Topic 4: Inorganic Chemistry & The Periodic Table Flashcards
Does ionisation energy increase or decrease down group 2
Decrease
Explain the trend in ionisation energy down group 2
Despite the increase in nuclear charge the combined effect of the following factors results in a decrease in ionisation energy down the group:
- As each quantum shell is added energy of the outermost electrons increases
- As the number of filled shells increases their force of repulsion on the electron being removed increases
Explain the trend in reactivity down group 2
General increase in reactivity down the groups explained by the decrease in energy required to remove the 2 electrons from each atom of the element (ionisation energy)
Describe the trend in reactivity of group 2 metals with oxygen
Reactions are more vigorous down the group due to sum of ionisation energies decreasing down the group
For all of the reactions, the element needs to be heated for the reaction to start although even without, there is a slow reaction if the element is exposed to air (surface coating of oxide which prevents further reaction)
Why is each successive ionisation energy greater than the last
- As each electron is removed there is less repulsion between electrons and so they will be drawn slightly closer to the nucleus.
- As the distance of each electron from the nucleus decreases slightly the nuclear attraction increases
- More energy is required to remove each successive electron
How is barium (the most reactive element in group 2) often stored in order to keep it from reacting with the oxygen and water vapour in the air ?
Under oil
Describe the trend in reactivity of group 2 metals with chlorine
Group 2 elements combine with chlorine when heated in the gas.(form ionic bonds)
Reactions become more vigorous down the group (trend harder to see than reaction with oxygen) as sum of ionisation energies decreases down the group
Describe the trend in reactivity of group 2 metals with water
Reaction of magnesium with water is very slow and does not proceed completely
Calcium, strontium and barium react with increasing vigour which can be seen by increasing effervescence due to sum of ionisation energies decreasing down the group
Why does the liquid go slightly cloudy when calcium reacts with water
Precipitate of calcium hydroxide forms as calcium is only slightly soluble in water
Describe how magnesium reacts when heated in steam
Rapidly forms magnesium oxide (white solid) and hydrogen gas
Why is the hydrogen produced during the reaction with magnesium and steam brunt as it leaves the tube ?
Safety reason : prevents the escape of a highly flammable gas into the lab
Give the general equation for the reaction of group 2 metals with oxygen
2M(s) + O2(g) —-> 2MO(s)
Give the general equation for the reaction of group 2 metals with chlorine
M(s) + Cl2(g) —-> MCl2(s)
Give the general equation for the reaction of group 2 metals with water
M(s) + 2H2O(l) —-> M(OH)2(aq) + H2(g)
With calcium:
Ca(s) + 2H2O(l) —-> Ca(OH)2(s) + H2(g)
Describe how group 2 oxides react with water
Group 2 oxides are classed as basic oxides, which means that can react with water to form alkalis
Observation :
Solids react to form a colourless solutions
Describe the trend in solubility of group 2 hydroxides (formed from reaction of group 2 oxides with water)
What effect does this have on the pH of the solutions formed ?
Solubility increases down the group
pH value increases down the group
Describe how you would test for carbon dioxide
Bubbled through limewater. (Ca(OH)2)
Cloudy precipitate indicates positive test
CO2 + Ca(OH)2 ——> CaCO3 + H2O
What is milk of magnesia and explain how it is used
Milk of magnesium is essentially a suspension of magnesium hydroxide in water
It is sold as an indigestion remedy (acts as an antacid)
It neutralises some of the excess HCl in the stomach
Mg(OH)2 + 2HCl —-> MgCl2 + 2H2O
Why is milk of magnesia not a risk
Although hydroxide ions attack human tissue, the very low solubility of magnesium hydroxide means that the conc of OH- ions in the medicine is very low = no risk to health 
Describe the reactions of group 2 oxides and hydroxides with acids
React to form salt + water
Described as neutralisation reactions
White solid reacts to form colourless solution
How is calcium hydroxide (group 2 hydroxide) used in agriculture
Neutralises excess acidity in the soil and increases yield of crops
Describe the trend in solubility of group 2 sulfates
Decreases down the group
How can you test for the presence of sulfate ions in an aq solution
Adding a solution containing barium ions (usually barium chloride or barium nitrate) & dilute hydrochloric/nitric acid
Any sulfate ions in a solution react with the added barium ions to form the white precipitate of barium sulfate
Why should you also add dilute nitric/hydrochloric acid as part of the test for sulfate ions
There are other anions that could also form a white precipitate with barium ions, especially carbonate ions, so in the test there must be H+ ions present to prevent them from forming
What is a barium meal ?
Barium sulfate is used in hospitals (not poisonous as its insoluble)
soft tissues show up more clearly on x-rays due to dense white solid
If something is very thermally stable, what does it mean?
A compound will not decompose at all
Describe the general trends in thermal stability of group 1 compared to group 2 (both nitrates and carbonates)
Group 1 :
Lithium decomposes
Remaining don’t decompose, except at very high temps
Group 2:
Thermally decomposes but with more difficulty down the group
decomposition occurs when the cation has a +2 charge or when the cation has a +1 charge but is also the smallest group 1 cation (only lithium)
Explain the differences between the thermal stabilities of group 1 and 2 nitrates/carbonates
- Smaller and more highly charged cations have greater ability to polarise the complex anion causing it to become less stable
