Practice is considered as the most powerful key to learn Chemistry. Solving practice problems, working on equations and formulas should be a core feature of your daily study routine. Reviewing and working the practice problems will help you test your understanding and knowledge of chemistry. And when you talk about solving a variety of practice problems, nothing can be better that the questions given in the NCERT Textbooks.
To help students find the right approach to all the NCERT questions, we are providing detailed and accurate solutions here. These solutions will help you know the right explanation for each NCERT question and understand the technique to write perfect answers in the annual examinations.
In this article we are providing the NCERT solutions for Class 11 Chemistry chapter 10, The s-Block Elements. These solutions will make it easy for you to prepare easily and effectively for the annual exams.
Main topics discussed in Class 11 Chemistry chapter- The s-Block Elements are:
- Group 1 elements: alkali metals
- General characteristics of the compounds of the alkali metals
- Oxides and hydroxides
- Halides
- Salts of oxo-acids
- Anomalous properties of lithium
- Some important compounds of sodium
- Biological importance of sodium and potassium
- Group 2 elements : alkaline earth metals
- General characteristics of compounds of the alkaline earth metals
- Anomalous behaviour of beryllium
- Some important compounds of calcium
- Biological importance of magnesium and calcium.
CBSE Class 11 Chemistry Syllabus 2018 - 2019
Some of the questions and their solutions from NCERT Solutions for Class 11: The s-Block Elements, are as follows:
Q. What are the common physical and chemical features of alkali metals?
Sol. Physical properties of alkali metals:
(i) Alkali metals have low ionization energies because due to their large size the outermost electron is far away from the nucleus and can be easily removed. The ionization energies of alkali metals decrease on moving down the group.
(ii) Alkali metals are soft and light with silvery white appearance.
(iii) Their densities are low because of the large atomic sizes. The density increases down the group with the only exception that potassium has lower density than that of sodium.
(iv) They have low melting and boiling points due to the weak metallic bonding present in them.
(v) Alkali metals and their salts impart a characteristic colour to the flame. This is because the heat from the flame excites the valence electron from lower to higher energy level. When an excited electron jumps back to the ground state, it emits excess energy in the form of radiations that fall in the visible region.
Q. Discuss the general characteristics and gradation in properties of alkaline earth metals.
Sol. Atomic properties of alkaline earth metals:
(i) The general electronic configuration of alkaline earth metals is [noble gas] ns2.
(ii) The atomic and ionic radii of alkaline earth metals are smaller than that of alkali metals. On moving down the group their atomic and ionic radii increase due to the decrease in their effective nuclear charge.
(iii) These metals lose two electrons to acquire the nearest noble gas configuration. Therefore, their oxidation state is +2.
(iv) Due to their small size, the first ionization enthalpies of alkaline earth metals are higher than those of the alkali metals. But their second ionization enthalpies are found to be lower than those of the corresponding alkali metals.
Q. Why are alkali metals not found in nature?
Sol. The alkali metals have only one electron in their valence shell, which they can lose easily to complete their octet. Thus the low ionization energies and high electropositive character cause these metals to be highly reactive hence, preventing them to exist in free state in nature. They are found in the earth’s crust in the form of halide, sulphate, carbonate, silicate, borate, oxide ores, etc.
Q. Explain why is sodium less reactive than potassium.
Sol. The ionisation enthalpy of the alkali metals decreases down the group. Hence the ionisation enthalpy of potassium is lower than that of sodium which makes it more electropositive and stronger reducing agent as compared to sodium. Therefore, sodium is less reactive than potassium.
Download all the NCERT solutions for Class 11: The s-Block Elements, from the following link: