9701 · 27.1
Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds flashcards
Revision flashcards for Cambridge 9701 Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds (syllabus 27.1). Flip, recall, then mark a real past-paper question.
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What are the elements in Group 2 of the periodic table called?
The alkaline earth metals.
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What is the trend in atomic radius down Group 2?
It increases. This is because each element has an additional electron shell compared to the one above it.
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What is the trend in the first ionisation energy down Group 2?
It decreases. The outer electrons are in a higher energy level, are further from the nucleus, and experience more shielding from inner electrons. This outweighs the increase in nuclear charge.
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How does reactivity with water change down Group 2?
Reactivity increases. For example, Mg reacts with steam, Ca reacts with cold water, and Ba reacts vigorously with cold water. This is due to the decreasing ionisation energy.
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What is the trend in solubility for Group 2 hydroxides, $M(OH)_2$?
Solubility increases down the group. $Mg(OH)_2$ is sparingly soluble, whereas $Ba(OH)_2$ is significantly more soluble.
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What is the trend in solubility for Group 2 sulfates, $MSO_4$?
Solubility decreases down the group. $MgSO_4$ is soluble, but $BaSO_4$ is insoluble.
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Why is barium sulfate ($BaSO_4$) used in 'barium meals' for medical imaging?
It is insoluble in water and body fluids, making it non-toxic. It is also opaque to X-rays, allowing it to outline the digestive tract.
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What is the trend in thermal stability for Group 2 carbonates ($MCO_3$)?
Thermal stability increases down the group. More energy (a higher temperature) is required to decompose them.
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Explain why the thermal stability of Group 2 carbonates increases down the group.
Down the group, the cation's ionic radius increases, so its charge density decreases. This reduces its polarising power, so it distorts the electron cloud of the carbonate ion less, making the compound more stable.
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Write the general equation for the thermal decomposition of a Group 2 nitrate.
$2M(NO_3)_2(s) \rightarrow 2MO(s) + 4NO_2(g) + O_2(g)$. Brown fumes of $NO_2$ are observed.
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A white solid, X, dissolves in water to form a solution with a pH of 11. Adding dilute sulfuric acid produces a white precipitate. What is X?
Calcium hydroxide, $Ca(OH)_2$. It's alkaline (pH 11) and forms insoluble calcium sulfate, $CaSO_4$ (a white precipitate), with sulfuric acid.