C1 (atomic structure and the periodic table)

Question 1

describe the history of the atom:

Answer 1

1. atomic theory (democritus). everything is made up of the smallest particles, surrounded by empty space.
2. ‘solid spheres’ (john dalton). different types of spheres make up different elements.
3. plum pudding model (j.j. thompson). ball of positive charge containing negatively charged particles.
4. nuclear model (earnest rutherford). instead of a general field of positive charge, there’s a compact nucleus, that contains the positive charge. it also has to have a cloud of negative charge around it.
5. electrons (niels bohr). electrons orbit the nucleus in shells, which stops the atom from collapsing.

ernest rutherford found the positive charge in the nucleus to be in small particles (protons). james chadwick discovered neutral particles in the nucleus (neutrons).

Question 2

how did ernest rutherford develop his nuclear model?

Answer 2

took positively charged alpha particles, and fired them at a thin sheet of gold. if the positive charge in the gold atoms was generally spread out, as j.j. thomson proposed, then the alpha particles should pass through the sheet, as the weak, spread out positive charge wouldn’t be enough to affect the particles.

• some of the alpha particles were either deflected out to the sides, or deflected back the way they’d come.

Question 3

what was the flaw with rutherford’s nuclear model?

Answer 3

there was nothing stopping the negative charge from rushing in on the positive nucleus. this means that the atom would automatically collapse, which we know it doesn’t.

Question 4

describe the method of filtration:

Answer 4

• separates insoluble solids and liquids.

1. place filter paper over funnel, place in beaker.
2. pour solution into funnel, the liquid drips through the filter paper, the solids stay in the funnel.

Question 5

describe the method of crystallisation:

Answer 5

• separates dissolved solids and liquids

1. a solution is heated in an evaporation basin and heated by a bunsen burner.
2. the volume of the solution decreases because some of the water evaporates. solid particles begin to form in the basin.
3. take the basin off the bunsen burner, and place it in a dry place for a week, for all the water to evaporate, only leaving crystals at the base.

Question 6

describe the method of chromatography:

Answer 6

• separates solutions with many different dissolved solutes (solids) in the liquid.

1. ink or plant dye is dotted along a pencil line at the bottom of a strip of paper.
2. as the paper is lowered into the solvent, some of the dye spreads up the paper.
3. at the end, the paper will have absorbed the solvent, and the dye will have spread even further up the paper.

Question 7

what is the difference between a solute, a solvent and a solution?

Answer 7

solute: dissolved solid
solvent: liquid in which a solid dissolves
solution: liquid containing a dissolved solid

Question 8

describe the method of simple distillation:

Answer 8

• separates two liquids with different boiling points.

1. heat the solution in a round-bottomed glass above a bunsen burner, until the liquid begins to evaporate.
2. the vapour from the solution rises and passes down a condenser, which cools and condenses back into liquid form.

Question 9

describe the method of fractional distillation:

Answer 9

• separates multiple liquids with different boiling points.

1. place solution in a flask, and heat from below with a bunsen burner. place a fractionating column on top of the flask, connected to a condenser.
2. the solution is heated in the flask, and the temperature is controlled carefully using a thermometer. the liquid with the lower boiling point evaporates first, and is condensed and collected.
3. this is continued for any other liquids, until there’s only one liquid left in the original flask.

Question 10

why is fractional distillation used for alcohol?

Answer 10

when separating water and ethanol, it can purify or strengthen alcohol.

Question 11

how can you check that the liquid produced is fully pure?

Answer 11

boil the liquid again, keeping in mind its boiling point. if it boils at a different boiling point than expected, it isn’t fully pure, and still has other liquids inside it.

Question 12

what are the relative masses of electrons, protons, and neutrons?

Answer 12

electron: almost 0
proton: 1
neutron: 1

Question 13

what are the relative charges of protons, electrons and neutrons?

Answer 13

protons: +1
electrons: -1
neutrons: 0

Question 14

what is the size of an atom?

Answer 14

has a radius of about 1 x 10^-10 metres (0.1 nano-metres)

Question 15

what is the size of the nucleus of an atom compared to the entire atom? (if that makes sense)

Answer 15

the radius of a nucleus is less than 1/10,000 the radius of an atom

Question 16

why do the electrons closest to the nucleus have the least energy?

Answer 16

because more protons are present in the nucleus, the force of attraction between the protons and electrons is stronger. this means the electrons closer to the nucleus have less energy.

Question 17

describe the three isotopes of hydrogen:

Answer 17

protium: 1 proton, 0 neutrons. 99.98% of hydrogen isotopes are protium. it’s used in fuel cells and the production of plastics.

deuterium: 1 proton, 1 neutron. 0.02% of hydrogen isotopes are deuterium. it’s used in nuclear fusion.

tritium: 1 proton, 2 neutrons. very rare. used in thermonuclear fusion weapons.

Question 18

why do elements in the same group react in the same way?

Answer 18

because they all have the same number of electrons in their outer shells. e.g. noble gases react in similar ways because they’re all stable (all have 8 electrons in their outer shells).

Question 19

describe dobereiner’s triads:

Answer 19

• discovered that elements with similar chemical properties often occurred in groups of threes (triads).
• e.g. lithium, sodium, potassium (all react rapidly with water).

Question 20

how did dmitri mendeleev organise the periodic table?

Answer 20

• arranged elements in increasing atomic weight
• switched the order of some elements to fit the patterns of other elements in the same group
• realised some elements had not yet been discovered, and left gaps in the table
• predicted the properties of the undiscovered elements. scientists then believed him.

Question 21

what are the differences between mendeleev’s periodic table and the modern day table?

Answer 21

• in the modern periodic table, elements are arranged in order of atomic number (at mendeleev’s time, protons had not yet been discovered. ordering them by atomic weight is inaccurate, due to the presence of isotopes)
• modern periodic table has group 0 (noble gases) - these were not fully discovered at mendeleev’s time.

Question 22

describe the noble gases:

Answer 22

• they’re very unreactive (they’re stable, with a full outer shell).
• they have very low boiling points (makes sense, they’re gases).
• the boiling points increase as you go down the group.

Question 23

describe group 1 metals:

Answer 23

• group 1 metals are soft
• all group 1 metals react rapidly with oxygen and other gases, including chlorine, and also water, and the reactions become more extreme as you go down the group.
• relatively low melting points
• low density (li, k, na are less dense than water)

Question 24

how do group 1 metals react with water?

Answer 24

• creates an alkali and a gas (e.g. lithium + water = lithium hydroxide + hydrogen)

Question 25

why are elements more reactive as they move down the group?

Answer 25

• radius of the atoms increases - greater distance between nucleus and electron, meaning the electron is less attracted to the nucleus, and so can leave more easily.
• outer electron is repelled by other electrons (shielding), decreasing the attraction between the nucleus and the outer electron. as you move down group 1, there are more internal electron shells, meaning shielding increases.

Question 26

describe group 7 elements (the halogens):

Answer 26

• every group 7 element forms a molecule consisting of two atoms joined by a covalent bond. DIATOMIC MOLECULES
• melting and boiling points increase as you move down the group

Question 27

does an atom’s mass change on the moon?

Answer 27

no, the mass stays constant across all environments

Question 28

how does an atom’s electron arrangement change when it absorbs or emits electromagnetic radiation?

Answer 28

absorbs electromagnetic radiation: electrons move to a higher energy level further away from the nucleus

emits electromagnetic radiation: electrons can drop to a lower energy level, closer to the nucleus