periodicity, group 2 and group 7

Question 1

how are elements ordered in the periodic table

Answer 1

in rows and columns, in order of increasing proton number

Question 2

period definition

Answer 2

a row in the periodic table

Question 3

group definition

Answer 3

a column in the periodic table

Question 4

ionisation energy definition

Answer 4

the amount of energy required to remove 1 mole of electrons from 1 mole of gaseous atoms forming 1 moles of gaseous 1+ ions

Question 5

are ionisation reactions endothermic or exothermic

Answer 5

they are all endothermic as they all require energy
- this also means they have + enthalpy change values

Question 6

what is electron shielding + how does it affect ionisation energy

Answer 6

the amount of electron shells between nucleus and outermost electron

the more electron shells between the positive nucleus and the negative electron being removed, the smaller the effect of nuclear charge on the electron, and so the less energy is needed to remove it

remember electrons which share a p sub-shell will experience repulsive forces from secondary electron, making it easier to remove

Question 7

what is atomic radius + how does it affect ionisation energy

Answer 7

relates to the size of the atom

the bigger the atom, the further away negative outer electrons are from positive nucleus, the smaller the effect of the nuclear charge is on the electron being removed and so less energy is required to remove it

Question 8

what is nuclear charge and how does it affect ionisation energy

Answer 8

the strength of the positive charge in the nucleus, depending on number of protons

the more protons in the nucleus, the greater the nuclear charge and so the greater the attraction between the nucleus and outer electrons, meaning more energy is needed to remove the electron

Question 9

how does IE change down a group

Answer 9

IE tends to decrease
although nuclear charge increases, shielding and atomic radius also decreases so the effect of nuclear charge on outermost electron decreases so less energy needed to overcome

Question 10

how does IE change across a period

Answer 10

IE tends to increase across a period, as although shielding stays the same, nuclear charge increases and atomic radius decreases as a result, outermost electrons are closer to positive nucleus and experience stronger forces of attraction, so more energy is needed to remove the electron

Question 11

why does IE decrease at group 3 when going across a period

Answer 11

evidence for having subshells
this is where electrons are being removed from p-subshell rather than s-subshell, further away from the nucleus as its a higher energy level so less energy needed to over come nuclear attraction

Question 12

why does IE decrease at group 6 when going across a period

Answer 12

evidence for having electron repulsion in an orbital
first atom where the p orbital is filled with 2 electrons, these repel each other making it easier to remove so less energy required

Question 13

successive ionisation definition

Answer 13

the removal of more than 1 electron from the same atom

Question 14

how does reactivity change as you go down group 2

Answer 14

reactivity increases
group 2 react by losing 2 electrons, going down shielding and atomic radius increase so electrons lost more readily

Question 15

how does boiling point change as you go down group 2

Answer 15

boiling point increases
number of electrons and atomic radius increases so more london forces, more energy to overcome

Question 16

for group 2 elements, why is 2nd IE always greater than 1st IE

Answer 16

+1 ion is smaller than the atom due to the nuclear charge drawing outer electrons in closer, as now there is 1 more proton than electron, so more energy is needed to remove 2nd electron

Question 17

how does melting point change as you go across a period

Answer 17

group 1 - forms giant metallic lattices, high melting point
group 2 - forms giant metallic lattices, even higher melting point as double delocalised electrons and stronger ion charges (2+)
group 3 - forms giant metallic lattices, slightly higher melting point
group 4 - forms giant covalent lattices, highest melting point
group 5 - simple molecular structures held together by london forces, low melting point (slightly lower than 1)
group 6 - forms simple molecular structure, larger than 5 so slightly higher melting point
group 7 - forms diatomic molecules held by simple covalent bonds, low melting point
group 8 - exists as individual atoms, only london forces between them so very low melting point

Question 18

what are observable physical properties of group 7 elements from F to I

Answer 18

F = a pale yellow gas
Cl = a pale green gas
Br = brown-orange liquid
I = grey solid

Question 19

how does reactivity change as you go down group 7

Answer 19

reactivity decreases
group 7 react by gaining 1 electron, as you go down electronegativity decreases because atomic radius and shielding increases, so nuclear attraction decreases so don’t gain electrons as readily

Question 20

how does boiling point change as you go down group 7

Answer 20

boiling point increases
number of electrons and atomic radius increases so more london forces, more energy to overcome

Question 21

what is a halogen displacement reaction and why does it occur

Answer 21

a redox reaction between 2 different halogens, where the more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide

this occurs because halogens are oxidising agents, so the more reactive halogen acts as the oxidising agent, itself becoming reduced to gain an electron

Question 22

what would you observe during a halogen displacement reaction

Answer 22

a colour change
the colour of the solution indicated which free halogen is present in the solution (the one that has been displaced)

Question 23

what can you add to more easily observe the colour change that occurs during a halogen displacement reaction

Answer 23

an organic solvent such as hexane
this will form a coloured band above the aqueous solution as the halogen dissolves in it

Question 24

what colours do Cl Br and I appear in aqueous and organic solvents

Answer 24

aqueous
Cl = pale green/colourless
Br = yellow
I = brown precipitate

organic
Cl = colourless
Br = yellow
I = purple

Question 25

disproportionation definition

Answer 25

a reaction in which the same species is oxidised and reduced

Question 26

equation for the disproportionation reaction between Cl and H20

Answer 26

Cl2(g) + H2O(l)&raquo_space; HCl(aq) + HClO(aq)

Question 27

uses of HClO

Answer 27

HClO = chloric (I) acid
- can sterilise water by killing bacteria
- dissociates to form ClO-
- ClO- can also sterilise water
- it can also act as bleach (will turn indicator red then colourless)

Question 28

equation for the disproportionation reaction between Cl and NaOH

Answer 28

Cl2(g) + 2NaOH(aq)&raquo_space; NaCl(aq) + NaClO(aq) + H2O(l)

Question 29

uses of NaCl and NaClO

Answer 29

• this mixture of compounds is used as bleach
• it is also used to disinfect water/kill bacteria

Question 30

advantages and disadvantages of using compounds of Cl to treat water

Answer 30

advantages
- used to kill bacteria which makes it safer to drink and for use in pools

disadvantages
- potential toxic effects of Cl
- risk of the formation of chlorinated hydrocarbons

benefits to treating water with Cl outweigh the potential risks