C1 (atomic structure and the periodic table)

Question 1

describe the difference between:
- atoms
- elements
- compounds

Answer 1

atoms: all substances are made of atoms. an atom is the smallest part of an element that can exist. atoms of each element are represented by a chemical symbol.

elements: there are about 100 different elements, shown on the periodic table.

compounds: formed from elements by chemical reactions. always involve the formation of one or more new substances, and often involve a detectable energy change.
- contain two or more elements chemically combined. can only be separated back into elements through chemical reactions.

Question 2

what is a mixture?

Answer 2

consists of two or more elements or compounds combined together. the chemical properties of each substance in the mixture are unchanged.
- can be separated by physical processes such as filtration, crystallisation, simple and fractional distillation, and chromatography.
- these processes do not involve chemical reactions and no new substances are made.

Question 3

describe the history of the atom:

Answer 3

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 4

how did ernest rutherford develop his nuclear model?

Answer 4

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, and the rest simply went through.

Question 5

what was the flaw with rutherford’s nuclear model?

Answer 5

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 6

describe the method of filtration:

Answer 6

• 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 7

describe the method of crystallisation:

Answer 7

• separates dissolved solids and liquids

1. a solution is placed 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 8

describe the method of chromatography:

Answer 8

• 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 9

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

Answer 9

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

Question 10

describe the method of simple distillation:

Answer 10

• separates two liquids with different boiling points.

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

Question 11

describe the method of fractional distillation:

Answer 11

• 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 12

why is fractional distillation used for alcohol?

Answer 12

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

Question 13

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

Answer 13

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 14

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

Answer 14

electron: almost 0
proton: 1
neutron: 1

Question 15

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

Answer 15

protons: +1
electrons: -1
neutrons: 0

• the number of electrons is equal to the number of protons. atoms therefore have no overall charge.
• 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.
• the sum of the protons and neutrons in an atom is its mass number.

Question 16

what is the size of an atom?

Answer 16

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

Question 17

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

Answer 17

the radius of a nucleus is less than 1/10,000 the radius of an atom, but almost all of the atom’s mass is concentrated in the nucleus.

Question 18

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

Answer 18

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 19

what are isotopes?

Answer 19

atoms of the same element can have different numbers of neutrons, these atoms are called isotopes of that element.

Question 20

describe the three isotopes of hydrogen:

Answer 20

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 21

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

Answer 21

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 22

describe dobereiner’s triads:

Answer 22

• 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 23

how did dmitri mendeleev organise the periodic table?

Answer 23

• 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 24

describe the periodic table:

Answer 24

elements arranged in order or atomic number and so that elements with similar properties are in columns (groups). called a periodic table because elements with similar properties occur at regular intervals. elements in the same group have the same number of electrons in their outer shells, so they have similar properties.

• elements that react to form positive ions are metals. the majority of elements are metals, found towards the bottom of the periodic table.
• elements that react to from negative ions are non-metals. these are found towards the right and top of the periodic table.

Question 25

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

Answer 25

• 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 26

describe the noble gases:

Answer 26

• group 0/8.
• 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 27

describe group 1 metals:

Answer 27

• alkali metals.
• 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 28

how do group 1 metals react with water?

Answer 28

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

Question 29

how do group 1 metals react with oxygen?

Answer 29

creates a metal oxide.
- at room temp, oxygen reacts with surface of the metal, forming a white oxide which covers the surface. the metal below the surface doesn’t react.

Question 30

how do group one metals react with chlorine?

Answer 30

produces metal chlorides.

Question 31

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

Answer 31

• 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 32

describe group 7 elements (the halogens):

Answer 32

• 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
• reactivity decreases as you go down the group.
• a more reactive halogen can displace a less reactive halogen from an aqueous solution of salt.

Question 33

does an atom’s mass change on the moon?

Answer 33

no, the mass stays constant across all environments

Question 34

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

Answer 34

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

Question 35

what is the relative atomic mass of an element?

Answer 35

average value that measures the abundance of the isotopes of the element.

Question 36

describe the nature of the compounds formed when chlorine, bromine and iodine react with metals.

Answer 36

chlorine:
reacts vigorously with many metals to form ionic compounds, called metal chlorides. these are generally soluble in water, conduct electricity when dissolved or molten (ionic).

bromine:
forms metal bromides. properties similar to metal chlorides.

iodine:
least reactive among the halogens, reacts slowly with metals. forms metal iodides. shares some similarities with metal chlorides and bromides, but is less soluble in water.

Question 37

describe the nature of the compounds formed when chlorine, bromine and iodine react with non-metals.

Answer 37

chlorine:
reacts with non-metals, including other halogens, to form covalent compounds. exist as diatomic molecules.

bromine:
forms covalent compounds.

iodine:
forms covalent compounds.

Question 38

what are the transition metals?

Answer 38

metals with similar properties which are different from those of the elements in group 1.

share some properties with all metals:
- conduct electricity in solid and liquid states.
- shiny when freshly cut.

most transition metals have, compared to other metals:
- higher melting points
- higher densities
- greater strength
- greater hardness

many transition metals have ions with different charges, form coloured compounds, and are useful as catalysts.