topic 4: inorganic chemistry and the periodic table Flashcards
down the group, what happens to the atomic radius of group 2 and why?
increases
because of the addition of electron shells
down the group, what happens to the ionisation energy of group 2 and why?
decreases
- extra shells aded means that there is more electron shielding so there is weaker nuclear attraction between the positive nucleus and negative outer electrons
- larger atomic radius so the outer electrons are also further from the nucleus which weakens nuclear attraction
- easier to remove the outer electron so less energy is needed
down the group, what happens to the reactivity of group 2 and why?
increases
increased electron shielding and atomic radius makes the outer electrons easier to lose therefore reactivity increases
what is formed when group 2 metals react with chlorine?
down the group why do the reactions become more vigorous?
- metal chlorides (white precipitates)
-> e.g Mg + Cl2 -> MgCl2 - the elements are more reactive (increased electron shielding and atomic radius makes the outer electrons easier to lose therefore reactivity increases)
what is formed when group 2 metals react with water?
down the group why do the reactions become more vigorous?
If Mg reacts slowly with water, how can the reaction be sped up?
- forms metal hydroxides (base) which form an alkaline solution
-> Mg + 2H2O -> Mg(OH)2 +H2 - the elements are more reactive (increased electron shielding and atomic radius makes the outer electrons easier to lose therefore reactivity increases)
- reaction of Mg and water is faster using steam as it provides the reaction with extra energy
what is formed when group 2 metals react with oxygen?
strontium and barium can react oxygen and heat energy to form?
- forms oxides
e.g 2Mg + O2 -> 2MgO - metal peroxides
M (metal)
M + O2 -> MO2
how are alkaline solutions formed when group 2 metals are added to water?
- oxides react readily with water to make hydoxides which dissociate to form OH- ions
- becomes more strongly alkaline as we go down the group as the hydroxides become more soluble
what happens when group 2 reacts with dilute acids?
metal compounds + hydrogen gas
what forms when group 2 hydroxides react with dilute acid?
- forms salt and water (neutralisation reaction)
HCl: chloride salt
sulfuric acid: sulfate salt
nitric acid: nitrate salts
down the group, why does the solubility of group 2 hydroxides increase?
the ionic size of the metal ions increases. Larger ions have weaker attractive forces and lower lattice energies. The decrease in lattice energy makes it easier for the larger hydroxide compounds to dissolve in water
Larger metal ions in Group 2 elements have a lower charge density, making them more easily surrounded by water molecules. This process of hydration releases energy, known as hydration energy. The increase in the number of water molecules surrounding larger ions leads to a more stable and soluble complex in solution.
down the group, why do group 2 sulphates decrease in solubility
the ionic size of the metal ions increases. Larger ions have weaker attractive forces between them and the water molecules in solution. This decrease in attraction makes it more difficult for the larger ions to be fully surrounded by water molecules and consequently reduces their solubility.
the lattice energy decreases because the larger ions have a lower charge density and weaker attraction, resulting in a less stable lattice. With a weaker lattice, the sulfates are less likely to dissolve readily in water
what is thermal decomposition?
the breakdown of a compound into simpler substancesvia heat
after undergoing thermal decomposition, group 2 carbonates produce
metal oxide + carbon dioxide
e.g XCO3 -> XO + CO2
after undergoing thermal decomposition, group 2 nitrates produce
powdered metal oxide + nitrogen dioxide (brown gas) + oxygen
2X(NO3)2 -> @XO + 4NO2 + O2
what happens for group 1 during thermal decomposition?
lithium acts in the same way as group 2 nitrates and carbonates
group 1 nitrates produce a metal nitrite and oxygen
group 1 carbonates will not decompose upon heating in a lab as extremely high temperatures are required
why does thermal stability increase down both nitrate and carbonate groups
down the group, the larger metal cations have weaker interaction with the other anion and have less polarising power, distorting the bond in the electron cloud less
what is the flame test procedure?
- dip a clean nichrome wire loop into fresh concentrated HCL to clean
- heat wire on the edge of a blue flame of a bunsen burner until no colour is produced
- dip wire into solid sample
- observe colour of flame
in a flame test, why does the wire have to be made of nichrome of platinum?
these materials are inert, stable, unreactive and produce no colour when heated in the flame
in a flame test, why does the wire have to be cleaned?
to remove residue of any previous sample being tested
in a flame test why does the HCL have to be fresh and concentrated?
fresh - so there are no contaminants of residue from previous tests which will lad to incorrect results
concentrated - enables the solid salt to become attached to the wire
explain the flame test in terms of its electrons
- the heat from the flame provides thermal energy to the atoms, absorbed by the electrons in the metal ions, causing them to jump from their ground state (lower energy level) to higher energy levels and become excited
- return to their original energy levels (ground state), they release the excess energy they gained in the form of photons (light). This emitted light corresponds to specific wavelengths that are characteristic of the metal ion present in the sample
what are the colours of group 1 in the flame test
lithium - red
sodium - orange/yellow
potassium - lilac ( use blue glass)
what are the colours of group 2 in the flame test?
magnesium - colourless (white light emitted)
calcium - brick red
strontium - crimson red
barium - apple green
how to test for the inorganic substance: ammonium (NH4+) (basic gas)
add dilute NaOh and warm gently, test gas evolved with damp red litmus paper
positive: red litmus paper turns blue
how to test for the inorganic substance:
iron (II) ion (Fe2+)
add dilute NaOH dropwise to excess
positive: green precipitate then change to rust brown precipitate when standing in air, does not dissolve in excess NaOH
how to test for the inorganic substance:
Iron (III) ion (Fe3+)
add dilute NaOH dropwise to excess
positive: rust brown precipitate, doesnt dissolve in excess NaOH
how to test for inorganic substance:
copper ion (Cu2+)
add dilute ammonia solution dropwise to excess
positive: dark blue precipitate, dissolves in excess ammonia
how to test for inorganic substance:
sulphate (SO4 2-)
add dilute HCL acid ( eliminates carbonate, the unwanted ion, and ensures the product is only BaSO4) and warm gently
add 3 drops of barium chloride
positive:
white precipitate formed
how to test for inorganic substance:
carbonate (CO3 2-)
add dilute HCL and warm gently, test gas evolved with limewater
positive: limewater turns milky
how to test for inorganic substance:
chloride (cl-)
add an equal volume of dilute nitric acid, ass 3 drops of silver nitrate solution
precipitate should form, add excess ammonia
positive: white precipitate that dissolves in dilute ammonia
how to test for inorganic substance:
bromide (Br-)
add an equal volume of dilute nitric acid, ass 3 drops of silver nitrate solution
precipitate should form, add excess ammonia
positive: creamy precipitate only soluble in concentrated ammonia
how to test for inorganic substance:
iodide (I-)
add an equal volume of dilute nitric acid, ass 3 drops of silver nitrate solution
precipitate should form, add excess ammonia
positive: yellow precipitate that is insoluble in concentrated ammonia
how to test for inorganic substance:
halides
solid halides react differently with concentrated sulfuric acid
positive:
NaCl: white fumes, white solid
NaBr: white fumes, orange vapour, white solid
NaI: dark solid formed with purple vapour, yellow solid, bad egg smell
how to test for inorganic substance:
iodine (I2)
add starch or cyclohexane
positive:
starch: solution goes blue/black
cyclohexane: cyclohexane layer becomes purple
what are the colours and states (RTP) of the halogens?
F2: yellow, gas
Cl2: pale green, gas
Br2: red/brown, liquid
I2: grey, solid
why does melting and boiling point increase down the group in group 7?
more electrons and an increase in electron shells, meaning the london forces between the halogen molecules get stronger and are easily able to introduce temporary dipoles, more force needed to overcome london forces
why does reactivity decrease down the group in group 7?
atoms get larger down the group so the outer electron in the p shell get further away from the nucleus -> more shielding and less nuclear attraction meaning it is harder to gain an electron
reactivity decreases
why do atomic radius and ionic radius increase down the group in group 7?
atomic r: greater atomic number, more electrons and more shells
ionic r: the number of electron orbitals increases in number moving into higher and higher periods
why does electronegativity decrease down the group
although there is an increasing nuclear charge due to greater number of protons, there is an increasing number of shells -> more shielding and less pull on electrons
increasing atomic radius -> attraction drops off as distance increases
nucleus is less able to attract the bonding pair of electrons towards itself
what is a displacement reaction?
a more reactive halogen will displace a less reaction one from its halide salt
solution of halogen and water is added to a solution with halide mix (colourless)
cl > br > i
what is the general reaction of a halogen and cold dilute alkali solution?
what happens in the disproportion reaction?
X^2 + 2NaOH -> NaOX + NaX + H2O
halogen oxidation numbers:
0 -> +1 -1
what is the general reaction of a halogen and hot dilute alkali solution?
what happens in the disproportion reaction?
3X^2 + 6NaOH -> NaXO^3 + 5NaX + 3H2O
halogen oxidation numbers:
0 -> +5 -1
what is the order of reducing power of the halides from strongest to weakest?
iodide (I-)
Bromide
Chloride
what is the explanation for the order of the reducing power of halides?
they have a greater tendency to donate electrons
As the ionic radius increases, it is easier for the outer electrons to be given away, and the pull from the nucleus decreases
