groups 2 and 7

Question 1

trend in ionisation energies in group 2

Answer 1

Ionisation energy decreases down group 2 because the outer electrons are further from the nucleus and shielding increases, which means the attraction between the nucleus and the outer electrons decreases

Question 2

trend in reactivity in group 2

Answer 2

increases down group 2 because the outer electrons are further from the nucleus and shielding increases, which means less energy is required to remove the outer electrons.

Question 3

reactiosn of oxygen and group 2

Answer 3

• all react with oxygen to form metal oxides eg. 2Mg + O2 –> 2MgO
• except barium!! - forms barium perioxide Ba + O2 —> BaO2, due to bariumslow charge density so can’t polarise the oxygen to break it apart

Question 4

reaction with chlorine and group 2

Answer 4

all react to form metal chlorides XCl2

Question 5

reaction with water and group 2

Answer 5

• all react with water to form metal hydroxide and hydrogen X + 2H2O —> X(OH)2 + H2
• except Magnesium which forms magnesium oxide and H2 in reaction with steam, Mg + H2O —> MgO + H2
• Ba doesn’t react with water at all

Question 6

group 2 oxides as bases

Answer 6

• react with acids to form a salt and water
  eg. MgO + HCl —> MgCl2 + H2O
• react with water to form hydroxides
  eg. MgO + H2O —> Mg(OH)2 + H2

Question 7

Group 2 hydroxides as alkalis

Answer 7

• Dissolve in H2O to release OH- ions (Ca(OH)2 sparingly soluble)
  eg. Mg(OH)2 —> Mg2+ + 2OH-
• react with acids to form a salt and water
  eg. Ca(OH)2 + H2SO4 —> CaSO4 + 2 H2O

Question 8

solubility of group 2 hydroxides and sulfates

Answer 8

solubility of hydroxides increases as you go down the group therefoe the highr conc of OH- ions and becomes more alkaline
solubility of sulfates decrease as you go down the group

Question 9

why do melting points and hardness of group 2 metals decrease down the group but the density increases

Answer 9

ionic radius increases but charge stays the same so charge density of ions decreases so attraction to delocalised electrons decreases so weaker bonding
density increases - mass of nucleus increases faster than the ionic/atomic radius

Question 10

how do flame tests work

Answer 10

when metal compound heated electrons in the metal ions absorb heat energy are excited to higher electronic energy levels.
as the electrons return to their normal energy levels (ground state) the energy is emitted as visible light
The colour of light emitted is characteristic of that metal as each metal has energy levels with different energy gaps between them.

Question 11

flame test colour for lithium

Answer 11

crimson

Question 12

flame test colour for sodium

Answer 12

yellow

Question 13

flame test colour for potassium

Answer 13

lilac

Question 14

flame test colour for beryllium

Answer 14

no collur - wavelength emitted not in visible spectrum

Question 15

flame test colour for magnesium

Answer 15

no colour- wavelength emitte not in visible spectrum

Question 16

flame test colour for calcium

Answer 16

brick red

Question 17

flame test colour for strontium

Answer 17

red

Question 18

flame test colour for barium

Answer 18

pale green

Question 19

flame test colour for copper

Answer 19

green

Question 20

how to carry out a flame tests (method)

Answer 20

• dip nichrome wire in concentrate hydrochloric acid (chlorides evaporate more easily and so colour flames more strongly than less volatile compounds, concentrated hydrochloric acid converts involatile compounds such as carbonates to chlorides)
• dip the nichrome wire in crystals of metal to be tested
• place the nichrome wire in a blue flame from the bunsen burner and note down the colours for each crystal

Question 21

what is thermal decomposition

Answer 21

the breakdown of a compound into two or more different substances using heat

Question 22

trend in themral stability down group 2

Answer 22

more thermally stable ie require more energy to decompose

Question 23

thermal decomposition and group 1 carbonates

Answer 23

all thermally stable at bunsen burner temperatures except for lithium

Question 24

thermal decomposition equation for group 2 carbonates and lithium carbonate

Answer 24

Li2CO3 —> Li2O + CO2
CaCO3 —> CaO + CO2

Question 25

thermal decomposition and group 2 carbonates

Answer 25

lithium and all of group 2 decompose to give the metla oxide and CO2

Question 26

how does thermal decomposition work in group 2 elements

Answer 26

if metla ion has high enough charge density then elctron cloud become distorted ie polarised c-o bond is weakend and eventually breaks

Question 28

thermal decompostion of group 1 nitrates

Answer 28

- apart for lithium, they dont fully decompose - produce a metla nitrite (NO2-) and O2 because they don;t have a big enough charge density - test for o2 by relighting a glowing split - as you go down group 1 its harder to decompose them so have to use more heat

Question 29

thermal decomposition of group 2 nitrates and lithium nitrates

Answer 29

- fully decompose - products are metal oxide, oxygen gas and nitrogen dioxide gas - nitrogen dioxide gas is brown and dangerous so experiemnts carried out in a fume cupboard - X(NO3)2 -(heat)-> XO + 1/2 O2 + 2NO2 - lithium also undergoes this because it is small so has a high charge density

Question 30

why does the thermal stability increae down groups 1 and 2

Answer 30

- more heat is needed to break down the carbonate and nitrate ions - The smaller positive ions at the top of the groups will polarise the anions more than the larger ions at the bottom of the group - The small positive ion attracts the delocalised electrons in the carbonate ion towards itself - the higher the charge and the smaller the ion the higher the polarising power - the more polarised they are, the more likely they are to thermally decompose as the bonds in the carbonate and nitrate ions become weaker

Question 32

investigating thermal stability

Answer 32

Thermal stability is a measure of how resistant a compound is to heat. Substances with a low thermal stability will decompose readily on heating. There is a trend in the thermal stability of Group 1 and 2 carbonates. You will investigate the thermal stability of Group 2 carbonates to establish this trend. Method: · Add 2g of a metal carbonate directly into the bottom of a boiling tube. · Set up your apparatus as in the diagram below - you can place the test tube with 2cm3 of limewater in it in a test tube rack. · Start heating the end of the test tube on a blue, roaring flame and carefully observe how long it takes for the lime water to become cloudy. CAUTION: Remove the delivery tube from the limewater solution BEFORE you stop heating the test tube. · Using your observations determine the trend in thermal stability of the Group 2 carbonates.

Question 33

group 7 properties

Answer 33

- very reactive don't exist in nature as native elements - diatomic - only group with gas, liquid, solid at rtp

Question 34

physical properties of flourine

Answer 34

gas pale yellow

Question 35

physical properties of chlorine

Answer 35

gas pale green

Question 36

physical properties of bromine

Answer 36

liquid orange/brown

Question 37

physical properties of iodine

Answer 37

solid dark grey/purple vapours

Question 38

physical properties of astatine

Answer 38

solid black

Question 39

trend in reactivoty down group 7

Answer 39

- decreases - atomic radius increases - attraction of outer eelctrons to nucleus decreases - harder to gain electrons - react by gaining an electron ie reduced so good oxididsign agent

Question 40

trend in volatility down group 7

Answer 40

- Volatility refers to how easily a substance can evaporate (volatile substance will have a low boiling point) - Going down the group, the boiling point of the elements increases which means the volatility of the halogens decreases - fluorine is the most volatile and iodine the least volatile

Question 41

trend in electronegativity down group 7

Answer 41

- decreases down the group - Going down the group, the atomic radii of the elements increase which means that the outer shells get further away from the nucleus - more shielding so attraction between outer electron and nucleus decreases - The halogens’ ability to accept an electron (their oxidising power) therefore decreases going down the group

Question 42

trend in melting and boiling points

Answer 42

-halogens are simple molecular structures with weak London dispersion forces between the diatomic molecules caused by instantaneous dipole-induced dipole forces The more electrons there are in a molecule, the greater the instantaneous dipole-induced dipole forces Therefore, the larger the molecule the stronger the London dispersion forces between molecules This is why as you go down the group, it gets more difficult to separate the molecules and the melting and boiling points increase

Question 43

solubility of halogens in water

Answer 43

low solubility in water since non-polar covalent atoms chlorine - virtually colourless bromine - orange (or yellow) idoine - brown

Question 44

solubility of halogens in hexane

Answer 44

chlorine - virtually colourless bromine - orange idoine - violet

Question 45

reactions of group 7 with groups 1&2

Answer 45

- form metal halides - ionic solids - usally white - redox reaction - group 1 and 2 being oxidised and group 7 being reduced -

Question 46

reactiosn of chlorine with water

Answer 46

disproportionation reaction forms 2 acids - hydrochlauric acid and chloric acid Cl2 + H2O ---> HCl + HOCl reaction used for diinfection of water of rdinking or in pools

Question 47

reaction of chlorine with cold alkali

Answer 47

Cl2 + 2NaOH ---> NaCl + NaClO + H2O disproportionation - Cl2 oxidised and reduced this makes bleach - sodium chlorate(I) (NaClO) is an active ingredient in bleach

Question 47

reaction of chlorine with hot alkali

Answer 47

3Cl2 + 6NaOH --- 5NaCl + NaClO3 + 3H2O forms sodium chlorate(V) - used as bleach and weed killer disproportiaonation raction

Question 48

halogen and halide displacement

Answer 48

more rwactive halogn cna displace the less reactive one form one of its compounds

Question 49

chlorine vs bromide and iodide

Answer 49

chlorine vs bromide - chlorine doesn't displace so orange chlorine vs iodide - chlorine doesn't displace so violet

Question 49

bromine vs chloride and iodide

Answer 49

bromine