topic 4 - inorganic chemistry and the periodic table Flashcards
what’s the ionization energy trend for group 2
- ionization energy decreases down the group
- each element going down has an extra electron shell
- more shielding
- valence electrons further from the nucleus which reduces the electrostatic force of attraction
increased positive charge ( extra protons ) is overridden by the effect of shielding - making it easier to remove outer electrons
- hence why reactivity increases going down the group
what is produced when group 2 elements react with water
metal hydroxide + hydrogen
what is produced when a group 2 metal is burnt in oxygen
solid white oxides
what happens when a group 2 metal reacts with chlorine
solid white chlorides
what is the reactivity of group 2 metals with water and what are the exceptions
- metals react readily with water to form metal hydroxides , which dissolve
- the hydroxide ions, OH- make these solutions strongly alkaline
- beryllium oxide is an exception because it doesn’t react with water and berillyium hydroxide is insoluble
- magnesium oxide is another exception because it only reacts slowly and hydroxide isn’t very soluble
what’s the difference between alkalis and bases
bases are insoluble in water. on the other hand, alkali produces ions when dissolving in water
what’s the trends for oxides pH going down group 2
the oxides form more strongly alkaline solutions going down the group because the hydroxides get more soluble
what does it mean that group 2 oxides and hydroxides are bases
they will neutralise dilute acids forming solutions of the corresponding salts
magnesium oxides reaction with water
MgO(s) + H2O (l) —> Mg(OH)2 (aq)
magnesium hydroxide reaction with water
Mg(OH)2(s) + H2O(l) —> Mg(OH)2(aq)
magnesium oxide reaction with dilute acid
MgO(s) + 2HCl(aq) —> MgCl2(aq) +H2O(l)
magnesium hydroxide reaction with dilute acid
Mg(OH)2(aq) + 2HCl(aq) —> MgCl2(aq) + 2H2O(l)
what does solubility trend in a group depend on and what are the trends in group 2
the compound anion
- group 2 elements that contain singly charged negative ions ( e.g. OH-) **increase **solubility
- compound that contain doubly charged negative ions decrease in solubility down the group
what is the exception for solubility in group 2
most sulfates are soluble in water but barium sulfate is insoluble
what does sparingly soluble mean?
compounds like magnesium hydroxide that have very low solubility
what does thermal decomposition mean
thermal decomposition is when a substance breaks down ( decomposes ) when heated
- the more thermally stable a substance is, the more heat it will take to break it down
what’s a trend of thermal stability down a group ( carbonates and nitrates )
- thermal stability increases down a group
- the carbonate and nitrate ion and large negative ions ( anions ) and can be made unstable by the presence of a positively charged ion ( a cation )
- the cation polarises the anion, distorting it. the greater the distortion, the less stable the compound
- large cations cause less distortion than small cations as they have a lower charge density. so the further down the group, the larger the cations, the lower the charge density so the less distortion caused and the more stable the carbonate/nitrates compound
what does it mean to have a lower charge density
the charge on the ion is spread out over a larger area
what’s the difference in thermal stability in group 2 and group 1
group 2 compounds are less thermally stable than group 1 compounds
- the greater the charge on the cation, the greater the distortion and the less stable the carbonate/ nitrate ion becomes. group 2 cations have a +2 charge, compared to a +1 charge for group 1 cations so group 2 carbonates and nitrates are less stable than those of group 1
how do group 1 carbonates decompose and what is the exception
group 1 carbonates are thermally stable so you can’t heat them enough with a bunsen burner to make them decompose ( they do compose at higher temperatures )
- except Li2CO3 which decomposes to Li2O and CO2
how do group 1 nitrates decompose
to form nitrite and oxygen
2MNO3 (s) —> 2MNO2(s) + O2 (g)
- except LiNO3 which decomposes to form Li2O, NO2, and O2
how do group 2 carbonates decompose
to form the oxide and carbon dioxide
MCO3(s) —> MO(s) + CO2(g)
how does group 2 nitrates decompose
form the oxide, nitrogen dioxide and oxygen
2M(NO3)2 (s) —> 2MO(s) + 4NO2 (g) + O2 (g)
how to test how easily nitrates decompose
- how long it takes until a certain amount of oxygen is produced ( i.e. enough to relight a glowing splint )
- how long it takes until an amount of brown gas ( NO2 ) is produced. this needs to be down in a fume cupboard because NO2 is toxic
how to test how easily carbonates decompose
how long it takes for an amount of carbon dioxide to be produced. you test for carbon dioxide using lime water - which is a saturated solution calcium hydroxide. this turns cloudy with carbon dioxide
how to do a flame test
1) mix a small amount of the compound you are testing with a few drops of hydrochloric acid
2) heat a piece of platinum or nichrome wire in a hot bunsen flame to clean it
3) dip the wire into the compound/acid mixture. hold it in a very hot flame and note the colour produced
what colour does lithium produce in a flame test
red
what colour does sodium produce in a flame test
orange/yellow
what colour does potassium produce in a flame test
lilac
what colour does rubidium produce in a flame test
red
what colour does caesium produce in a flame test
blue
what colour does calcium produce in a flame test
brick red
what colour does strontium produce in a flame test
crimson
what colour does barium produce in a flame test
green
how does a flame test produce colour
the energy absorbed from the flame causes electrons to move to a higher energy level. the colours are seen as the electrons fall back down to lower energy levels, releasing energy in the form of light.
the difference in energy between the higher and lower levels determines the wavelength of the light released - which determines the colour of the light
what is the trend for electronegativity in halogens
decreases down the group
what are the properties of fluorine
pale yellow, gas
what are the properties of chlorine
green, gas
what are the properties of bromine
red- brown , liquid
what are the properties of iodine
grey , solid
what’s the solubility of halogens
in their natural state they exist as covalent diatomic molecules. because they are non polar they have low solubility in water. ( but they dissolve easily in organic compounds like hexane )
iodine is insoluble in both dilute and concentrated
chlorine is soluble in both dilute and concentrated
bromine is insoluble in dilute but soluble in concentrated
what colour does chlorine produce in water and hexane
virtually colourless in both
what colour does bromine produce in water and hexane
yellow/ orange in water and orange/ red in hexane
what colour does iodine produce in water and hexane
brown in water and purple in hexane
what is the reactivity trend for halogens
decreases going down the group
gain electrons so are oxidizing agents
- atoms become larger
- greater distance from nucleus
- more shielding
- harder to gain electrons
what is the halogen trends in electronegativity
decreases down group 7 due to the increase in number of electron shells and increase in distance between the nucleus and the bonding electrons
what is the trends for melting and boiling points for halogens
increase going down the group
- increase in electron shells
- stronger london forces between the molecules
- this makes it harder to overcome the intermolecular forces
why is fluorine and astatine hard to study
fluorine is a toxic gas and astatine is highly radioactive and decays quickly
how can you see halogens relative oxidizing strength
can be seen in their displacement reaction with halide
- chlorine will displace both bromide and iodide ions
- bromine will displace iodide but not chloride ions
- iodine will not displace chloride or bromide ions
what is the displacement reaction between halides
redox reaction
thing being displaced is oxidized and the thing that does the displacing is reduced
half equations:
Cl2 + 2e- —> 2Cl-
2Br - —> Br2 +2e-
(chlorine displaced bromine)
reaction of potassium chloride (colourless) with chlorine water ( colourless ), bromine water (orange) and iodine solution ( brown )
no reaction in all
reaction of potassium bromide (colourless) with chlorine water ( colourless ), bromine water (orange) and iodine solution ( brown )
chlorine = Cl2+2Br- —> 2Cl- +Br2 (aq)
—> mixture will turn orange
bromine and iodine = no reaction
reaction of potassium iodide (colourless) with chlorine water ( colourless ), bromine water (orange) and iodine solution ( brown )
chlorine = Cl2 + 2I- —> 2Cl- + I2
—> turns orange
bromine = Br2 + 2I- —> 2Br- +I2
—> turns brown
iodine = no reaction
how to make colour change easier to see ( halogen displacement reaction )
shake the reaction with an organic solvent like hexane
- the halogen present will dissolve in the organic solvent which settles out as a distinct layer above the aqueous solution
equations for halogens disproportionation reaction with cold alkalis
X2 + + 2NaOH —> NAOX + H2O
ionic equation :
X2 + 2OH- —> OX- + X- + H2O
how to produce bleach with equation
mix chlorine gas with cold, dilute aqueous sodium hydroxide —> sodium chlorate (I) solution ( bleach )
2NaOH (aq) + Cl2 (g) —> NaClO(aq) +H2O (l)
3 uses of bleach
- water treatment
- bleach paper and textiles
- cleaning
equations for halogens disproportionation reaction with hot alkalis
3X2 + 6NaOH —> NaXO3 + 5NaX + 3H2O
ionic equation
3X2 + 6OH- —> XO3- + 5X- + 3H2O
what happens when you mix chlorine with water
it undergoes disproportionation
end up with a mixture of hydrochloric acid and hypochlorous acid
Cl2(g)+ H2O(l) —> HCl (aq) + HClO (aq)
<—
how can hypochlorous acid be used to kill bacteria
hypochlorous acid ionizes to make chlorate (I) ions ( also called hypochlorite ions )
HClO (aq) + H2O (l) —> ClO- (aq) +H3O(aq)
<—
chlorite (I) ions kill bacteria
what happens when halogens react
they are reduced , the oxidize other substances
oxidize group 1 and 2 to produce halide salts
equation and half equation of lithium reacting to fluorine ( group 1 + halide )
2Li(s) + F2 (g) — 2LiF (s)
Li : +1 oxidised - Li —> Li+ + e-
F : -1 reduced - F2 + 2e- —> 2F-
equation and half equation of magnesium reacting to chlorine ( group 2 + halide )
Mg(s) + Cl2 (g) —> MgCl2 (s)
Mg : +2 oxidised - Mg —> Mg2+ + 2e-
Cl : -1 reduced - Cl2 + 2e- —> 2Cl-
what is the trend of the reducing power of halides
halide ion can act as a reducing agent by losing an electron
decreases down the group
- ions get bigger so electrons are further away
- shielding weaker force of attraction
reaction of halides and concentrated sulfuric acid
hydrogen halide
features of hydrogen halides
- colourless gases
- can dissolve in water
- produce misty fumes of acidic gas
- turn blue litmus paper red
- react with ammonia to give white fumes
how to test for halides
- add dilute nitric acid
- add silver nitrate solution
- observe precipitate colour
what colour precipitate does fluoride ions form when reacted to nitric acid and silver nitrate
no precipitate
what colour precipitate does chloride ions form when reacted to nitric acid and silver nitrate
white
what colour precipitate does bromide ions form when reacted to nitric acid and silver nitrate
cream
what colour precipitate does iodide ions form when reacted to nitric acid and silver nitrate
yellow
why add ammonia after halide test
to make it easier to identity colour
- AgCl —> dissolves and gives a colourless solution
- AgBr —> remains unchanged if in dilute ammonia solution but will dissolve in concentrated ammonia solution to give a colourless solution
-AgI - doesn’t dissolve even in concentrated ammonia solution
how to test for carbonates and hydrogen carbonates
add hydrochloric acid
fizz and give off CO2
test for CO2 using limewater
( turn cloudy )
how to test for sulfates
add hydrochloric acid and barium chloride
- white precipitate formed
how to test for ammonium compounds
ammonia gas is alkaline so you can check for it using red damp litmus paper turning it blue
add sodium hydroxide and gently heat
if ammonia is given off ammonium ions is present
- fume cupboard
what does a reaction of a halide and concentrated sulfuric acid give
hydrogen halide
