1: Atomic Structure and the Periodic Table

Question 1

describe how compounds, how they are formed, and how they are separated.

Answer 1

they’re formed from elements by chemical reactions and contain two or more elements chemically combined in fixed proportions. they can only be separated into elements by chemical reactions.

Question 2

what do chemical reactions involve?

Answer 2

they always involve the formation of one or more

new substances; often involve a detectable energy change

Question 3

what are diatomic molecules and what are the homonuclear ones?

Answer 3

they’re molecules composed of only two atoms, of the same or different chemical elements
iodine, bromine, chlorine, fluorine, oxygen, nitrogen, hydrogen

Question 4

what are mixtures?

Answer 4

consists of two or more elements or compounds not

chemically combined together - chemical properties of each substance in the mixture are unchanged.

Question 5

list the ways mixtures can be separated.

Answer 5

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

Question 6

describe how you would separate a mixture by filtration.

Answer 6

used for separating an insoluble solid from a liquid
put filter paper in a filter funnel above beaker; pour the mixture of insoluble solid and liquid into the filter funnel; liquid particles are small enough to pass through the filter paper as a filtrate; solid particles are too large to pass through the filter paper and stay behind as a residue.

Question 7

describe how you would separate a mixture by crystallisation.

Answer 7

used to separate a soluble solid from a liquid
place the solution in an evaporating basin and heat with a Bunsen burner; volume of the solution will decreased because some of the solvent has evaporated; solid particles will begin to form in the basin; once all the solvent has evaporated, solid crystals will be left behind.

Question 8

describe how you would separate a mixture by simple distillation.

Answer 8

used for separating the solvent from a solution
solution is heated; solvent begins to evaporate and its vapours rise; vapour passes into the condenser, where it cools and condenses; liquid solvent drips into a beaker placed under condenser; once all the solvent has evaporated from the solution, the solute will be left behind.

Question 9

describe how you would separate a mixture by fractional distillation.

Answer 9

used for separating a liquid from a mixture of two or more liquids
instead of having only one condenser, fractional distillation uses a column with several condensers placed at different heights; distillation column is hotter at the bottom and colder at the bottom; substances w higher boiling points will condense at the bottom of the column; substances w lower boiling points will condense at the top of the column

Question 10

describe how you would separate a mixture by chromatography.

Answer 10

used for separating dissolved substances from one another e.g inks, food colourings and plant dyes
draw a pencil line and place spots of ink/plant dye etc. on it; fill a container of solvent, such as water/ethanol; lower the paper into the solvent; solvent travels up through the paper, taking some of the coloured substances with it; as the solvent continues to travel up the paper, the different coloured substances spread apart.

Question 11

what was the earliest model/theory of the atom

Answer 11

they were thought to be indivisible, little spheres (John Dalton, 1803)

Question 12

what is the plum pudding model?

Answer 12

J J Thomson discovered the electron; which led to creation of p. p. model - the atom is a ball of positive charge with negative electrons embedded in it

Question 13

what is the nuclear model / alpha particle model?

Answer 13

1909, Ernest Rutherford fired positively charged alpha particles at thin gold foil; most alpha particles went straight through the foil; a few were scattered in different directions; led to conc. mass of an atom was concentrated at the nucleus; the nucleus was positively charged. nuclear model replaced the plum pudding model

Question 14

how did Niels Bohr adapt the nuclear model?

Answer 14

suggested that electrons orbit the nucleus at specific distances; theoretical calculations of Bohr agreed with experimental observations.

Question 15

how did Bohr’s model become adapted?

Answer 15

later experiments => nucleus contain smaller particles which had the same amount of positive charge - protons

Question 16

how was the neutron discovered?

Answer 16

experimental work of James Chadwick in 1932 showed existence of neutrons within the nucleus, leading to another development of atomic model, which we use now

Question 17

what is the relative mass and relative charge of a proton?

Answer 17

mass = 1; relative charge = +1

Question 18

what is the relative mass and relative charge of a neutron?

Answer 18

mass = 1; relative charge = 0

Question 19

what is the relative mass and relative charge of a electron?

Answer 19

mass = negligible; relative charge = -1

Question 20

why do atoms have no overall charge?

Answer 20

the number of protons = the number of electrons

Question 21

what is an isotope?

Answer 21

atoms that have the same proton number, but different neutron number

Question 22

how do you calculate the Ar (relative atomic mass)?

Answer 22

Ar = total mass of atoms / total number of atoms

Question 23

how are elements arranged in the periodic table?

Answer 23

all elements in a group have the same number of outer electrons - so similar chemical properties; number of shells = period number

Question 24

describe the early attempts to classify elements.

Answer 24

tried to classify the elements by arranging them in order of their atomic weights; early periodic tables were incomplete - many elements unknown - and some elements were placed in inappropriate groups if the strict order of atomic weights was followed

Question 25

describe how Mendeleev managed to help the development of the periodic table.

Answer 25

arranged the elements in order of increasing atomic weights; also took into account the properties of the elements and their compounds - showed elements with similar chem. properties lined up in groups; left gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights (due to different chem. properties)

Question 26

how was Mendeleev’s table proved reliable?

Answer 26

elements with properties predicted by Mendeleev were discovered and filled the gaps; existence of isotopes explained why the order based on atomic weights was not always correct

Question 27

what kind of ions do metal react to form?

Answer 27

positive ions

Question 28

what kind of ions do non-metals react to form?

Answer 28

negative ions

Question 29

describe the properties of group 0 elements.

Answer 29

called the noble gases; unreactive/inert; do not easily form molecules - their atoms have stable arrangements of electrons; have eight electrons in their outer shell, (except for helium, has two); boiling points increase with increasing relative atomic mass (going down the group)

Question 30

why do the boiling points of noble gases increase going down the group?

Answer 30

atoms become larger; intermolecular forces between atoms become stronger; more energy needed to over these forces

Question 31

describe the properties of group 1 elements (alkali metals).

Answer 31

single electron in their outer shell; form positive ions; are soft (they can be cut with a knife); have relatively low melting points; have low densities; reactivity increases going down group

Question 32

what happens when lithium is added to water? (observation)

Answer 32

fizzes steadily; slowly becomes smaller until it disappears; moves slowly across surface of water

Question 33

what happens when sodium is added to water? (observation)

Answer 33

fizzes rapidly; dissolves in water; quickly moves across surface of water

Question 34

what happens when potassium is added to water? (observation)

Answer 34

burns violently with sparks and a lilac flame; quickly dissolves rapidly, often with a small explosion; rapidly moves across surface of water

Question 35

describe alkali metals’ reaction w oxygen.

Answer 35

reacts to form metal oxides; at room temp. oxygen only reacts w surface of metal; burns vigorously when heated and placed in a jar of oxygen; reactions become more vigorous going down group

Question 36

describe alkali metals’ reaction w chlorine.

Answer 36

react vigorously to form chlorides; at room temp. they’re white solids; dissolve in water to form colourless solutions; reactions become more vigorous going down group

Question 37

why does reactivity increase going down group 1?

Answer 37

atoms become larger; outer electron is therefore further away from the nucleus; the force of attraction between the nucleus and the outer electron decreases; electron is lost more easily

Question 38

describe the properties of group 7 elements (halogens).

Answer 38

simple molecules - molecules made of pairs of atoms joined by a single covalent bond; the further down the group an element is the higher its relative molecular mass, melting and boiling point

Question 39

why do the melting and boiling points increase going down group 7?

Answer 39

molecules become larger; intermolecular forces become stronger; more energy is needed to overcome these forces

Question 40

what do halogens react w metals to form?

Answer 40

salts - ionic compound

Question 41

what do halogens react w hydrogen (non-metal) to form?

Answer 41

hydrogen halide-

Question 42

why does reactivity decrease down group 7?

Answer 42

atoms become larger; outer electron is therefore further away from the nucleus; the force of attraction between the nucleus and the outer shell decreases; harder to gain electron; becomes less reactive

Question 43

how do halogens displace other halogens?

Answer 43

more reactive halogen can displace less reactive halogen from solutions of its salts

Question 44

describe the physical properties of all metals. (2)

Answer 44

conduct electricity in the solid and liquid states; shiny when freshly cut

Question 45

what typical physical properties do only transition metals have (group 1 don’t) (4)?

Answer 45

higher melting points; higher densities; greater strength; greater hardness

Question 46

describe the differences in chemical properties between group 1 metals and transition metals (reactions w oxygen, cold water and halogens).

Answer 46

group 1 react quickly w oxygen, most t metal react slowly, or not at all; group 1 react vigorously w cold water, most t metal react slowly, or not at all; iron reacts w water and oxygen to form rust; group 1 react vigorously w halogens

Question 47

describe typical properties of transition metals.

Answer 47

form differently charged ions (e.g. Fe2+, Fe3+) ; form coloured compounds; they are useful as catalysts - they’re unreactive so can be reclaimed/reused, can form ions w different charges