Ncert Solutions Chemistry Class 11th

Due to small size, the ionization enthalpies of Be and Mg are much higher than those of other alkaline earth metals. Therefore, a large amount of energy is needed to excite their valence electron, and that's why they do not impart colour to the flame.

Different concentrations of alkali metals in liquid ammonia gives different colours. The dilute solutions impart blue colour due to presence of ammoniated electrons whereas the concentrated solutions have copper bronze colour as  ammoniated metal ions are bound by free electrons.

Potassium and caesium have much lower ionization enthalpy than that of lithium. As a result, these metals easily emit electrons on exposure to light. Due to this, K and Cs are used in photoelectric cells rather than lithium.

Alkali and alkaline earth metals are reducing agents. That is why these metals are not obtained by chemical reduction methods.

Both lithium and magnesium are harder and lighter than other elements in the respective groups.

Lithium and magnesium react slowly with water. Their oxides and hydroxides are much less soluble and their hydroxides decompose on heating. Both form a nitride, Li₃N and Mg₃N₂, by direct combination with n

(i) Ionization enthalpy. Because of high nuclear charge the ionization enthalpy of alkaline earth metals are higher than those of the corresponding alkali metals.

(ii) Basicity of oxides. Basicity of oxides of alkali metals are higher than that of alkaline earth metals.

(iii) Solubility of hydr

It is because ionization enthalpy? H_i of potassium = 419 kJ mol^-1. Ionization enthalpy of sodium = 496 KJ mol^-1. Since Ionization enthalpy of potassium is less than that of sodium, potassium is more reactive than sodium.

Let x be the oxidation state of Na in Na₂O₂     

Then, 2x + 2 (-1) = 0  

=>2x – 2 = 0  

=> x =  +1.

All the alkali metals have one valence electron, ns1 outside the noble gas core. The loosely held s-electron in the outermost valence shell of these elements makes them the mostelectropositive metals, i.e. they readily lose electron to give monovalent M+ ions. Hence, they are never found in free sta

The general characteristics and gradation in properties of alkaline earth metals are:

• Atomic size goes on increasing down the group.
• Ionisation energy goes on decreasing down the group.
• They are harder than alkali metals.
• They are less electropositive than alkali metals.

Electropositive character increas