Alkaline Earth Metals MCQ - Practice Questions & Answers

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Alkaline Earth Metals(Chemical Properties) - 1, Alkaline Earth Metals(Chemical Properties) - 2 are considered the most difficult concepts.
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Alkaline Earth Metals(Physical Properties) - 1

Electronic configuration
These elements have two electrons in the s-orbital of the valence shell. Their general electronic configuration may be represented as [noble gas]ns². Like alkali metals, the compounds of these elements are also predominantly ionic.
Atomic and Ionic Radii
The atomic and ionic radii of the alkaline earth metals are smaller than those of the corresponding alkali metals in the same periods. This is due to the increased nuclear charge in these elements. Within the group, the atomic and ionic radii increase with the increase in atomic number.
Density
These metals are denser than alkali metals in the same period because these can be packed more tightly due to their greater nuclear charge and smaller size. The density decreases slightly upto calcium and then increases up to radium.
Melting and Boiling points
The melting and boiling points of these elements are higher than the corresponding alkali metals. This is due to the presence of two electrons in the valence shell and thus, strongly bonded in the solid-state. However, melting and boiling points do not show any regular trend because atoms adopt different crystal structures.
Ionisation energy
The alkaline earth metals have low ionization enthalpies due to fairly large size of the atoms. Since the atomic size increases down the group, their ionization enthalpy decreases. The first ionisation enthalpies of the alkaline earth metals are higher than those of the corresponding Group 1 metals. This is due to their small size as compared to the corresponding alkali metals. It is interesting to note that the second ionisation enthalpies of the alkaline earth metals are smaller than those of the corresponding alkali metals.
Electropositive or metallic character
The electropositive character of these elements increases down the group as the ionisation enthalpy value decreases.

Alkaline Earth Metals(Physical Properties) - 2

Oxidation states
The lattice energy increases as the charge on the ion increases. The increase in the lattice energy on account of the second electron from ns² is much more than the energy required to remove it. Thus, the stability of the +2 oxidation state is due to high lattice energy. Another reason, responsible for the +2 oxidation state is the hydration energy which is high for M²⁺ ions.
Flame colouration
In the case of Ca, Sr, Ba and Ra, the electrons can be excited by the supply of energy to higher energy levels. When the excited electrons return to the original level, the energy is released in the form of light. In beryllium and magnesium, the electrons are tightly held and hence excitation is rather difficult, thus do not show flame colouration.

Alkaline Earth Metals(Chemical Properties) - 1

Reaction with water
Calcium, strontium, barium and radium decompose cold water readily with evolution of hydrogen
$\mathrm{M\: +\: 2H_{2}O\: \rightarrow \: M(OH)_{2}\: +\: H_{2}}$
Magnesium decomposes boiling water but beryllium does not react with water, even when red hot, its protective oxide film survives even at high temperature as its oxidation potential is lower than the other members.
Reactivity towards atmosphere
Except beryllium, these metals are easily tarnished in air as a layer of oxide is formed on their surface. The effect of atmosphere increases as the atomic number increases. Barium in powdered form bursts into flame on exposure to air.
$\mathrm{M\: +\: air\: \rightarrow \: MO\: +\: M_{3}N_{2}}$
Reactivity towards acids
Like alkali metals, the alkaline earth metals freely react with acids and displace hydrogen.
$\mathrm{M\: +\: H_{2}SO_{4} \rightarrow \: MSO_{4}\: +\: H_{2}}$

Alkaline Earth Metals(Chemical Properties) - 2

Reaction with carbon
With the exception of Be, other metals when heated with carbon in an electric furnace or when their oxides are heated with carbon form carbides of the type MC₂. These carbides are called acetylides as on hydrolysis they evolve acetylene
$\mathrm{MC_{2}\: +\: 2H_{2}O\: \rightarrow \: M(OH)_{2}\: +\: C_{2}H_{2}}$
Solutions of metals in liquid ammonia
Like alkali metals, alkaline earth metals also dissolve in liquid ammonia to form coloured solutions. Dilute solutioins are bright blue in colour due to solvated electrons. These solutions decompose very slowly forming amides and evolving hydrogen. When the solution is evaporated, hexammoniate, M(NH₃)₆, is formed. These slowly decompose to givve amides.
$\mathrm{M(NH_{3})_{6}\: \rightarrow \: M(NH_{2})_{2}\: +\: 4NH_{3}\: +\: H_{2}}$
Reaction with hydrogen
Except beryllium, all combine with hydrogen directly to form hydrides of the type MH₂ when heated with hydrogen.
$\mathrm{M\: +\: H_{2}\: \rightarrow \: MH_{2}}$
BeH₂ and MgH₂ are covalent in nature while other hydrides are ioninc in nature. Calcium, strontium and barium hydrides liberate hydrogen at anode on electrolysis in the fused state. Ionic hydrides are violently decomposed by water eveolving hydrogen. CaH₂ is used for the production of hydrogen. The hydrides are food reducting agents.
$\mathrm{CaH_{2}\: +\: 2H_{2}O\: \rightarrow \: Ca(OH_{2})\: +\: 2H_{2}}$