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Chapter 8 - Reactivity trends I - Coggle Diagram
Chapter 8 - Reactivity trends I
Redox reactions of group 2 elements
Reducing agents
Each group 2 metals has two electrons in the outer s sub-shell
Redox reactions are the most common type of reaction of group 2 elements
Each metal loses two electrons to form a 2+ ion
Another species gains these two electrons and is reduced
Group 2 element is the reducing agent as it has reduced another species
Reactions with oxygen
Group 2 elements react with oxygen to form a metal oxide
Group 2 element is oxidised
Oxygen is reduced
Reaction with water
Group 2 elements react with water to form an alkaline hydroxide and hydrogen
The reaction is more vigorous further down the group
Not all the hydrogen atoms are reduced, in 2H20, 2 atoms decrease by 1 to form H2, and 2 atoms don't change
Reactions with diliute acids
Metal + acid -> salt + hydrogen
Metal is oxidised
H+ in the acid is reduced
Reactivity trend and ionisation energy
Atoms of group 2 elements react by losing electrons to form +2 ions
Formation of 2+ ions from gaseous atoms require the input of two ionisation energies
Ionisation energies decrease down the gropup as the attraction between the nucleus and outer electrons decrease as atomic radius and shielding increase
Total input energy from ionisation energies to form 2+ ions decreases down the group
Group 2 elemebts become more reactive and stronger reducing agents down the group
Reactions of group 2 compounds
Group 2 oxides
Reactions with water
Oxides of group 2 elements react with water to release hydroxide ions and form alkaline solutions of the metal hydroxides
Group 2 hydroxides are only slightly soluble in water, when solution becomes saturated, any further metal/hydroxide ions will form a solid precipiate
Solubility of hydroxides
Increases as you go down the group
Resulitng solutions contain more OH- ions and are more alkaline
Experiment
Add one spatula of each Group 2 oxide to water in a test tube
Shake the mixture, the solution is saturated and a white solide will form at the bottom of the test-tube
Measure the pH of each solution, the alkalinity will be seen to increase
Ionic radius increases, charge density decreases, metal ions are less attracted to OH-, so species dissociate more easily
Solubility of Sulfates
Decrease as you go down the group
Sulfate ion is larger, larger cations form stronger ionic compounds
Group 2 compounds as bases
Agriculture
Calcium hydroxide is added to fiels as lline by farmers to increase the pH of acidic soils
Calcium hydroxide neutralises acid in the soil to form neutral water
Medicine
Used as antacids for treating acid indigestion
Magnesium and calcium carbonates are used
Milk of magnesia is a suspension of white magnesium hydroxide in water
Stomach acid is mainly HCL
