Chemistry Standard 11 Vol I>Chapter -1 - Alkali and Alkaline Earth Metals>EVALUATION>Q 21

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11th Tamil Nadu Board

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Which of the following statement is false?

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Important Points to Remember in Chapter -1 - Alkali and Alkaline Earth Metals from Tamil Nadu Board Chemistry Standard 11 Vol I Solutions

1. The s-block elements:

(i) Elements in which the last electron enters the s-orbital are called s-block elements. The elements of group-1 (alkali metals) and group-2 (alkaline earth metals) constitute s-block elements. The elements of these groups contain one or two electrons in their outermost s-orbital.

(ii) The electronic configuration of group-1 (alkali metals) may be represented as [Noble gas] ${ns}^{1}$ while that of group-2 (alkaline earth metals) may be represented as [Noble gas] ${ns}^{2}$ where n is the number of outermost shell.

2. Alkali metals:

(i) The group-1 elements are lithium, sodium, potassium, rubidium, caesium and francium.

(ii) Lithium is the lightest metal.

(iii) Lithium shows diagonal relationship with $Mg$ . Sodium is the most abundant alkali metal in the earth crust.

(iv) Alkali metals have lowest ionization enthalpies and largest atomic radii in their respective periods.

(v) The hydration enthalpies of alkali metal ions are in the order

$L i^{+} > N a^{+} > K^{+} > R b^{+} > C s^{+}$

(vi) Alkali metals behave as strong reducing agents due to their low ionization enthalpies.

(vii) All alkali metals impart characteristic colour to the flame. $Li$ —caramine red, $Na$ —golden yellow, $K$ —pale violet, $Rb$ —reddish violet and $Cs$ —sky-blue. Caesium, due to its very low ionization enthalpy, is used in photoelectric cells.

(viii) Alkali metals, due to their large atomic radii, have very weak metallic bond. That is why they are soft and can be cut with the help of a knife.

(ix) The reactivity of alkali metals increases from lithium to caesium. Alkali metal hydrides are ionic in nature and are strong reducing agents.

(x) Lithium forms normal oxide, $L i_{2} O$ even with excess of oxygen. $Na$ forms peroxide while $K, Rb$ and $Cs$ form superoxides on reaction with excess oxygen.

(xi) The basic character of alkali metal hydroxides increases on descending the group: $L i O H < N a O H < K O H < R b O H < C s O H$

(xii) Alkali metals dissolve in liquid ammonia giving deep blue solutions due to presence of ammoniated cations and ammoniated electrons.

(xiii) Lithium exhibits anomalous behaviour due to its small size, high ionization enthalpy and greater polarizing power.

(xiv) Sodium carbonate (washing soda), $N a_{2} C O_{3} . 10 H_{2} O$ is prepared by Solvay ammonia process.

(xv) Sodium hydroxide is manufactured by electrolysis of brine in Castner-Kellner Cell.

3. Alkaline earth metals:

The group-2 elements are beryllium, magnesium, calcium, strontium, barium and radium.

Calcium is the most abundant element of group-2. Ionization enthalpies of group-2 elements are larger than those of group-1 elements.

Hydration enthalpies of group-2 elements are in the order:

$B e^{2 +} > M g^{2 +} > C a^{2 +} > S r^{2 +} > B a^{2 +}$

The metallic bond in alkaline earth metals is stronger than in alkali metals. As a consequence, they are harder, have higher melting points and higher densities as compared to those of alkali metals.

Be and Mg do not impart colour to the flame because their valence electrons cannot be excited by the energy of the flame.

The solubility and basic character of hydroxides increases in the order:

$B e {(O H)}_{2} < M g {(O H)}_{2} < C a {(O H)}_{2} < S r {(O H)}_{2} < B a {(O H)}_{2}$

Thermal stability of carbonates is in the order:

$M g C O_{3} < C a C O_{3} < S r C O_{3} < B a C O_{3} < B e C O_{3}$

Solubility of sulphates is in the order: $M g S O_{4} > C a S O_{4} > S r S O_{4} > B a S O_{4}$

Beryllium exhibits diagonal relation with aluminium.

Calcium oxide (lime) and calcium carbonate $({CaCO}_{3})$ are two important compounds of calcium.

The raw material required for manufacture of cement are lime, clay and gypsum.

${Na}^{+}, K^{+}, {Mg}^{2 +}$ and ${Ca}^{2 +}$ ions are present in large proportions in biological fluids. These ions perform important biological functions such as maintenance of ion balance and transmission of impulses along nerve fibres.

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