Groups 1 & 2 Flashcards
Trend in ionisation energy down group 2
First ioniation energy decreases going down group 2, due to:
* Greater atomic radius
* Increased shielding
Making it easier for an electron to be removed, and requiring less energy
Trend in reactivity of group 2 elements down the group and reasons
Reacitivity increases going down group 2, due to:
* Greater atomic radius
* Increased shielding
Making the outer electrons easier to lose
Reactions of Mg, Ca, Sr and Ba (g2 elements) with water
Reactions with water
Group 2 metals react with water in a redox reaction. The metal hydroxide forms as an alkaline solution
Mg + 2H2O –> Mg(OH)2 + H2
Mg reacts much quicker if steam is used
Mg + H2O –> MgO + H2
Reactions of Mg, Ca, Sr and Ba (g2 elements) with oxygen
Reactions with oxygen
Group 2 metals react with oxygen to form oxides. once the reaction has been initiated it is vigorous.
General equ for g2 metals + oxygen:
2Mg + O2 –> 2MgO
Strontium and barium can react with excess oxygen and heat energy to form metal peroxides
Sr/Ba may react with oxygen to form a peroxide:
Sr+ O2 –> SrO2
Reactions of Mg, Ca, Sr and Ba (g2 elements) with chlorine
Reactions with chlorine
Group 2 metals react with chlorine gas to produce metal chlorides, (white precipitates)
Mg + Cl2 –> MgCl2
Reactions of group 2 elements with dilute acid
Group 2 metals react with dilute acids to produce bubbles of hydrogen gas and solutions of metal compounds
Hydrochloric acid:
Mg + 2HCl –> MgCl2 + H2
Sulphuric acid:
Mg + H2SO4 –> MgSO4 + H2
Nitric acid:
Mg + 2HNO3 –> H2 + Mg(NO3)2
Reactions of group 2 hydroxides with dilute acid
Group 2 hydroxides react with dilute acid to form a salt and a water. This is a type of neutralisation reaction.
The salt formed depends on the acid used:
* Hydrochloric acid forms chloride salts
* Sulphuric acid forms sulphate salts
* Nitric acid forms nitrate salts
Ex calcium hydroxide and hydrochloric acid:
Ca(OH)2 + 2HCl –> CaCl2 + 2H2O
Trends in solubility of the hydroxides and sulphates of group 2 elements
Group 2 hydroxides increase in solubility going down the group
Group 2 sulphates decrease in solubility going down the group
Barium chloride is used to test for sulphate ions as it reacts to form barium sulphate which is a white precipitate
Trends in thermal stability of the nitrates and the carbonates of the group 1 elements
Group 1 nitrates and carbonates undergo thermal decomposition upon heating under aerobic conditions
Lithium reacts in a similar way to group 2 elements:
* Lithium nitrate produces lithium oxide, nitrogen oxide and oxygen
4LiNO3 –> 2Li2O + 4NO2 + O2
* Lithium carbonate produces lithium oxide and carbon dioxide
The rest of the group 1 metals don’t react in the same way as they rarely go to completion:
* Remaining group 1 nitrates produce a metal nitrite and oxygen
2XNO3 –> 2XNO2 + O2
* Remaining group 1 carbonates do not decompose on heating in a lab as they require extremely high temperatures to do so
Trends in thermal stability of the nitrates and the carbonates of the group 2 elements
Group 2 carbonates and nitrates undergo thermal decomposition to produce solid metal oxide and a variety of gases. This is done by heating the substance in aerobic conditions.
Group 2 carbonates produce carbon dioxide along with the metal oxide (which is a white powder)
XCO3 –> XO + CO2
going down group 2 more heat is required for this reaction as:
* Ions increase in size
* Carbonates increase in thermal stability
Group 2 nitrates produce nitrogen oxide and oxygen along with the metal oxide (which is a white powder)
2X(NO3)2 –> 2XO + 4NO2 + O2
Again, going down group 2 more heat is required for this reaction as:
* Ions increase in size
* Nitrates increase in thermal stability
Explanation of the trends in thermal stability of the elements in group 1 and 2
The elements of group 1 and 2 form more stable carbonates and nitrates going down the group, therefore requiring more energy to undergo thermal decomposition
Reasons for increasing thermal stability
* smaller cation charge
* larger atomic radius
Lower charge and larger atomic radius mean the element is not as polarising, which distorting the electron cloud less and weakening the bonds within the carbonate/sulphate less, meaning it requires more energy to decompose
This means that going down both group 1 and 2 thermal stability increases, and group 1 elements are more thermally stable than group 2 elements
The formation of characteristic flame colours by group 1 and 2 compounds in terms of transitions
- Electrons move up energy levels due to the introduction of energy
- Electrons return to a lower energy level
- The energy realeased from the atom is visible light
- Different energy gaps and therefore energy released in different elements emit different flame colours
Flame colours of group 1 and 2 compounds
(Li, Na, K, Rb, Cs)
(Mg, Ca, Sr, Ba)
Group 1:
* Lithium - red
* Sodium - orange/yellow
* Potassium - Lilac
* Rubidium - violet
* Caesium - violet
Group 2:
* Magnesium - no colour
* Calcium - brick red
* Strontium - crimson red
* Barium - pale green
Experimental procedure to show: Patterns in thermal decomposition of group 1 and 2 nitrates
Experiment
Group 1 and 2 nitrates
1. Put a small spatula of each nitrate in a heating test tube
2. Heat with blue flame, gently and then more strongly
3. Do not melt test tube or heat strongly for more that 2 mins
4. Note appearance of solid before and after heating, time taken to decompose (if it does) and test whether NO2 and/or O2 is produced.
When a nitrate is heated, two gases may be evolved - oxygen and nitrogen dioxide:
* Nitrogen dioxide is brown, identifiable by its colour. It is toxic in high concentrations and should be placed in a fume cupboard if produced
* Oxygen can be tested for if a glowing splint held in the text tube is relit
Experimental procedure to show: Patterns in thermal decomposition of group 1 and 2 carbonates
Experiment
Group 1 and 2 carbonates
1. Put a spatula of the carbonate into a dry heating tube
2. Heat with a blue flame, gently at first and then more strongly
3. Do not melt test tube or heat strongly for more that 2 mins
4. Test any gas given off with limewater and time how long it takes fot it to turn cloudy (if it does)
5. Note appearance of solid before and after heating, time taken to decompose, whether CO2 is involved and the degree of cloudiness of the limewater
6. Repeat with each carbonate, using a fresh sample of lime water of equal volume each time.
Experimental procedure to show: Flame colours in compounds of group 1 and 2 elements
Experiment
1) Take a nichrome wire and clean it by dipping it into a solution of concentrated hydrochloric acid and then into a blue bunsen burner flame
2) Repeat this cleaning until there is no colour produced in the flame
3) Dip the wire into the unknown metal compound and place it into the flame
4) Observe the flame colour produced
What is limewater’s formula?
Calcium hydroxide
Ca(OH)₂
