Inorganic Chemistry and the Periodic Table Flashcards
Trends in atomic radius for group 2 elements
Group 2 elements form 2+ ions when they react
Atomic radius increases down the Group.
As one goes down the group, the atoms have more shells of electrons making the atom bigger.
What is a common name given to group 2 metals?
Alkaline earth metals
What is the most reactive metal of group 2?
Barium
List 3 physical properties of group 2 metals
● High melting and boiling points
● Low density metals
● Form colourless (white) compounds
The highest energy electrons of group 2 metals are in which subshell?
S subshell
Does reactivity increase or decrease down group 2? Why?
● Increases
● Electrons are lost more easily because larger atomic radius and more shielding.
What happens to the first ionisation energy as you go down group 2? Why?
1st ionisation energy decreases as we go down group 2
Extra shells added as we go down group 2
The outer electrons are further away from the nucleus
which weakens the attraction
There is more shielding, hence the attraction between the outermost electron and the nucleus decreases
This makes it easier to remove the outer electron, so less energy is required to remove it
What type of reaction is the reaction between group 2 elements and oxygen?
Redox reaction
Write an equation for the reaction of calcium and oxygen
2Ca (s) + O2 (g) → 2CaO (s)
What is the product when group 2 elements react with water?
Hydroxide and hydrogen gas
Which group 2 element doesn’t react with water?
Beryllium
Which group 2 element reacts very slowly with water?
Magnesium
What type of reaction is the reaction between group 2 metal and water?
Redox reaction
Write an equation for the reaction of Barium and water
Ba (s) + 2H2O (l) → Ba(OH)₂ (aq) + H₂ (g)
What is oxidised and what is reduced in a reaction between group 2 metal and water?
Metal → oxidised
One hydrogen atom from each water → reduced
What are the products when group 2 oxide reacts with dilute acid?
Salt and water
Write an equation for the reaction of calcium and hydrochloric acid
CaO (s) + 2HCl (aq) → CaCl2(s) + H₂O (l)
What is formed when group 2 oxides react with water?
Metal hydroxide
Write an equation for the reaction between a group 2 oxide and water
MO (s) + H2O (l) → M(OH)2 (aq)
Which group 2 metal oxide is insoluble in water?
Beryllium oxide
Write an equation for the reaction between Mg(OH)2 and nitric acid
2HNO3 (aq) + Mg(OH)2 (aq) Mg(NO3)2 (aq) + 2H2O (l)
What is the trend in hydroxide solubility down group 2?
Increases down the group
Mg(OH)₂ is slightly soluble
Ba(OH)₂ creates a strong alkaline solution
What is the trend in sulphate solubility down group 2?
Group 2 sulphates become less soluble down the group with BaSO4 being the least soluble.
Explain the reasons for the trend of thermal stability in group 1 and 2 carbonates
Group 2 carbonates are more thermally stable as you go down the group. This is because the cations get bigger so therefore have less of a polarising effect distorting the carbonate ion less. As C-O bond is not weakened as much it harder to break down
Group 1 carbonates do not decompose except for lithium. This is because they don’t have a big enough charge density to polarise the carbonate ion as they only form 1+ ions. However Lithium ion is small enough to have a polarising effect so therefore lithium carbonate can decompose.
Explain the reasons for the trend of thermal stability in group 1 and 2 nitrates
The ease of thermal decomposition decreases down group 2 and this is because down the group the ions get larger and therefore has less charge density = less polarisation of nitrate anion and less weakening of the N―O bond.
Group 1 nitrate do not decompose with the exception of Lithium nitrate. Lithium ion is smaller enough to charge polarisation of the nitrate anion and thus weakening the N-O bond.
Flame test colours group 2
Magnesium: no flame colour (the energy emitted is outside visible spectrum)
Calcium: brick red
Strontium: red
Barium: pale green
How do you carry out a flame test?
- Use a nichrome wire
- Sterilise the wire by dipping in concentrated hydrochloric acid and then heating in Bunsen flame
- Make sure the sample powdered or grinded
- Dip wire in solid and put in Bunsen flame and observe flame
How are the colours from the flame test formed?
The heat causes the electron to get excited and thus move to a higher energy level but at this higher level the electron is unstable so then moves back down.
As it moves from a higher to lower energy level energy is emitted in the form of visible light energy which is the colour you see.
What group elements are referred to as halogens?
Group 7
List 2 properties of halogens
● Low melting and boiling points
● Exist as diatomic molecules
What is the trend in boiling point down group 7? Why?
Increases down the group because: -size of atom increases as more occupied electron shells → stronger London forces of attraction between molecules, take more energy to break
What is the trend in reactivity down group 7? Why?
Reactivity decreases because:
● Atomic radius increases
● Electron shielding increases
● Ability to gain an electron and form 1- ions decreases
Explain the trend of electronegativity down group 7
Down the group the electronegativity of the elements decreases.
This is because the atomic radii increases due to the increasing number of shells so there is reduced nuclear attraction between the outermost electron and the nucleus.
What is the trend in oxidising ability down the group? Why?
Decreases down group (Cl strongest, I weakest)
This is because Cl has the fewest occupied electron shells, greatest force of attraction between outer electrons and nucleus and thus is the easiest to gain electrons and be reduced → best oxidising agent
What is the trend in reducing ability of the halides down the group? Why?
Increases down the group (Cl- weakest, I- strongest)
This is because I- has the most occupied electron shell so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of nucleus and thus is the easiest to be oxidised and lose electrons → best reducing agent
When a more reactive halogen displaces a less reactive halide, what is the reaction called?
Displacement reaction
What is the colour of chlorine in water?
Pale green
What is the colour of bromine in water?
Orange
What is the colour of iodine in water?
Brown
What is the colour of chlorine in cyclohexane?
Pale green
What is the colour of bromine in cyclohexane?
Orange
What is the colour of iodine in cyclohexane?
Violet
Out of the 3 halides Cl-, Br- & I-, which one of these can be oxidised by chlorine?
Br- & I- ions
Write the equation for chlorine oxidising bromide ions
Cl₂ (aq) + 2Br- (aq) → 2Cl- (aq) + Br₂ (aq)
Yellow solution
Write the equation for Cl2 oxidising 2I- in cyclohexane and associated colour change
Cl₂ (aq) + 2I- (aq) → 2Cl- (aq) + I₂ (aq)
Purple solution
Out of the 3 halides Cl- , Br- & I- , which one of these can be oxidised by bromine?
I- ions
Write the equation for bromine oxidising iodide ions
Br₂ (aq) + 2I- (aq) → 2Br- (aq) + I₂ (aq)
Brown solution
Out of the 3 halides Cl- , Br- & I- , which one of these can be oxidised by iodine?
Does not oxidise Cl- or Br-
Define disproportionation
The oxidation and reduction of the same element in a redox reaction
What is the equation for the reaction of Cl2 with water?
Cl₂ (g) + H₂O (l) → HClO (aq) + HCl (aq)
What type of reaction is the reaction of chlorine with water?
Disproportionation; chlorine is both oxidised and reduced
Why is chlorine added to drinking water?
It kills the bacteria in the water and makes it safer to drink
What are the two forms of the chlorate ion?
ClO- is chlorate (I)
ClO₃- is chlorate (V)
What is the equation for forming bleach?
Cold dilute alkali
Cl₂ (aq) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H₂O (l)
NaClO is bleach
Show that the reaction of chlorine with hot dilute NaOH is a disproportionation reaction
3Cl2 (aq) + 6 NaOH(aq) 5 NaCl (aq) + NaClO3 (aq) + 3H2O (l)
Chlorine is been reduced and oxidised.
Oxidation state of chlorine has gone from:
0 to -1 in NaCl = reduction
0 to +1 in NaClO3 = oxidation
What do you use to test for halide ions?
Acidified Silver nitrate
AgNO3
Why do you add HNO3? Why not HCl?
To remove CO₃2
Adding HCl would add Cl- ions, giving a false positive result
Result and equation for Chloride (cl-) test?
white ppt
Ag+ + Cl- → AgCl (s)
What is the result and equation for the test for Bromide ions (Br-)?
Cream ppt
Ag+ + Br- → AgBr (s)
What is the result and equation for the test for Iodide ions (I-)?
Yellow ppt
Ag+ + I- → AgI (s)
What happens (+ equations) to each of the silver halide precipitates when dilute/conc ammonia are added?
Silver chloride
Silver chloride (AgCl-) dissolves in both dilute and conc ammonia AgCl (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Cl
What happens (+ equations) to each of the silver halide precipitates when dilute/conc ammonia are added?
Silver bromide
Silver bromide (AgBr)- only dissolves in conc ammonia
AgBr (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Br
What happens (+ equations) to each of the silver halide precipitates when dilute/conc ammonia are added?
Silver iodide
Silver iodide (AgI-) will not dissolve in either concentrated or dilute ammonia
What products are formed when I- reduces H2SO4?
Do equations for all 4. H₂SO₄ + 2I- → SO₄2- + 2HI H₂SO₄ + 2H+ + 2I- → SO₂ + I₂ + 2H₂O (SO2 is a choking gas with a pungent odour) H₂SO₄ + 6H+ + 6I- → S + 3I₂ + 4H₂O (S is a yellow solid) H₂SO₄ + 8H+ + 8I- → H₂S + 4I₂ + 4H₂O (H2S smells of bad/rotten eggs)
What are halogens?
Halogens are oxidising agents
CL2 + 2e- → 2cl
What are halides?
Halides are reducing agents
2Cl → Cl2 + 2e-
The smaller the halogen
the stronger the oxidising power
The larger the halide
the stronger the reducing power
Reduction of sulphur
Whenever sulphur is reduced, it can produce sulphur dioxide, which is further reduced to hydrogen sulphide and then reduced to sulphur
What products are formed when iodide ions reduces Sulfuric acid?
H₂SO₄ + 2I- → SO₄2- + 2HI
What products are formed when iodide ions reduces Sulfuric acid to sulfur dioxide?
H₂SO₄ + 2H+ + 2I- → SO₂ + I₂ + 2H₂O (SO2 is a choking gas with a pungent odour)
What products are formed when iodide ions reduces Sulfur dioxide to sulfur?
H₂SO₄ + 6H+ + 6I- → S + 3I₂ + 4H₂O (S is a yellow solid)
What products are formed when iodide ions reduces Sulfuric acid to hydrogen sulphide?
H₂SO₄ + 8H+ + 8I- → H₂S + 4I₂ + 4H₂O (H2S smells of bad/rotten eggs)
What are the products of Br- + H2SO4?
HBr and SO₂
Does Cl- reduce H2SO4?
No, not a powerful enough reducing agent; only HCl is formed
How can you test for carbonate ions, CO32-?
Add strong acid to the sample
Collect the gas produced
Pass through lime water
What are the observations for a positive test of carbonate ions, CO32-?
Fizzing Limewater turns cloudy
Write an equation for the carbonate ion test
CO32- (aq) + 2H+ (aq) → H2O (aq) + CO2 (g)
How can you test for sulphate ions, SO42-?
● Add dilute hydrochloric acid and barium sulphate to the sample
What are the observations for a positive test of sulfate ions, SO42-?
White precipitate of barium sulfate is produced
Write an equation for the sulfate ion test
Ba2+ (aq) + SO42- (aq) → BaSO4 (s)
When testing for carbonate, sulfate and halide ions, in which order should the tests be carried out and why?
- Carbonate test
- Sulfate test
- Halide test
Because barium ions forms insoluble precipitate of BaCO3 and silver ions form insoluble precipitate of Ag2SO4
How can you test for ammonium ions, NH4+?
Add sodium hydroxide to the sample and warm it
Test the gas produced with red litmus paper
What are the observations for positive ammonium ions test?
● Red litmus paper turns blue ● Ammonia has a pungent smell
Write the equation for ammonium ions test
NH4+ (aq) + OH- (aq) → NH3 (aq) + H2O (aq)
Reactions of group 2 elements with oxygen
Group 2 elements react with oxygen to produce metal oxides
Group 2 oxides produce white solids
Reactions become more vigorous as you go down the group
General equations for the reactions of group 2 elements with oxygen
2X(s) + O2(g) → 2XO(s)
The products are oxides containing X^2+ and O^2- ions
Reactions of group 2 elements with chlorine
The group 2 elements react with chlorine when heated in the gas
Group 2 elements react with chlorine to produce metal chlorides
Reactions become more vigorous as you go down the group
General equations for the reactions of group 2 elements with chlorine
X (s) + Cl2(g) → XCl2 (s)
The products are chlorides containing X^2+ and Cl- ions
Reactions of group 2 elements with water
Group 2 elements react with water to produce metal hydroxides
The reaction between magnesium and water is very slow and does not proceed completely.
Calcium, strontium and barium react with increasing vigour (i.e. down the group), which can be seen by the increase in effervescence
Observations when group 2 elements react with water
One would observe:
- Fizzing, (more vigorous down group)
- The metal dissolving, (faster down group)
- The solution heating up (more down group)
- With calcium a white precipitate appearing (less precipitate forms down group)
General equations for the reactions of group 2 elements with water
X (s) + 2H2O (l) → X(OH)2 (aq) +H2 (g)
The products are hydrogen gas and hydroxides containing X2+ and OH- ions
How is the reaction of calcium with water different?
Ca (s) + 2H20 (l) → Ca(OH)2 (S) + H2 (g)
Calcium hydroxide is only slightly soluble in water, so the liquid in this experiment goes cloudy as a precipitate of calcium hydroxide forms
Reaction of magnesium and steam
Magnesium reacts differently when heated in steam - it rapidly produces magnesium OXIDE and hydrogen gas in vigorous reaction.
The Mg would burn with a bright white flame.
Mg (s) + H2O (g) → MgO(s) + H2(g)
Reactions of group 2 oxides with water
The group 2 oxides are classed as basic oxides, which means that they can react with water to form alkalis.
These reactions occur when the oxides are added to water
The solids react to form colourless solutions
They become more strongly alkaline as you go down the group as the hydroxides become more soluble
General equation for the reactions of group 2 oxides with water
XO (s) + H20 → X(OH)2 (aq)
Reactions of the group 2 oxides and hydroxides with acids
All of the group 2 oxides and hydroxides react with acids to form salts and water
These reactions can be described as neutralisation reactions
During the reactions, a white solid reacts to form a colourless solution
The reactions are exothermic
Solubility of group 2 sulfates
The solubility of group 2 sulfates decreases down the group
Magnesium sulfate is classed as soluble
Calcium sulfate is slightly soluble
Strontium sulfate and barium sulfate are insoluble
Solubility of group 2 Hydroxides
The solubility of group 2 hydroxides increases down the group
The effect of heat on the Group 2 carbonates
All the carbonates in this Group undergo thermal decomposition to give the metal oxide and carbon dioxide gas.
All of these carbonates are white solids, and the oxides that are produced are also white solids.
As you go down the Group, the carbonates have to be heated more strongly before they will decompose.
The carbonates become more stable to heat as you go down the Group.
Why do group 2 carbonates/nitrates become more stable as you go down the group?
Group 2 carbonates become more thermally stable going down the group.
As the cations get bigger they have less of a polarising effect and distort the carbonate ion less.
The C-O bond is weakened less so it less easily breaks down
The effect of heat on the Group 2 nitrates
All the nitrates in this Group undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen.
The nitrates are white solids, and the oxides produced are also white solids. Brown nitrogen dioxide gas is given off together with oxygen.
Magnesium and calcium nitrates normally have water of crystallisation, and the solid may dissolve in its own water of crystallisation to make a colourless solution before it starts to decompose.
As you go down the Group, the nitrates also have to be heated more strongly before they will decompose.
The nitrates also become more stable to heat as you go down the Group.
Effect of heat on group 1 nitrates
Group 1 nitrates, with the exception of lithium nitrate, do not decompose in the same way as group 2 nitrates.
They decompose to give a nitrate (III) salt and oxygen.
How do we test the stability of nitrates?
Measure how long it takes for a specific amount of oxygen to be produced using a gas syringe
Or, length of time it takes until a specific amount of NO2 is produced. NO2 is a brown gas that can easily be observed, but is toxic so must be done in a fume cupboard
How do we test the stability of carbonates?
One is to heat a known mass of carbonate in a side arm boiling tube and pass the gas produced through lime water.
Time for the first permanent cloudiness to appear in the limewater.
Repeat for different carbonates using the same moles of carbonate/same volume of limewater/same Bunsen flame and height of tube above flame.
Trends in boiling points of group 7 elements
This increases as we go down the group
This is because the strength of the London forces increase due to the increasing size and relative mass of the atoms, so more energy is needed to break the bonds
The physical state goes from gas at the top of group 7 to solid at the bottom
Fluorine F2
Pale yellow gas
Chlorine Cl2
pale green gas
Bromine Br2
Brown orange liquid
Iodine I2
Grey solid
Trends in electronegativity of group 7 elements
This decreases as we go down the group
As the halogen atoms get bigger, any bonding pair gets further and further away from the halogen nucleus, and so is less strongly attracted towards it.
In other words, as you go down the Group, the elements become less electronegative.
Trends in melting points of group 7 elements
This increases as we go down the group
This is because the strength of the London forces increase due to the increasing size and relative mass of the atoms, so more energy is needed to break the bonds
Trends in reactivity of group 7 elements
As you go down group 7, the halogens become less reactive.
This is because:
- Atomic radius increases
- Nuclear charge increases, so the nuclear attraction on the outer electrons are stronger.
- Electron Shielding increases and outweighs the nuclear attraction.
