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.

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.
- the elements contained are always found in the same proportions

Question 2

what is a molecule?

Answer 2

a group of two or more atoms, held together by chemical bonds
- can contain multiple different elements (e.g. water, carbon dioxide), or be two or more of the same element (e.g. oxygen)
- water and carbon dioxide are also compounds

Question 3

what does the size of an atom depend on?

Answer 3

the element it forms

Question 4

what is a mixture?

Answer 4

consists of two or more elements or compounds combined together. the chemical properties of each substance in the mixture are unchanged, as they haven’t reacted with each other
- 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 5

describe the history of the atom:

Answer 5

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, discrete particles. experiments showed that atoms simply couldn’t be solid spheres
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.

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

Question 6

how did ernest rutherford develop his nuclear model?

Answer 6

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 7

what was the flaw with rutherford’s nuclear model?

Answer 7

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 8

describe the method of filtration:

Answer 8

• separates insoluble solids and liquids.

1. place filter paper over a filter funnel, place in beaker to catch the liquid
2. pour solution into funnel, the liquid drips through the filter paper (has lots of tiny holes that water can drip through but not solids), the solids stay in the funnel.

Question 9

describe the method of evaporation:

Answer 9

• separates soluble (dissolved) solids and liquids

1. a solution is placed in an evaporation dish 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 as the solute becomes more concentrated
3. this forms dry crystals of the solid in the basin, with all the solvent having disappeared

Question 10

what are the positives and negatives of evaporation?

Answer 10

good: quick and easy method
bad: some solids decompose when heated (thermal decomposition), so we’d isolate it but break it down into something else. we can counter this by crystallising the solution instead, which is a slightly slower process

Question 11

describe the method for crystallisation:

Answer 11

• to separate soluble solids (subject to thermal decomposition) from a solvent

1. place the solution in an evaporating dish and heat it, but more gently (e.g. use a water bath)
2. once some of the solvent has evaporated and crystals begin to form, stop heating the solution and leave it to cool
3. as the solution cools, more crystals will start to form, as solids are less soluble in colder temperatures
4. filter out these crystals from the remaining solution, using a filter paper and funnel
5. dry out the collected crystals, by leaving them somewhere warm or warming them in the oven

Question 12

what’s the difference between a solution and a mixture?

Answer 12

• putting an insoluble substance in a liquid forms a mixture
• putting a soluble substance in a liquid forms a solution, where the soluble substance is the solute and the liquid is the solvent

Question 13

describe the method of chromatography:

Answer 13

• 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 14

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

Answer 14

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

Question 15

describe the method of simple distillation:

Answer 15

• separates out a liquid from a solution (e.g. to separate pure water from sea water)

1. heat the solution, until one of the liquids begin to evaporate.
2. the vapour from the solution rises and the pressure forces it down a condenser, causing it to cool and condense back into liquid form, which will run down the condenser and collect in the beaker

Question 16

describe the setup for simple distillation:

Answer 16

• flask containing solution/liquid mixture
• beneath the flask is some sort of heating device, e.g. bunsen burner
• the flask is sealed at the top with a bung, so no gas can escape
• put a thermometer through the bung to measure the temperature inside the flask
• a condenser is attached to the neck of the flask, which consists of the main pipe, surrounded by a water jacket, which contains a stream of continually flowing cold water
• at the end of the condenser is a beaker to catch the pure liquid

Question 17

describe the method of fractional distillation:

Answer 17

• separates multiple liquids with different boiling points (a mixture)

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 18

what is the point of the glass rods in the fractionating column?

Answer 18

some of the other liquids will try and evaporate when it’s not their time to leave, and so when they come into contact with the glass rods, which are cooler than their boiling point, they’ll condense back into liquid form and fall back into the flask

Question 19

what are the key features of a fractionating column?

Answer 19

• full of little glass rods, providing a large surface area
• the column, due to its height, is cooler at the top than at the bottom

Question 20

why is fractional distillation used for alcohol?

Answer 20

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

Question 21

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

Answer 21

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 22

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

Answer 22

electron: almost 0
proton: 1
neutron: 1

Question 23

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

Answer 23

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 24

what is the size of an atom?

Answer 24

has a radius of about 1 x 10^-10 metres

Question 25

what is the size of the nucleus of an atom compared to the entire atom?

Answer 25

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 26

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

Answer 26

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 27

what are isotopes?

Answer 27

atoms of the same element can have different numbers of neutrons, these atoms are called isotopes of that element. - the other definition is atoms that have the same atomic numbers but different mass numbers

Question 28

do all isotopes still react in the same way?

Answer 28

yes, as even though the neutron numbers vary, they don't affect how the atom reacts

Question 29

describe the three isotopes of hydrogen:

Answer 29

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 30

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

Answer 30

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 31

what is meant by a stable/unstable atom?

Answer 31

stable: full outer shell (2/8) unstable: incomplete outer shell, so wants to react with other atoms to form molecules/compounds to gain a full outer shell

Question 32

describe dobereiner's triads:

Answer 32

- 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 33

how did dmitri mendeleev organise the periodic table?

Answer 33

- 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 34

describe the periodic table:

Answer 34

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 35

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

Answer 35

- 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 36

what do the atoms in each period have in common?

Answer 36

all have the same number of shells

Question 37

describe the noble gases:

Answer 37

- group 0/8. - they're very unreactive (they're stable, with a full outer shell). exist as single atoms, due to their unreactivity - not flammable - they have very low boiling points (makes sense, they're gases). - the boiling points increase as you go down the group. - colourless gases

Question 38

what colours are the halogens?

Answer 38

- halide salts (e.g. KCl, Kbr, Ki) are colourless - bromine water is orange - chlorine water is colourless - iodine water is brown

Question 39

describe group 1 metals:

Answer 39

- alkali metals. - group 1 metals are soft - all group 1 metals react rapidly with oxygen, chlorine and water, and the reactions become more extreme as you go down the group. - relatively low melting and boiling points, which decrease as you go down the group - low density (li, k, na are less dense than water)

Question 40

how do group 1 metals react with water?

Answer 40

creates a metal hydroxide and a gas - as you go down the group, they become more reactive, and so produce more energy. from potassium downwards, it produces so much energy that it reacts with the hydrogen gas, forming flames

Question 41

how do group 1 metals react with oxygen?

Answer 41

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 42

what can lithium react with oxygen to form?

Answer 42

lithium oxide (Li2O)

Question 43

what can sodium react with oxygen to form?

Answer 43

- sodium oxide (Na2O) - sodium peroxide (Na2O2)

Question 44

what can potassium react with oxygen to form?

Answer 44

- potassium peroxide (K2O2) - potassium superoxide (KO2)

Question 45

how do group one metals react with chlorine?

Answer 45

produces metal chlorides. - often form ionic compounds with non-metals as they lose an electron so easily that non-metals can pick up - they're then attracted together due to their opposite charges, forming an ionic compound - these ionic compounds tend to be white solids (salts) and dissolve in water to form colourless solutions

Question 46

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

Answer 46

- radius of the atoms increases - greater distance between nucleus and electron, meaning the negative electron is less attracted to the positive 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 47

compare metals and non-metals:

Answer 47

metals: - metallic bonding: very strong, responsible for metals' physical properties - malleable - good conductors of heat and electricity - nearly all have high boiling and melting points - shiny - sonorous (create ringing sound when hit) non-metals: - dull in colour - brittle - low melting and boiling points (many are gaseous at room temperature) - poor conductors of electricity - less dense than metals

Question 48

describe group 7 elements (the halogens):

Answer 48

- every group 7 element forms a molecule consisting of two atoms joined by a covalent bond. DIATOMIC MOLECULES - can also form covalent bonds with other non-metals (simple molecular structures) - 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

Question 49

why does reactivity decrease as you go down the halogen group?

Answer 49

the outermost shell gets further and further away from the nucleus, so the attractive force needed to pull in another electron gets weaker. if the halogen can't attract an electron to complete its outer shell, it can't react

Question 50

how do the halogens change their names when they form ions?

Answer 50

become halides

Question 51

what compounds do halogens typically form?

Answer 51

ionic compounds with group 1 metals

Question 52

describe each of the halogens:

Answer 52

- fluorine: poisonous yellow gas, very reactive - chlorine: poisonous green gas, less reactive - bromine: reddy-brown volatile liquid, poisonous - iodine: dark grey solid that can form poisonous purple vapours. also forms an antiseptic, which has saved millions of lives

Question 53

does an atom's mass change on the moon?

Answer 53

no, the mass stays constant across all environments

Question 54

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

Answer 54

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 55

what is the relative atomic mass of an element?

Answer 55

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

Question 56

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

Answer 56

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 57

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

Answer 57

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 58

what are the transition metals?

Answer 58

metals with similar properties which are different from those of the elements in group 1. found in the centre of the periodic table 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 can form multiple different ions with different charges, form coloured compounds, and are useful as catalysts.

Question 59

name some examples of transition metals as catalysts:

Answer 59

- iron is used as a catalyst in the Haber process - nickel is used as a catalyst in the hydrogenation of alkenes