Topic 4 Inorganic chemistry and the periodic table Flashcards
Atomic radius in group 2
The atomic radius increases as we go down Group 2. This is as extra shells are added as you go down
All group 2 metals lose 2 electrons to form +2 ions when they react.
All group 2 metals have electron configurations that end in s2
Ionisation Energy in Group 2
1st IE decreases as we go down group 2. There is more shielding hence weaker attraction between the nucleus and outer electrons. The outer electrons are also further from the nucleus which weakens the attraction.
We do have an increase in the number of protons as we go down the group. However, the shielding effect overrides an increase in + charge
Group 2 reaction with water
React with water to form metal hydroxides
Sr(s) + 2H2O(l) —–> Sr(OH)2(aq) + H2(g)
Reactivity increases with water as you go down the group. (There is no reaction with Be)
The reason why is that the atom gets larger and the electron is further from the nucleus. Easier to remove and hence more reactive. There is more shielding
Magnesium reacts slowly with cold water but more rigorously with steam. This produces Magnesium Oxide(MgO) instead of hydroxide
Group 2 reaction with oxygen
They react with oxygen to form metal oxides
2Mg(s) + O2(g) —–> 2MgO(s)
The oxidation number of Mg increases from 0 to +2. Magnesium is being oxidised
The oxidation number of O decreases from 0 to -2. Oxygen is being reduced
Group 2 oxides are white solids
Group 2 reaction with chlorine
They react with chlorine to form metal chlorides.
Mg(s) + Cl2(g) —-> MgCl2(s)
The oxidation number of Mg increases from 0 to +2. Magnesium is being oxidised
The oxidation number of chlorine has been reduced from 0 to -1. Chlorine is being reduced.
Group 2 oxides reaction with water
They react with water to form bases. Alkaline solutions formed.
SrO(s) + H2O(l) —-> Sr(OH)2(aq)
SrO(s) + H2O9l) —-> Sr2+(aq) + 2OH-(aq)
Oxides react readily with water to make hydroxides which dissociate to form OH- ions. (Magnesium oxide reacts very slowly and the hydroxide barely dissolves. Beryllium oxide doesn’t react with water at all and the hydroxide is insoluble)
They become more strongly alkaline as we go down the group as the hydroxides become more soluble
Group 2 oxides and hydroxides neutralisation
They can neutralise acids
How oxides react with acids : Cao(s) + 2HCl(aq) —-> CaCl2(aq) + H2O(l)
How hydroxides react with acids : Ca(OH)2(s) + 2HCl(aq) —> CaCl2(aq) + 2H2O(l)
Group 2 compounds solubility
As a general rule, if the -ion has a double charge, they become less soluble as we go down a group
Generally, if the - ion has a single - charge they become more soluble down the group
Group 2 compounds decomposition
Group 2 carbonates and nitrates can decompose upon heating
Carbonates break down into metal oxides and carbon dioxide. This is via thermal decomposition
CaCO3(s) —-> CaO(s) + Co2(g)
Nitrates break down into metal oxides, nitrogen dioxide and oxygen via thermal decomposition
2Ca(No3)2(s) —> 2CaO(s) +4NO2(g) + O2
Carbonates/Nitrates become more thermally stable as we go down group 2.
The carbonate/nitrate ion has a large electron cloud that can be distorted when nearby + group 2 metal ions
All group 2 metal ions have a +2 charge however they become larger as we go down the group meaning the charge is spread out over a larger area. They have a lower charge density
Mg2+ has a high charge density and distorts the electron cloud in carbonates/nitrates ions more than Ba2+ which has a lower charge density. The less distortion the more stable the carbonate is.
Group 1 compounds decomposition
Group 1 carbonates can also decompose upon heating and are more thermally stable than group 2 compounds.
Carbonates are thermally stable under a Bunsen flame. Except for lithium carbonate which forms an oxide and CO2. Lo2Co3(s) —-> Li2O(s) + CO2(g)
Nitrates break down nitrites and oxygen (except LiNO3 decomposes to form Li2O + NO2+ O2)
2KNO3(s) —-> 2KNO2(s) + O2(g)
No3- is a Nitrate ion
NO2- is a nitrite ion
Testing thermal stability of nitrates and carbonates
Nitrates:
Measure how long it takes a specific amount of oxygen to be produced. Using a gas syringe or the amount needed to relight a glowing splint
The length of time it takes to produce a specific amount of NO2. It is a brown gas so it can be easily observed. It is toxic so it must be done in a fume cupboard
Carbonates:
The length of time it takes until a specific amount of CO2 is produced. Co2 turns limewater cloudy so the quicker this turns cloudy the more carbon dioxide is produced. Could use a gas syringe too.
Flame test - How do we get different colours?
Test for + ions (cations) in a compound using flame tests
Electrons in the shells move to higher energy levels as they absorb energy from the flame. When they drop back down to lower energy levels light is released. Different colours are produced as the difference in energy levels determines the wavelength of light released.
Flame test - Method and colours
Dip the nichrome wire in concentrated HCl. Dip into the sample. Place the loop into the blue flame and observe the colour
Calcium - Dark red
Rubidium - Red
Lithium - Crimson
Strontium - Crimson
Sodium - Yellow-orange
Barium - Green
Caesium - Blue
Potassium - Lilac
The Halogens - Group 7
They make up group 7
Fluorine is a pale yellow gas
Chlorine is a pale green gas
Bromine is a brown-orange liquid
Iodine is a grey solid
The Boiling points increase as we go down the group. This is because the London forces increase due to increasing size and relative mass of the atoms.
The physical state goes from gas at the top of group 7 to solid at the bottom
Electronegativity decreases as we go down the group. Electronegativity is the ability for an atom to attract electrons towards itself in a covalent bond. The atom gets larger and the distance between the + nucleus and bonding electrons increases. There is also more shielding
Displacement reaction
Adding hexane can make it easier to observe colour changes.
When undertaking halogen displacement reactions we can add an organic solvent like hexane to see the colour change easily
TOBA
The halogen present will dissolve readily in the organic solvent which forms a layer above the aqueous layer. A coloured band will appear. Organic is on top of aqueous
More reactive halogen will displace less reactive halide ions
Reactivity in halogens decreases as we go down group 7. For a reaction to occur an electron is gained. Atoms with a smaller radius attract electrons better than larger atoms. Halogens are less oxidising as we go down the group. We can show this by reacting halogens with halide ions
