the top of the column, condenses, and is collected.
4. Other liquids may start to evaporate, but will condense part of the way up the column (bc it’s cooler towards the top).
5. Once the first liquid’s collected, the temperature is raised until the next one reaches the top of the column. Etc.

Question 23

What was Dalton’s model of the atom?

Answer 23

Atoms were solid, indivisible spheres. Each element was made of a different type of sphere.

Question 24

What was Thomson’s model of the atom?

Answer 24

He discovered electrons which could be removed from atoms, disproving Dalton’s theory of indivisibility.

Thomson suggested atoms were spheres of positive charge, with negative electrons scattered throughout (plum pudding model).

Question 25

What was Rutherford’s model of the atom?

Answer 25

Positively charged nucleus, surrounded by a cloud of negative electrons. This was the first nuclear model of the atom.

Question 26

What discovery did Bohr make? How was he proven right?

Answer 26

Electrons orbit the nucleus in fixed positions, called energy levels.

His theoretical calculations agreed with experimental data.

Question 27

What discovery was made after electron orbits?

Answer 27

Experiments showed that the nucleus’ positive charge was subdivided between a group of particles, called protons.

Question 28

What discovery did Chadwick make? Why did this make sense?

Answer 28

He proved the existence of neutrons in the nucleus. This explained the imbalance between the atomic and mass numbers.

Question 29

Who theorised that atoms were solid, indivisible spheres?

Answer 29

Dalton.

Question 30

Who theorised the plum pudding model?

Answer 30

Thomson.

Question 31

Whose discoveries led to the nuclear model of the atom?

Answer 31

Rutherford.

Question 32

Who calculated that electrons had fixed orbits?

Answer 32

Bohr.

Question 33

Who discovered neutrons?

Answer 33

Chadwick.

Question 34

How was Rutherford’s alpha scattering experiment conducted?

Answer 34

Scientists in Rutherford’s lab fired a beam of alpha particles at a thin sheet of gold foil.

Question 35

In Rutherford’s alpha scattering experiment, what did the scientists expect to happen and why?

Answer 35

From the plum pudding model, they expected particles to pass straight through the gold foil, or only be slightly deflected.

Question 36

What were the results of Rutherford’s alpha scattering experiment? Why wasn’t this as expected?

Answer 36

The majority of the alpha particles went straight through the gold sheet. However, some were deflected more than expected and a few were deflected right back the way they came. The plum pudding model couldn’t explain this.

Question 37

In Rutherford’s alpha scattering experiment, a few alpha particles were deflected back. What did the scientists deduce from this?

Answer 37

They realised that most of the atom’s mass was concentrated in a central nucleus, which must also have a positive charge, since it repelled the positive alpha particles.

Question 38

In Rutherford’s alpha scattering experiment, most of the alpha particles passed straight through. What did the scientists deduce from this?

Answer 38

They realised that most of the atom is just empty space, and that the nucleus is very small relative to this space.

Question 39

What was deduced from the results of Rutherford’s alpha scattering experiment?

Answer 39

1. Because a few alpha particles were deflected back, they realised that most of the atom’s mass was concentrated in a central nucleus, which must also have a positive charge, since it repelled the positive alpha particles.
2. Because most of the alpha particles passed straight through, they realised that most of the atom is just empty space, and that the nucleus is very small relative to this space.

Question 40

How were elements organised in the early periodic table, and what was the problem with this?

Answer 40

1. Elements were organised according to their relative atomic masses.
2. The table wasn’t complete, and some elements were placed in the wrong group because the ordering didn’t take into account their properties.

Question 41

How was Mendeleev’s periodic table different to - and better than - the early versions of the periodic table?

Answer 41

1. He organised elements mainly in order of atomic mass, but also taking into account their properties.
2. The discovery of isotopes showed he was right to do this.
3. He left gaps which predicted the existence of undiscovered elements, allowing him to predict their properties.
4. The discovery of certain elements that fit this pattern confirmed his ideas, for example, he left a gap for an element with similar properties to aluminium. Gallium was discovered, and it showed these properties.

Question 42

How many elements are there?

Answer 42

About 100.

Question 43

How are elements organised in the modern periodic table?

Answer 43

1. Elements are laid out in order of increasing proton number, meaning there are repeating patterns of properties.
2. Metals on left; non-metals top right.
3. Elements with similar properties form columns: groups. Group no. = no. electrons on outer shell.
4. The rows are periods; the period number shows how many electron shells an element has.

Question 44

Give 4 properties of metals.

Answer 44

1. Strong
2. Malleable and ductile
3. Good conductors of heat and electricity
4. High melting and boiling points: almost always solids at room temp. (exception is mercury)

Question 45

Non-metals form a variety of different structures, sohave a wide range of chemical properties. Give 5 typical properties of non-metals.

Answer 45

1. Dull-looking
2. Brittle
3. Lower density than that of metals
4. Bad conductors of electricity
5. Not always solids at room temp. / lower melting points than metals

Question 46

Transition metals are found in the middle of the periodic table. Give 7 properties of transition metals.

Answer 46

1. Good conductors of electricity + heat
2. Strong
3. Dense
4. Shiny
5. Can form more than one ion
6. Colourful
7. Transition metal compounds often make good catalysts

Question 47

What are group 1 elements known as?

Answer 47

The alkali metals.

These are: lithium, sodium, potassium, rubidium, caesium and francium.

Question 48

Give 3 properties of alkali metals.

Answer 48

1. Soft
2. Low density (lithium, sodium + potassium less dense than water)
3. Very reactive (only 1 electron in outer shell; easily lost)
4. Only ever form ionic compounds (1+ ions)

Question 49

What are the trends in properties of alkali metals as you go down the group?

Answer 49

1. Increasing reactivity
2. Decreasing melting + boiling points
3. Increasing relative atomic mass

Question 50

Alkali metals only ever form ionic compounds. What are these compounds usually like?

Answer 50

White solids that dissolve in water to form colourless solutions.

Question 51

Explain why sodium is more reactive than lithium.

Answer 51

1. Sodium is further down group 1 than lithium.
2. Group 1 ions lose one electron to become stable.
3. Sodium’s outer electron is further from the nucleus that lithium’s.
4. So the electrostatic attraction between the electron and nucleus is weaker.
5. So the electron is more easily released.
6. So sodium is more reactive.

Question 52

Compare the reactions of lithium and potassium with water. Describe what would be observed in each reaction and explain the similarities and differences. (6)

Answer 52

A vigorous reaction would be observed with both metals.

The reaction with potassium would be more vigorous as it is more reactive than lithium. This is because the outer electron of potassium is further from its nucleus and therefore more easily lost.

Both metals would float, as they are less dense than water.

Both metals will fizz, producing bubbles of hydrogen gas.

The reaction with potassium would produce more hydrogen bubbles, as potassium is more reactive.

The reaction with potassium would release more energy, to the extent that the potassium and hydrogen could ignite.

Question 53

Compare the properties of transition and alkali metals.

Answer 53

1. Alkali metals are much more reactive.
2. Transition metals are stronger, denser and harder.
3. Alkali metals have much lower boiling points.

Question 54

How do alkali metals react with water?

Answer 54

1. They react vigorously to produce hydrogen gas and metal hydroxides.
2. The violence of reactivity (and energy released from the reaction) increases as you go down the group.

Question 55

How do alkali metals react with chlorine?

Answer 55

1. When heated in chlorine gas, they form white metal chloride salts.
2. The reaction gets more vigorous as you go down the group.

Question 56

How do alkali metals react with oxygen?

Answer 56

They react with oxygen to form metal oxides (which is why they tarnish in the air), different types of oxide forming depending on the metal:

Lithium → lithium oxide.

Sodium → mixture of sodium oxide and sodium peroxide

Potassium → mixture of potassium peroxide and potassium superoxide

Question 57

What are group 7 elements known as?

Answer 57

The halogens.

Question 58

What are the trends in properties of the halogens as you go down the group?

Answer 58

1. Decreasing reactivity
2. Increasing melting + boiling points
3. Increasing relative atomic masses

Question 59

Give 3 properties of the halogens.

Answer 59

1. Form diatomic molecules
2. Bond ionically w/ metals
3. Bond covalently to form simple molecular compounds
4. A more reactive halogen will displace a less reactive one from an aqueous solution of its salt

Question 60

What is the colour and state of fluorine at room temperature? Give 2 of its properties.

Answer 60

Yellow gas.

Very reactive and poisonous.

Question 61

What is the colour and state of chlorine at room temperature? Give 3 of its properties.

Answer 61

Green gas.

Fairly reactive, poisonous, dense.

Question 62

What is the colour and state of bromine at room temperature? Give 3 of its properties.

Answer 62

Red-brown liquid.

Poisonous, dense, volatile.

Question 63

What is the colour and state of iodine at room temperature? What does its gas look like?

Answer 63

Dark grey, crystalline solid.

Purple gas.

Question 64

A chemist places a glass lid over a beaker containing aqueous iodine. She places an ice cube on top of the lid and then gently heats the solution. Predict and explain her observations.

Answer 64

A purple vapour will form over the solution as the iodine evaporates.

Purple/grey crystals will form on the lid as the iodine deposits/crystallises/solidifies.

Question 65

What are the group 0 elements known as?

Answer 65

The noble gases.

Question 66

Give 4 properties of noble gases.

Answer 66

1. Inert
2. Non-flammable (bc of above)
3. Exist as monatomic gases
4. All colourless gases at room temperature

Question 67

Why are the noble gases inert?

Answer 67

They have full outer shells which are energetically stable. They therefore don’t need to react to gain or lose electrons to become stable.

Question 68

What are the trends in properties of the noble gases as you go down the group?

Answer 68

1. Increasing boiling points (greater no. electrons in each element leads to greater intermolecular forces
2. Increasing relative atomic mass