Chapter 10: Group 2 Flashcards
What do metals form when they react with oxygen?
Metal Oxides
Describe and explain the reaction of beryllium with oxygen.
Beryllium is reluctant to burn with oxygen unless it is in a dust form
This is because it has a strong thin layer of oxide that stop it from making contact with the oxygen
How does beryllium look when burning in a flame?
With silvery sparkles
Magnesium’s flame?
Intense white
How does calcium burn?
Initially it is reluctant
Then suddenly starts burning with an intense white flame with red tinges at the end
How does strontium burn?
Initially does not burn
Then suddenly starts burning
With red tinges around the outside
How does barium burn?
With a pale green flame
What are the 2 group 2 elements that burn to form peroxides?
Barium and Strontium
Describe the burning and the conditions required to for strontium peroxide.
Strontium will have to be heated with oxygen under very high pressures
How does barium peroxide form?
The barium will produce barium peroxide and barium dioxide when just normally heated with oxygen
Describe the reaction of a group 2 metal with air.
They will form the respective metal oxide and the metal nitride
Why does the activation energy of a reaction fall?
Because the ionisation energies are falling
Describe the polarisation of a negative peroxide ion.
As the ion with a positive charge gets closer the electrons are attracted to it and then it increases the chance of a simple oxide forming.
Why is barium able to form a peroxide ion but not other group 2 metals?
Its higher shielding means that the positive charge is not strong enough to break up the nitride molecule
Why can group 2 form nitrides but not group 1
The higher charge compensates for the energy loss by releasing more energy due to a higher lattice energy.
Describe the reactivity of magnesium in cold water
It will react tot form a weakly alkaline solution.
When do we get magnesium oxide and hydrogen when reaction magnesium with water?
When the magnesium is hot and the the water is in the form of steam.
Describe the reaction of calcium with water
It reacts more readily
It forms calcium hydroxide solution that is weakly alkaline
Hydrogen gas is given off
What is the trend with the reaction of water of group 2 metals?
The hydrogen gas is given off more rapidly.
What happens when water is added to calcium hydroxide?
There is a very exothermic reaction
Calcium hydroxide is produced
The calcium hydroxide swells up and lots of steam is produced
How do we form lime water?
Very small amounts of calcium oxide is added to water that forms a strongly alkaline solution.
Describe the trend of solubilities going down group 2.
The solubilities of the hydroxide increases going down the group, and therefore the resulting solution will have higher pH’s.
Describe the trend of group 2 sulphates going down the group.
The sulphates become less and less soluble.
Describe the reaction of a group 2 oxide with a dilute acid.
Since they are all basic oxides, they will just give salt and water
Describe the reactions of a group 2 metals with a dilute sulphuric acid.
They make their respective sulphate salts.
However, calcium sulphate os only sparingly soluble while barium sulphate is not at all soluble.
What is the trend in the solubility of sulphates?
The sulphates become less soluble as you go down the group
Describe the trend is the solubilities of carbonates as you go down the group.
The tend to become less soluble going down.
How do carbonates react with dilute acids?
They give the salt, carbon dioxide and water.
Describe the trend in the thermal decomposition of carbonates going down the group?
The carbonates tend to become more and more thermally stable going down the group
What do the carbonates produce going down the group?
They produce the metal oxide and carbon dioxide.
What is the gas that forms when group 2 nitrates are heated
It forms the NO2 gas that is brown and toxic.
What is the trend in atomic radius of group 2?
The atomic radius increases as you go down the group
What is the trend of the first Ionisation energy of the elements in group 2.
It falls going down the group
What is the trend of electronegativity going down the group?
it falls.
The atoms become less and less good at attracting the pair of electrons.
Why can beryllium not form ions?
The size of the atom is too small, and so the electron pair is held very strongly
Even in the state of a bond, the pair is brough much closer to the beryllium nucleus.
Describe the trend of melting points of group 2.
It decreases down the group except for magnesium which has a veyr low melting point.
What is the general trend when a metal reacts with cold water and when it reacts with steam. What is the reason for this?
Cold water - Metal Hydroxide
Steam - Metal Oxide
Reason - At the high steam, the metal hydroxides thermally decompose to give the oxide and water.
How do calcium, strontium and Barium react with cold water?
They react with increasing vigour to give the hydroxide and hydrogen.
The reaction is very exothermic.
What is the trend of the hydroxides that form when group 2 reacts with steam?
The hydroxides get increasingly soluble, with calcium being a precipitate.
What is the role of lime in agriculture?
To raise the soli pH
