8.1(3.1.2) - Reactivity Trends Flashcards
Name of Group 2 elements
Alkaline earth metals
What form are group 2 elements usually found in?
Oxides, as are very reactive
E.g. CaCO3
Most common type of reaction in Group 2 metals
Redox reactions
They are seen as reducing agents
They reduce another species in the reaction
Redox reaction of group 2 with oxygen
All react with oxygen to form a metal oxide
E.g. Magnesium reacts with oxygen in the air
Burns with a very bright white light
Forms magnesium oxide
Oxidation number changes in redox of magnesium with oxygen
Each Mg increases by +2 - (2Mg so +4)
Each O decreases by -2 - (O2 so -4)
Redox reactions of group 2 with water
React with water to form an alkaline hydroxide and hydrogen gas.
Water and Mg reacts slowly
Reaction becomes more vigorous with metals further down the group
Therefore reactivity increases down the group
Oxidation no.s in redox with water(group 2)
E.g Sr + 2H2O —> Sr(OH)2 + H2
Sr increases by 2(+2)
Two H decrease by 1 forming H2
Two H don’t change - forming Sr(OH)2
Group 2 redox reaction with dilute acids
Metal + acid —> salt + hydrogen
Mg - +2 so is oxidised
2H in HCl - each H decreases by 1 (-2 in total)
Group 2 trend in reactivity and ionisation energy
Reactivity increases down the group
Ionisation energy decreases down the group
Explanation for Group 2 trends in reactivity and ionisation energy
Ionisation energies decrease because:
Atomic radius and shielding increases
So attraction to nucleus decreases
Reactivity increases because ionisation energy decreases when forming 2+ ions/losing electrons more readily to react.
Reaction and equation for formation of bleach
What are the conditions needed?
Cl2(aq) + 2NaOH(aq) —> NaClO(aq) +NaCl(aq) + H2O(l)
Conditions required:
- Dilute aqueous sodium hydroxide
- cold conditions
What is a disproportionation reaction?
Where an element in a reaction is both oxidised and reduced
Trend in reactivity of the halogens and explanation
-Reactivity decreases down the group
Explanation:
-Atomic radius increases
-More inner shells so shielding increases
-Less nuclear attraction to capture an electron
-Reactivity decreases
What colour are some of the halogens?
Bromine - Orange/Yellow
Chlorine - pale yellow
Iodine - Brown in solution and purple when a gas
Which halogens displace others and why?
H
Trend in melting point of the halogens
-Boiling and melting point increase down the group
Explanation:
- Elements have more electrons down the group
- So they have more/stronger London Forces
- More energy is required to break more/stronger intermolecular forces
- So boiling point increases
What is a redox reaction?
A redox reaction is a reaction in which one element is reduced and another element is oxidised
What is oxidation?
Loss of electrons
What is reduction?
Gain of electrons
How to test for displacement reactions in halogens - full mechanism
-Add solution of each halogen to aqueous solutions of the other halides
-e.g. add Cl2 to solutions of NaI and NaBr
-If the halogen added is more reactive than the halide present then:
-A reaction takes place, the halogens displaces the glide from solution
-The solution changes colour
-Colours in solutions for halogens are as follows:
-Iodine is brown
-Bromine is orange
-Chlorine is pale green
-Add a solution of cyclohexane to each test tube and shake the mixture fully tell them apart
The colours of the halogens in solution of cyclohexane are as follows:
-Chlorine - pale green
-Bromine - orange
-Iodine - violet
-Then displacements can be shown by presenting reactions as ionic equations - more reactive halogen displaces present halide ion
Benefits and risks of chlorine use
Pros:
- Used in water treatment
- Helps kill bacteria in drinking water(makes it drinkable and safe) and in swimming pools
Cons:
-Chlorine is toxic to humans(in larger quantities) - is an irritant
What are the four quantitative tests?
- Test for carbonates
- Test for sulfates
- test for halides
- Test for ammonium ions
Describe the carbonate test
Outline the equation for the reaction that occurs during testing for CO2
- Add dilute nitric acid to the solid or solution to be tested in the test tube
- If bubbles are produced, the unknown compound could be a carbonate
- To prove the gas is CO2:
- Bubble the gas through lime waterCa(OH)2
- CO2 reacts to form a fine white precipitate of calcium carbonate
- This turns the lime water milky
-CO2(g) + Ca(OH)2(aq) —> CaCO3(s) + H20(l)
Describe the sulfate test
- Add barium chloride
- A white precipitate of barium sulfate forms(BaSO4 is insoluble)
- Ionic equation shown:
- Ba2+(aq) + SO4^2-(aq) —BaSO4
