Group 2

Question 1

Group 2 elements with oxygen:

Answer 1

2M (s) + O2 → 2MO (s)
Ex. 2Mg (s) + O2 (g) → 2MgO (s)

Sr and Ba form MO2
2Ba (s) + O2 (g) → 2BaO (s)
Ba (s) + O2 (g) → BaO2 (s)

(oxides formed are white solids)

Question 2

Group 2 elements with water:

Answer 2

M (s) + H20 (I) → M (OH)2 (aq) + H2 (g)

Exception:

Be doesn’t react with water
When magnesium reacts with steam forms MgO (s)

Question 3

Why the reactivity increases down the group

Answer 3

The atoms get larger and electrons are further away from the nucleus due to increase in shell number and atomic radius increases, shielding increases, therefore it is easier to remove and hence more reactive

Question 4

With dilute HCI

Answer 4

M (s) + 2HCI (aq) = MCI2 (aq) + H2 (g)

Question 5

With dilute H2SO4

Answer 5

M (s) + H2SO4 (aq) = MSO4 (aq) + H2 (g)

Exception:
Mg (s) + H2SO4 (aq) = MgSO4 (s) + H2 (g)

Question 6

Notes about rxn with dilute H2SO4

Answer 6

• CaSO4, SrSO4 and BaSO4 are insoluble
• Solubility of sulfates decrease down the group
• Use a powder + stir

Question 7

Group 2 oxides with water

Answer 7

oxide + water = hydroxide

• basic oxide
• BeO is amphoteric
• Forms alkaline solutions= pH 10
• Solubility of hydroxides increase down the group therefore more -OH ions are available and pH increases, because it becomes more alkaline

Question 8

With HCI

Answer 8

MO + 2HCI = MCI2 + H2O

Question 9

Thermal Decomposition

Answer 9

The breakdown of a compound into 2 or more different substances using heat

Question 10

Carbonates

Answer 10

• Group 2 carbonates break down (decompose) when heated and form metal oxide + carbon dioxide gas
• going down the group, more heat is needed to break down the carbonates

Question 11

General equation for decomposition of group 2 carbonates

Answer 11

MCO3 (s) = (heat) MO (s) + CO2 (g)

Question 12

Nitrates decompose to form

Answer 12

metal oxide + nitrogen dioxide gas (observed as brown fumes and is toxic) and oxygen gas

Question 13

General equation for decomposition of group 2 nitrates

Answer 13

2M(NO3)2 (s) = (heat) 2MO (s) + 4NO2 (g) + O2 (g)

Question 14

Thermal stabilities trend

Answer 14

• Going down group 2 more heat is needed to break down the carbonate and nitrate ions and therefore thermal stability increases

Question 15

Thermal stability trend explained

Answer 15

• more heat is needed to break down the carbonate and nitrate ions, therefore thermal stability increases down the group
• as you go down the group the atoms gain more shells, therefore it cant pull e- easily therefore heat is required

Question 16

Group 2 chemical trends

Answer 16

• they have 2 electrons in their outermost principal quantum shell
• all the elements can form ionic compounds in which they donate these 2 outermost electrons (act as reducing agents) to become an ion with a +2 charge (so they themselves become oxidised)
• going down the group they become more reactive

Question 17

First ionisation energy

Answer 17

energy needed to remove the first outer electron of an atom

Question 18

Second ionisation energy

Answer 18

energy needed to remove the second outer electron of an atom

Question 19

Going down the group it becomes easier to remove the outer 2 electrons of the metals, because:

Answer 19

• though the nuclear charge increases down the group (more protons), increased shielding effect and larger distance between the outermost electrons and the nucleus outweighs the attraction of the higher nuclear charge
• because of this the elements become more reactive going down the group as it gets easier for the atoms to lose 2 electrons and become 2+ ions

Question 20

Reactions show this:

Answer 20

With dilute HCI: bubbles of H gas given off much faster, indicating that reactions become more vigorous

With oxygen: the metals get more reactive with oxygen down the group (Ba is so reactive that it must be stored in oil to prevent it mixing with oxygen in the air)

Question 21

Physical trends: going down the group the melting point decreases because:

Answer 21

• going down the group the elements become larger as the outer electrons occupy a new principal quantum shell which is further away from the nucleus
• m.p. of the elements therefore decrease down the group as the outer electrons get further away from the nucleus and the attraction between the nucleus and bonding electrons decrease, causing a decrease in m.p.
• density increases down the group

Question 22

Trend in solubility of hydroxides: solubility increases down the group, because:

Answer 22

• solutions formed from the reactions of the group 2 metal oxides and water become more alkaline going down the group as the concentration of -OH ions increases, which increases the pH of the solution
• therefore, going down the group the alkalinity of the solution formed increases when group 2 oxides react with water

Question 23

Hydroxide dissolving in water

Answer 23

M(OH)2 (aq)= M (aq) + 2OH- (aq)

Question 24

Trend in solubility of sulfates:

Answer 24

solubility decreases down the group