Chapter 8 - Reactivity Trends Flashcards
What are the typical physical properties of group 2 elements?
Metals
Do not occur in elemental form naturally
Very reactive
What is a reducing agent?
Reduces another species so therefore becomes oxidised itself
Loses electrons
e.g. Group 2 elements
What is formed when a group 2 metal reacts with oxygen?
Metal oxide
MO (M = metal)
What is formed when a group 2 metal reacts with water?
Alkaline hydroxide and hydrogen
M(OH)2
What is formed when a group 2 metal reacts with a dilute acid?
Salt and Hydrogen
How does reactivity change down group 2?
Reactivity increases
Why does reactivity change down group 2?
1st and 2nd ionisation energies decrease down the group
Therefore both of the electrons become easier to lose
Attraction between the electrons and the nuclei decreases
Atomic radius increases
Electron shielding increase
All of this makes the electrons easier to lose to other substances and increases the reactivity
How does solubility change down group 2 hydroxides?
Increases
How does pH change down group 2 hydroxides?
Increases and therefore it becomes more alkaline
How can solubility and pH changes be demonstrated between different group 2 hydroxides?
Add spatula of group 2 oxide to test tube of water
Shake mixture
Not all of the metal hydroxide can dissolve in the water leaving some which solid at the bottom
Measure pH and it should decrease as more alkaline solution down the group
Why are group 2 compounds good bases?
Often forms hydroxides, oxides and carbonates
All of which can neutralise acids
How is calcium hydroxide used in agriculture?
Neutralises acid in the soils
Forms neutral water
How are group 2 compounds used in medicine?
Antacids for indigestion
Magnesium and calcium carbonate neutralises HCl (stomach acid)
What are the physical properties of halogens?
Naturally occur as diatomic molecules
Highly reactive
How does boiling point change down group 17?
Increases
Why does boiling point change down group 17?
There are more electrons overall
More London forces
More energy to overcome the IMFs
Therefore boiling point increases
What is the state and colour of Fluorine at RTP?
Pale yellow gas
What is the state and colour of Chlorine at RTP?
Pale green gas
What is the state and colour of Bromine at RTP?
Red-brown liquid
What is the state and colour of Iodine at RTP?
Shiny grey-black solid
What is an oxidising agent?
Oxidises another species and therefore gets reduced
It gains electrons
e.g. Group 17 (Halogens)
What is a displacement reaction and why do they happen?
When a halogen replaces a halide in solution
Happens due to differences in reactivity down the group
A more reactive halogen will displace a less reactive halide in solution
Can be observed through a colour change
How does reactivity change down group 17?
Decreases
Why does reactivity change down group 17?
Atomic radius increases
More inner shells so more electron shielding
Less attraction between the nuclei and an electron from a reacting species
Therefore reactivity decreases down the group
What is disproportionation?
Redox reaction where the same element is both oxidised and reduced in the same reaction
e.g. Chlorine with water or cold, dilute sodium hydroxide
How is chlorine used in water purification?
Kills any harmful bacteria in the water
Reduces the risk of water borne diseases significantly making it safe to drink
Can react with organic hydrocarbons to form chlorinated hydrocarbons which could be a cause of cancer
However if the water was not purified the risk of the drinking the water would be significantly higher
What is the qualitative analysis test for carbonates?
Add an acid (most likely dilute nitric acid)
If bubbles can be seen collect some of the gas and bubble through lime water to confirm if it is carbon dioxide
If the limewater goes cloudy then the substance was a carbonate
What is the qualitative analysis test for sulfates?
Add barium chloride or barium nitrate
If a white precipitate forms (barium sulfate) then a sulfate ion is present
What is the qualitative analysis test for halide ions?
Add aqueous silver nitrate
If a precipitate is formed a halide ion is present
Chloride = White
Bromide = Cream
Iodide = Yellow
To confirm which precipitate it is aqueous ammonia can be added to confirm which halide ion is present
Chloride = Soluble in dilute NH3
Bromide = Soluble in concentrated NH3
Iodide = Insoluble in concentrated NH3
What is the qualitative analysis test for ammonium ions?
Add aqueous sodium hydroxide
Warm the mixture gently
Test the pH with indicator paper
If the paper turns blue when ammonium ions are present
What is the correct order to test for each ion in the same test tube?
Carbonate (use nitric acid)
Sulfate (use barium nitrate)
Halides
