4 - Inorganic chemistry and the periodic table Flashcards
Trend in ionisation energy down group 2?
- decreases as you go down the group
- atomic radii increases
- number of shells increases, greater shielding effect.
- energy of the outermost electrons increases,
- so ionisation energy decreases down a group.
What type of bonding is present in group 1 and 2 elements?
metallic bonding
Trend in metallic bonding down group 1 and 2?
- decreases
- although nuclear charge increases
- atomic radius increases
- distance between the positive nuclei and delocalised electrons increases.
- shielding effect from inner electron shells also increases
- force of attraction between positive nuclei and delocalised electrons decreases.
Trend in reactivity down group 2?
- increases
- although nuclear charge increases
- atomic radii increases
- shielding effect increases
- attraction between nucleus and outer electrons decreases.
- easier to remove outer electrons, easier to form cations.
group 2 metal + oxygen
metal oxide.
- bright flame
- high melting points (ionic bonding)
2M + O2 -> 2MO
Group 2 metal + chlorine
metal chloride
- misty fumes
- white solid
M + Cl2 -> MCl2
Group 2 metal + water (warm)
metal hydroxide
- bubbles form
- fizzing
- metal dissolving
- solution heats up
^^(more vigorous, faster, more heat, down the group due to increase in reactivity).
- calcium, white precipitate. (Less precipitate forms down the group)
M + 2H2O(l) -> M(OH)2(aq) + H2
Calcium is exception:
Ca + 2H2O(l) -> Ca(OH)2(s) + H2
calcium hydroxide is only slightly soluble in water, precipitate forms, solution becomes cloudy.
Group 2 metal + water (steam)
metal oxide and hydrogen
- bright flame
M + H2O(g) -> MO(s) + H2
What type of reactant is a metal oxide classified?
Base
Group 2 oxide + water
metal hydroxide
MO(s) + H2O(l) -> M(OH)2(aq)
simplified (no change in Mg2+ ion):
O2- + H2O -> 2OH-
What type of reaction occurs when group 2 oxides AND hydroxides react with dilute acids?
BAWS
- neutralisation reaction.
MO + H2SO4 -> MSO4 + H2O
M(OH)2 + H2SO4 -> MSO4 + 2H2O
M(OH)2 + 2HCl -> MCl2 + 2H2O
Trend in solubility of group 2 sulfates down the group?
- decreases down the group.
- magnesium sulfate soluble
- calcium sulfate slightly soluble
- strontium and barium sulfate insoluble.
How is the insolubility of a certain group 2 sulfate used to test for the presence of sulfate ions?
- sample solution is acidified with dilute hydrochloric acid (to remove carbonate impurities).
- barium chloride solution is added.
- If sulfate ions are present, the sulfate ions in the solution will react with the barium ions in the BaCl2 to form BaSO4. BaSO4 is insoluble and will show as a white precipitate.
Trends in solubility of group 2 hydroxides down the group?
- increases down the group.
- magnesium hydroxide has very low solubility in water.
- barium hydroxide has high solubility in water.
What is the formula for limewater?
Calcium hydroxide
Ca(OH)2.
reasonably soluble in water.
What is the test for CO2?
- lime water is used.
- CO2 reacts to form CaCO3 which is a white precipitate.
- CaCO3 is insoluble in water
- limewater turns cloudy.
Trend in thermal stability of group 1 and 2 carbonates and nitrates down the group?
- thermal stability increases down the group.
- cation size increases
- polarising ability of the cation on the anion decreases.
- bond strength increases between cations and anions.
- thermal stability increases
Do group 1 carbonates decompose?
No, except lithium carbonate.
- group 1 cations have a 1+ charge which means that the polarising ability of group 1 cations are too small.
- Lithium ion is small enough to have a polarising ability on the carbonate anion.
- group 1 carbonates are all thermally stable except lithium.
Polarising effect compare between group 1 and group 2 cations
group 2 cations have a greater polarising effect because they have a 2+ charge.
the 1+ charge on the group 1 ions means they have a too little charge density to have a polarising ability. (group 1 carbonates cannot decompose except lithium).
What is polarising ability of a cation?
The ability of a cation to distort the electron cloud around the anion.
What factors affect polarising ability?
- size of cation charge
- size of cation
decomposition of lithium carbonate?
Li2CO3(s) -> Li2O(s) + CO2(g)
- test with limewater (turns cloudy) to see if it has decomposed.
What do group 2 nitrates decompose to?
- oxide
- nitrogen dioxide
- oxygen
What do group 1 nitrates decompose to?
Only lithium nitrate:
- oxide
- nitrogen dioxide
- oxygen
other group 1 nitrates:
- nitrite (III)
- oxygen
What colour is NO2 gas?
- brown gas.
what is the formula for nitrate (v)?
NO3-
what is the formula for nitrate (III)?
NO2-
Group 1 ion colours?
- Li+ : red
- Na+ : yellow/orange
- K+ : lilac
- Rb+ : red/purple
Cs+ : blue/violet
Group 2 ion colours?
- Mg2+ : no colour
- Ca2+ : brick red
- Sr2+ : crimson red
- Ba2+ : apple green
What does lithium and group 2 carbonates decompose to?
metal oxide and carbon dioxide
Why does a colour show in a flame test?
- electrons absorb energy from the Bunsen flame and move to higher energy levels.
- ground state to excited state.
- the electrons immediately fall back to their ground state, releasing energy.
- if this energy corresponds to radiation in the visible part of the electromagnetic spectrum, a colour is seen.
Steps of a flame test?
- use a nichrome wire
- clean it by dipping in concentrated hydrochloric acid and heat in Bunsen flame.
- dip clean nichrome wire in solid and put in Bunsen flame.
States of group 7 elements at room temp?
- fluorine: gas
- chlorine: gas
- bromine: liquid
- iodine: solid
- astatine: solid
trend in electronegativity down group 7?
- decreases
- because atomic radius increases due to increasing number of electron shells.
- nucleus is further away from bonding pair of electrons (distance increases), and shielding effect from inner electron shells increases.
Trend in melting/boiling temperatures down group 7?
- increases
- number of electrons increases
- stronger London forces between the halogen molecules.
Trend in reactivity down group 7?
- reactivity decreases down the group
- although nuclear charge increases
- atomic radii increases
- number of shells increases
- shielding effect from inner shells increases.
- so as you go down the group halogen atoms will less easily attract and accept electrons.
Reaction of group 1 and 2 metals with halogens? and what type of reaction is this?
- forms salts (metal halides). usually white solids.
- oxidation reaction.
halogen and halide displacement reactions. What displaces what?
displacement reactions are redox reactions
A more reactive halogen displaces a less reactive halogen from one of its compounds.
reactivity: chlorine > bromine > iodine
- chlorine displaces both bromine and iodine
- bromine displaces iodine (not chlorine)
- iodine does not displace either chlorine or bromine (least reactive out of the three).
- occurs in aqueous solution
observations of halogens in aqueous solution?
- chlorine: colourless
- bromine: orange/brown
- iodine: red
Why are organic solvents added to halogen halide displacement reactions and observations?
- usually cyclohexane
- halogens are more soluble in cyclohexane (organic solvent) than in water.
- when added to the aqueous solution,
- halogen dissolves in the organic upper layer, where the colours can be more clearly seen.
in organic solvent:
- chlorine: very pale green
- bromine: orange/brown
- iodine: violet
What is a disproportionation reaction?
It is a reaction where the same element is simultaneously oxidised and reduced.
Reaction of Cl2 and water? And what type of reaction is this?
- forms chlorine water and
- disproportionation reaction
- Cl2 + H2O -> HCl + HClO
- chlorine is reduced and oxidised.
- chlorine dissolved in water kills pathogens in water.
Reaction of Cl2 and cold dilute aqueous NaOH solution? And what type of reaction is this?
- forms bleach
- disproportionation
Cl2(aq) + 2NaOH(aq) -> NaCl(aq) + NaClO(aq) + H2O(l) - sodium chlorate (I) - bleach.
Reaction of Cl2 and hot concentrated NaOH solution? And what type of reaction is this?
- substance used in bleaching and as a weed killer.
- disproportionation
3Cl2(aq) + 6NaOH(aq) -> 5NaCl(aq) + NaClO3(aq) + 3H2O(l) - sodium chlorate (V) - bleach, weed killer.
What do you do if asked to predict reactions of fluorine and astatine?
treat like the other halogens learnt in this topic.
e.g sodium + iodine -> sodium iodide
sodium + astatine -> sodium astatate (NaAt)
How to test for CO3- ions?
- add any dilute strong acid to sample solution
- fizzing will be seen due to CO2 produced.
- indicates that carbonate ions are present.
2HCl + Na2CO3 -> 2NaCl + H2O + CO2
2H+ + CO32- -> H2O + CO2
How to test for CO2?
- bubble gas through limewater
- limewater turns cloudy
- due to calcium carbonate precipitate formed.
How to test for SO42-?
- add dilute hydrochloric acid (to remove carbonate impurities).
- add barium chloride solution
- If sulphate ions are present, they react with the barium ions to produce barium sulphate.
- barium sulphate is insoluble in water and will form a dense white precipitate.
How do you test for NH4+?
- add warm aqueous sodium hydroxide
- ammonia NH3 is formed.
- can be identified by pungent smell, damp red litmus paper turns blue.
Test for halide ions?
- add dilute nitric acid (to remove any other anions)
- add silver nitrate solution
- cl-: silver nitrate
- silver bromide
- silver iodide
Add ammonia solution
- AgCl: dissolves in ammonia solution to give colourless solution
- AgBr: insoluble in dilute ammonia solution, dissolves in concentrated ammonia solution.
- AgI: insoluble in ammonia solution of any concentration.
Test for hydrogen halide?
- add ammonia gas
NH3(g) + HX(g) -> NH4X(g) - white fumes produced.
- turns blue litmus paper red.
