9.1 Group 2, alkaline earth metals
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Why are they called the alkaline earth metals
Because their oxides and hydroxides are alkaline
Electron arrangement of group 2
All have 2 electrons on outer shell, outer s orbital. This s orbital gets further away from nucleus going down the group
Atomic radii going down group 2
. It increases because each element has an extra filled energy level of electrons, so outer electrons get further from nucleus each time
Melting points going down group 2
They decrease going down group . Group 2 have high melting points due to their giant metallic structure. . Down the group, the electrons in the sea of delocalised electrons are further away from the positive nuclei. . As a result the strength of metallic bonds decreases going down group
Ionisation energies going down group 2
Group 2 lose 2 electrons in their reactions to form ions with a 2+ charge. So the sum of the first and second ionisation energies are needed for complete ionisation: M is any group 2 metal. M —–> M+ + e- // M+ —> M2+ + e- First and second ionisation energies decrease going down group 2: it takes less energy to remove electrons as they get further from positive nucleus. There’s also more shielding
Pattern of chemical reaction of group 2 with water
. Elements get more reactive going down group.
Redox reaction of group 2 with water equation
M represents any group 2 metal M + 2H20 —> M(OH)2 + H2
What is formed when magnesium reacts with water, and what is its use
Magnesium hydroxide is milk of magnesia. Used in indigestion remedies to neutralise excess stomach acid which causes heartburn, indigestion and wind.
How does magnesium react with water
. Reacts very slowly with cold water, but rapidly with steam to form an alkaline oxide and hydrogen Mg(g) + H20(g)—>. MgO(s) + H2
How does calcium react with water and what is its use and what’s another name for it
Reacts more vigorously with water than magnesium, so reacts with cold water also Called slaked lime and is used to treat acidic soil. Most plants have an optimum level of acidity or alkalinity in which they thrive.
How do strontium and barium react with water Write the equations
They react more vigorously than calcium with water Sr + 2H2O —> Sr(OH)2 + H2 Ba + 2H2O –> Ba(OH)2 +H2
Pattern of the solubility of hydroxides down the group 2
. They become more soluble down group 2 Eg Magnesium hydroxide (milk of magnesia) is almost insoluble so is sold as a suspension in water. . Calcium hydroxide is sparingly soluble and a solution is used as limewater Strontium hydroxide is more soluble Sr(0H)2 . Barium hydroxide is soluble so dissolves to produce a strongly alkaline solution Ba(OH)2 (s) + aq —->. Ba2+(aq) + 2OH- (aq)
Solubility of sulphates going down group use of barium sulphate as a barium meal
They get less soluble down the group, eg barium sulphate is insoluble so can be taken by mouth as a barium meal to outline gut in x rays ( the heavy atom is good at absorbing x rays) Test is safe because its insoluble, but other compounds of it are toxic
Use of barium sulfate to show presence of sulfate ions in tests Write the equation Why is acid added
. Barium sulphate tests for sulfate ions in solution. . Solution is first acidified with HCL then barium chloride is added to solution, and eventually barium sulphate forms which is a white precipitate. Ba2+(aq) + SO42-(aq) –> BaSO4(s) The HCL is added to remove carbonate ions as carbon dioxide. Because barium carbonate is also a white solid which is indistinguishable from barium sulfate