Understand most confusing terms of the chapter in a very easy method.
1
Partial covalent character of lithium compounds
The book mentions that the salts of alkali metals are the most known ionic salts.
On the other hand, lithium is an alkali metal, yet its compounds especially halides are partially covalent in nature.
This is because lithium ion has a small size and has the maximum tendency to distort the anionic electron cloud. This distortion of the electron cloud of a negative ion by a positive ion is known as polarisation. In turn, this results in increasing covalent character in lithium compounds.
The book mentions that the salts of alkali metals are the most known ionic salts.
On the other hand, lithium is an alkali metal, yet its compounds especially halides are partially covalent in nature.
This is because lithium ion has a small size and has the maximum tendency to distort the anionic electron cloud. This distortion of the electron cloud of a negative ion by a positive ion is known as polarisation. In turn, this results in increasing covalent character in lithium compounds.
2
All alkaline earth metals impart characteristic colour to the flame. No.
Alkaline earth metal salts impart characteristic colours to the flame except beryllium and magnesium.
But why? The answer lies in the difference in ionisation enthalpies of Be and Mg from the rest of the alkaline earth metals.
Generally, alkaline earth metals have low ionisation enthalpies. So, the valence electrons in these atoms can be easily excited to higher energy states by the flame of bunsen burner. When these excited electrons come back to the ground state they emit radiations which fall in the visible region. Therefore, they give colours to the flame.
Alkaline earth metal salts impart characteristic colours to the flame except beryllium and magnesium.
But why? The answer lies in the difference in ionisation enthalpies of Be and Mg from the rest of the alkaline earth metals.
Generally, alkaline earth metals have low ionisation enthalpies. So, the valence electrons in these atoms can be easily excited to higher energy states by the flame of bunsen burner. When these excited electrons come back to the ground state they emit radiations which fall in the visible region. Therefore, they give colours to the flame.
On the other hand, Be and Mg atoms are comparatively smaller and their ionisation enthalpies are very high. Hence, the energy of the flame is not sufficient to excite their electrons to higher energy levels. Therefore, these elements do not give any colour to the flame.
3
Potassium carbonate can be prepared by the Solvay Process. No
The textbook says that Sodium carbonate can be prepared by the Solvay process.
And it is natural to take this idea and assume that potassium carbonate can also be prepared by the Solvay process as they are both alkali metal carbonates. But this is a misconception.
is only sparingly soluble in water. So, when is passed through ammoniated brine, gets precipitated out and can be converted to by decomposition.
Now, being highly soluble in water, does not precipitate out when is passes through an ammoniated solution of potassium chloride and so, can not be precipitated. And therefore, we can not prepare by the Solvay process.
The textbook says that Sodium carbonate can be prepared by the Solvay process.
And it is natural to take this idea and assume that potassium carbonate can also be prepared by the Solvay process as they are both alkali metal carbonates. But this is a misconception.
is only sparingly soluble in water. So, when is passed through ammoniated brine, gets precipitated out and can be converted to by decomposition.
Now, being highly soluble in water, does not precipitate out when is passes through an ammoniated solution of potassium chloride and so, can not be precipitated. And therefore, we can not prepare by the Solvay process.
