3.2.2 Group 2 (Alkaline Earth Metals) Flashcards
What ions are formed when group 2 metals react and why?
2+ ions
They all have 2 electrons in their outer shell, so lose 2 electrons when they react
What does the electronic configuration of group 2 atoms always end in?
S2
What is the trend in atomic radius down group 2?
Atomic radius increases as we go down group 2 as the number of energy levels increases.
What is the trend in first ionisation energy down group 2 and why?
1st ionisation energy decreases as we go down group 2.
Extra shells are added as we go down group 2
More shielding so weaker attraction between nucleus and outer electrons
Outer electrons are further from the nucleus so weaker attraction
Makes it easier to remove the outer electron so less energy needed.
(Note that shielding overrides the increase in proton number)
What is the trend in melting points as we go down group 2 and why?
General decrease in melting points as we go down group 2.
They form metallic structures (+ve ions attracted to -ve delocalised electrons)
As we go down the group, the size of the metal ion increases but the number of delocalised electrons remains the same, and the 2+ charge remains the same.
Larger ions means the distance between +ve nuclei in metal ions and delocalised electrons is greater so weaker forces of attraction.
Easier to overcome (break bonds) so less energy required.
MAGNESIUM is an exception due to its structural arrangement compared to other group 2 metals.
What is formed when group 2 metals react with water?
Metal hydroxides (bases)
What is the trend in reactivity with water down group 2 and why?
Reactivity with water increases as you go down group 2
Atomic radius increases down the group
Outer electrons are further from the nucleus
Easier to remove outer electrons so hence more reactive
There is also more shielding.
What is the difference between Mg’s different reactions with water?
Reacts slowly with cold water but vigorously with steam (higher temperature), and produces magnesium oxide instead of a hydroxide.
What is the trend in solubility as we go down group 2 of sulfates and why?
Solubility of sulfates decreases as you go down group 2
If the anion is a double charge (2-) they become less soluble as we go down the group.
What is the trend in solubility as we go down group 2 of hydroxides and why?
Solubility of hydroxides increases as you go down group 2.
If the anion has a single charge (1-) they become more soluble as we go down the group.
What is the test for sulfates?
Barium chloride test
How is the barium chloride test carried out?
Add dilute hydrochloric acid to remove carbonates (could precipitate out after adding barium chloride to give a false result)
Add barium chloride
What is the result for the barium chloride test if sulfates are present?
White precipitate
(Sulfates reacts to form barium sulfate- white precipitate as barium sulfate is insoluble)
What are the 4 uses of group 2 metals?
Neutralisation
Barium meals
Extraction of titanium
Removal of sulfur dioxide from flue gas
Describe how group 2 metals are used for neutralisation?
They are bases when they react with water (metal hydroxides) so can be used to neutralise acids.
Calcium hydroxide is used to neutralise acidic soils in agriculture.
Magnesium hydroxide is used to neutralise excess antacids in the stomach.
What is the ionic equation for neutralisation?
H+ + OH- -> H2O
Describe how barium meals are used in medicine?
Barium sulphate (barium meal) is used in medicine to help identify problems with the digestive tract
Patient drinks a suspension on barium sulfate which lines soft tissues
Patient stands in an X-ray machine which absorbs barium sulfate so soft tissues show up on x-ray.
Why does the toxicity of barium sulfate not matter when using barium meal?
Barium sulfate is insoluble so will not be absorbed into the blood
Describe how magnesium is used in the extraction of titanium?
Magnesium is used to extract titanium from its ore (rutile)
Titanium oxide is converted to titanium chloride by heating it with carbon and chlorine gas.
Titanium chloride is passed through a fractional distillation column to increase the purity
Purified titanium chloride is reduced using magnesium in a 1000* furnace
What is the equation for extraction of titanium for titanium chloride using magnesium?
TiCl4 + 2Mg -> Ti + 2MgCl2
(reduction)
What is titanium used for and why?
Titanium is light and strong so commonly used in planes.
Describe how a group 2 metals can be used to remove sulfur dioxide from flue gas
Use calcium carbonate and calcium oxide to remove sulfur dioxide emissions (that are produced by burning fossil fuels)
Wet scrubbing is used (using an alkali) to neutralise sulfur dioxide in flue gases.
Dissolving calcium carbonate or oxide in water and spraying it on acidic sulfur dioxide gas
This produces calcium sulphite
What is calcium sulfate used for?
The production of plasterboard
What is the equation for flue gas desulfurisation using calcium carbonate?
CaCO3 + 2H2O + SO2 -> CaSO3 + 2H2O + CO2
What is the equation for flue gas desulfurisation using calcium oxide?
Can + 2H2O + SO2 -> CaSO3 + 2H2O
