Ncert Solutions Chemistry Class 11th

3.7.  (i) Lawrencium (Lr) with atomic number (z) = 103

(ii) Seaborgium (Sg) with atomic number (z) = 106.

3.6. The element is chlorine (Cl) with atomic number (Z) = 17.

3.5. Elements with atomic numbers from Z = 87 to Z = 114 are present in the 7th period of the periodic table. So, this elements lies in the Period – 7 and Group -14 of Block-p.

3.4. The sixth period means that the highest principal quantum number = 6. The subsequent periods comprise of 8, 18, 18 and 32 elements in the same order. The sixth period comprises of 32 elements where electrons enter the 6s, 4f, 5d and 6p orbitals. Number of orbitals present in 6s=1. 4f= 7, 5d= 5 and 6p= 3. The total number of orbitals is 16. A total of 32 electrons can be filled in these 32 orbitals; therefore, the sixth period should have a maximum of 32 elements.

3.3. Mendeleev's periodic law classifies the elements based on their atomic weight. Modern periodic law classifies the elements based on their atomic number.

3.2. Mendeleev arranged the elements horizontally, in periods and vertically, in groups in the increasing order of their atomic masses. This classification was done in such a way that the elements with similar properties fall in the same group.

3.1. The basic theme of organisation of elements in the periodic table is to simplify, systematize and classify the elements based on their similarities in properties. This arrangement makes it easier for us to group the elements and makes it less confusing to present the periodic table.

1.51. In 1808, Dalton published 'A New System of Chemical Philosophy', in which he proposed the following:

1. Matter consists of indivisible atoms.

2. All atoms of a given element have identical properties, including identical mass. Atoms of different elements differ in mass.

3. Compounds are formed when atoms of different elements combine in a fixed ratio.

4. Chemical reactions involve reorganisation of atoms. These are neither created nor destroyed in a chemical reaction.

1.50. Carbon-12 isotope is the most abundant isotope of carbon and has been chosen as the standard. Since C-12 is used as the standard atom, one atomic mass unit is defined as one-twelfth of the mass of one carbon – 12 atoms. This is because it has an equal number of protons and neutrons (6) and makes up the majority of matter.

1.49. The empirical mass of ethene is half of its molecular mass. The empirical formula represents the simplest whole-number ratio of various atoms present in a compound.

Molecular Formula = n * Empirical formula

Empirical formula of Ethene = C₂H₄

Empirical Formula Mass = 14 amu= ½ Molecular Mass of Ethene

The ratio of Carbon and Hydrogen in the empirical formula is 1: 2.