The Elements Of Groups 1 And 2

Question 1

What are the typical properties of the elements of groups 1 and 2

Answer 1

Relatively high melting / boiling points.
The metals have low densities so they are light.
They form white or colourless compounds so solutions appear clear.

Question 2

How do the mps of group 1 metals compre with group 2 of the same period

Answer 2

Group 1 metals have lower boiling points. Group 2s are higher as the positive ions have a greater charge density and so attract the delocalised electrons more strongly. Also more electrons released per ion.

Question 3

Are group 2 elements oxidising or reducing agents

Answer 3

Group 2 elements are reducing agents (M —> M2+ + 2e-)

Question 4

Explain the trends in ionisation energies in group 2 elements

Answer 4

As you go down group sum of first and second ionisation energy decreases.
Atomic radius increases so electron shielding increases as there are more inner shell electrons.
So the attraction between outer most electrons and nucleus decreases, so less energy to remove outer shell electrons

Question 5

Explain the trend in ability as reducing agents down group 2, by considering ionisation energies

Answer 5

The reactivity of the group 2 metals increases as atomic number increases (as the group is descendent). Down he group, first and second ionisation energies decrease so the formation of cations becomes easier. This means that oxidation becomes easier. i.e. that the group 2 metals become better reducing agents as we go down the group. N.b. The same trend is found for group1 metals, with the same reasoning

Question 6

Describe the reaction of group 2 metals with oxygen

Answer 6

Group 2 metals react vigorously with oxygen to produce metal oxides

Question 7

What is the general equation for the reaction of group 2 metals with oxygen,
And what is the anomaly

Answer 7

2M + O2 —> 2MO (s)

Anomaly: Ba + O2 —> BaO2

Question 8

What is an observation from the reaction of magnesium with oxygen

Answer 8

Mg burns with a white flame

Question 9

What is an observation from the reaction of calcium with oxygen

Answer 9

Ca burns with a brick red flame

Question 10

What is an observation from the reaction of sr with oxygen

Answer 10

Sr burns with a bright red flame

Question 11

What is an observation from the reaction of barium with oxygen

Answer 11

Barium burns with a pale green flame

Question 12

Describe the solid compound formed when group 2 metals react with oxygen

Answer 12

The solid compound which forms is white in colour. This solid will have a lattice / giant structure with strong ionic bonding.

Question 13

Describe the reaction of group 2 metals with water

Answer 13

Magnesium reacts very slowly with water but the reaction becomes much more vigorous as we move further down group 2. The rate of the reaction of magnesium will increase if the metal is reacted with heat

Question 14

What is the general equation for the reaction of group 2 metals with water, and what is the anomaly

Answer 14

M + 2H2O —> M(OH)2 (aq) + H2

Anomaly: Mg + H2O —> MgO (s) + H2

Question 15

Describe the reaction of group 2 metals with acids

Answer 15

Group 2 metals react vigorously with acids to produce a metal salt and hydrogen.

Question 16

What is the general equation for the reaction of group 2 metals with diprotic acid

Answer 16

M + H2A —> MA + H2

Question 17

What is the general equation for the reaction of group 2 metals with monoprotic acid

Answer 17

M + 2HA —> MA2 + H2

Question 18

What observation can be made during the reaction of group 2 metals with acids

Answer 18

During these reactions, the metal dissolves (disappears) as it reacts and a neutral solution of the metal halide salt forms which is approx ph7

Question 19

Write an equation for the reaction of group 2 metal oxides with water

Answer 19

MgO (s) + H2O —> Mg(OH)2 (aq)

Question 20

What is the pH range of the solutions formed in the reaction of metal oxides with water

Answer 20

Alkaline (all contain OH- ions)

Question 21

Describe the oxides formed from group 2 metals

Answer 21

With the exception of beryllium, group 2 metals form basic oxides. These oxides react with acids to form salts. Basic oxides that dissolve in water are alkalis.

Question 22

Write the equation for when calcium oxide reacts with dilute nitric acid

Answer 22

CaO + 2HNO3 —> Ca(NO3)2 (aq) + H2O

Neutralisation reaction

Question 23

Write an equation for the reaction when calcium hydroxide reacts with dilute hydrochloric acid

Answer 23

Ca(OH)2 (aq) + 2HCl —> CaCl2 (aq) + H2O

Neutralisation reaction

Question 24

What’s the equation for the dissociation of metal hydroxides in wager

Answer 24

M(OH)2 (aq) —> 2OH- (aq) + M 2+ (aq)

Question 25

What is the trend in solubility of group 2 metal hydroxides

Answer 25

The solubility of the hydroxide increases the further down the group the metal is

Question 26

What is the trend in alkalinity of the group 2 metal hydroxides dissolved in water as you go down the group

Answer 26

Alkalinity increases as you go down the group as more hydroxide dissociates

Question 27

What is the trend in solubility for group 2 metal sulfatos

Answer 27

The solubility of the sultanes decreases the further down the group the metal is

Question 28

Explain the trends in solubility for group 2 metal hydroxides and sulfures

Answer 28

The more similar the sizes of cation and anion in a compound, the less soluble.
OH- = small ion. So top of group (small cations) not very soluble.
So42- = large job. So bottom of group (large cations) not very soluble

Question 29

What is thermal stability

Answer 29

An indication of the ease with which compounds decompose on heating. Compounds are stable if they do not tend to decompose into their elements or into compounds

Question 30

What’s the equation for the thermal decomposition of MgCO3

Answer 30

MgCO3 (s) —> MgO + CO2

Question 31

What is the trend of the decomposition temperature of the metal carbonates

Answer 31

The decomposition temperature increases with the size of the metal cation i.e. with atomic number. This means that as we go down the group, decomposition becomes more difficult

Question 32

What does decomposition of metal carbonates become more difficult as you go down the group

Answer 32

In group 1 + 2, as you go down the group the charge of ions stays the same but the ionic radius increases. Therefore charge density and polarising power of the ions decreases as you go down the group. This means that the metal ion attracts the bonding electrons in the neighbouring carbonate ion less strongly. So the bonding is less distorted and it is more difficult to break up the negative ion into an oxide ion and carbon dioxide. So decomposition happens less readily, which means that there’s an increase in thermal stability

Question 33

How does the thermal stability of group 1 carbonates compare to that of group 2 carbonates

Answer 33

Group 2 metal carbonates are less stable than group 1 counterparts. Group 2 ions have a higher polarising power has they have a higher charge but a similar radius, so a greater charge density. This attracts the bonding electrons in the carbonate ion more strongly. So the bonds in the carbonate are more distorted, and decomposition happens more readily, which means decreased thermal stability

Question 34

Write the equation for the thermal decomposition of magnesium nitrate

Answer 34

2Mg(NO3)2 —> 2MgO + 4NO2 + O2