8.1 - Group 2 Flashcards
What are group 2 elements commonly referred too ?
Alkaline earth metals
What are the ions forms by group 2 atoms ?
2+
How many electrons will group 2 atoms lose to form ions ?
2
In reactions are group 2 atoms reduced or oxidised ?
Oxidised
In reactions what do group 2 elements later act as ?
Reducing agents
How many electrons do they have in their S sub shell ?
2
State the equation for the reaction of group 2 elements with oxygen
Group 2 element + oxygen —> metal oxide
State the equation for the reaction of group 2 elements with water
Group 2 element + water —> alkaline hydroxide + hydrogen
State the equation for the reaction of group 2 Elements with dilute acids
Metal + acid —> salt + hydrogen
State the trend in reactivity down group 2
Reactivity increases down the group
State the trend in ionisation energies down group 2 and state why
- ionisation energy decreases down the group because the attraction between the nucleus and outer electron decreases
- as a result of increasing atomic radius and increasing shielding
State what occurs during the reaction of group 2 metal oxide and water
Hydroxide ions are released, forming alkaline solutions of the metal hydroxide
State what occurs to the metal oxide and water reaction when the solution becomes saturated
Metal and hydroxide ions will form a solid precipitate
How can you see from their reactions that reactivity increases down the group ?
Reactions will be faster and more vigorous
Why does reactivity increase down group 2 ?
- atomic radius increases —> more shells
- increasing shielding —> more inner shells
- less nuclear attraction despite increased nuclear charge
= less energy to remove outer electrons
Show the reaction of magnesium with oxygen and explain what occurs
2Mg (s) + O2 (g) —> 2MgO (s)
0 ———————> +2 = oxidation
0 ————> -2 = reduction
The total changes in oxidation number balance :
- 2 Mg in 2Mg = each Mg increases by +2 = total increase = +4
- 2 O in O2 = each O decreases by -2 = total decrease = -4
What is the general formula for group 2 elements with water
X (OH)2 + hydrogen gas
Explain the reaction with Sr and water and state the balanced equation
Sr (s) + 2H2O (l) —> Sr(OH)2 (aq) + H2 (g)
0 —> +2 = oxidation
+1 ———————> 0 = reduction
Not all the hydrogen atoms are reduced :
- 1 Sr in Sr —> Sr increases by 2 = total increase = +2
- 4 H in 2H2O ——> 2 H decrease by 1 forming H2 = total decrease = -2
2 H do not change forming Sr(OH)2
Explain the reaction of Magnesium and diluted hydrochloric acid and state the equation
Mg (s) + 2HCl (aq) —> MgCl2 (aq) + H2 (g)
0 —> +2 = oxidation
+1 —> 0 = Reduction
The total changes I’m oxidation number balance :
- 1 Mg in Mg = Mg increases by 2 = total increase = +2
2 H in 2HCl = each H decreases by 1 = total decrease = -2
How does the solubility and alkalinity of group 2 hydroxides change down the group ?
Increases
Give an example of group 2 oxide with water
CaO (s) + H2O (l) ———-> Ca^2+ ( aq) + 2OH- (aq)
How does the pH of resulting solutions from group 2 hydroxides change down the group ?
Increases
Explain the solubility of group 2 hydroxides in water ?
- increases down the group
- therefore resulting solutions contain more OH- (aq) ions and are more alkaline
- Mg(OH)2 is only very slightly soluble in water = solution has a low OH- (aq) concentration and a pH = 10
- Ba(OH)2 (s) is much soluble in water = solution has a greater OH- (aq) concentration and a pH = 13
What is the trend in alkalinity in group 2 hydroxides ?
- solubility increases
- pH increases
- alkalinity increases
