Class 10 MAHARASHTRA STATE TEXTBOOK BUREAU Solutions Science Chapter 2 - Periodic Classification of Elements

1. The number of electrons in the outermost shell of alkali metals is 1.

1. Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in Group 2.

1. Molecular formula of the chloride of an element X is XCl. This compound is a solid having high melting point. Sodium (Na) present in the same group as X.

(ii) P-block elements are non-metals.

1. Atomic number: 12
2. Group 2
3. Period 3
4. Beryllium (4) is the element which resembles to the given electronic configuration.

Electronic configuration of the following elements is:

₃Li = 2,1

₁₄Si = 2,8,4

₁₁Na = 2,8,1,

₁₅P = 2,8,5

₁₄Si, ₁₅P belong to the third period because according to their electronic configuration , each element contains three shell i.e. K, L, M.

Electronic configuration of the following elements is:

₁H (1)

₇N (2, 5)

₂₀Ca (2, 8, 8, 2)

₁₆S (2, 8, 6)

₄Be (2, 2)

₁₈Ar (2, 8, 8)

Elements belongs to the 2nd group: ₄Be and ₂₀Ca.

Electronic configuration of the following elements is:

₇N=2,5

₆C=2,4

₈O=2,6

₅B=2,3

₁₃Al =2,8,3

The most electronegative element is ₈O as electronegativity decreases down a group while it increases moving across a period from left to the right.

Electronic configuration of the following elements is:

₄Be=2,2

₆C=2,4

₈O=2,6

₅B=2,5

₁₃Al=2,8,3

The most electropositive element is ₁₃Al electropositivity increases down a group while it decreases moving across a period from left to the right.

Electronic configuration of the following elements is:

₁₁Na=2,8,1

₁₅P=2,8,5

₁₇Cl=2,8,7

₁₄Si=2,8,4

₁₂Mg=2,8,2

The element which has the largest atom is ₁₁Na because atomic size decreases moving across a period from left to the right.

Electronic configuration of the following elements is:

₁₉K=2,8,8,1

₃Li=2,1

₁₁Na=2,8,1

₄Be=2,2

The element with the smallest atomic radius is ₄Be because atomic size decreases moving across a period from left to the right while it increases down a group.

Electronic configuration of the following elements is:

₁₃Al=2,8,3

₁₄Si=2,8,4

₁₁Na=2,8,1

₁₂Mg=2,8,2

₁₆S=2,8,6

The element with the highest metallic character is ₁₁Na as metallic character decreases moving across a period from left to the right.

Electronic configuration of the following elements is:

₆C=2,4

₃Li=2,1

₉F=2,7

₇N=2,5

₈O=2,6

The element with the highest nonmetallic character is ₉F as nonmetallic character increases moving across a period from left to the right

1. The atom having the smallest size is Hydrogen (H).
2. The atom having the smallest atomic mass is Hydrogen (H).
3. The most electronegative atom is Fluorine (F).
4. The noble gas with the smallest atomic radius is Helium (He).
5. The most reactive nonmetal is Fluorine (F).

Mendeleev's Periodic Law: The physical and chemical properties of elements are a periodic function of their atomic masses.

1. There are eight vertical columns called groups. They are numbered from I to VIII. Groups I to VII are further divided into two subgroups A and B.
2. All the elements of a sub-group have similar properties and show same valency, which is equal to the group number.
3. There are seven horizontal rows, known as periods. They are numbered from 1 to 7. As one moves from left to right in a period, there is a gradual change from metallic to non-metallic properties.

Structure of the modern periodic table:

The physical and chemical properties of elements are the periodic functions of their atomic numbers.

Main features of the Modern Periodic Table:

1. The modern periodic table contains 7 horizontal rows called periods and 18 vertical columns called groups.
2. Apart from the seven rows, there are two additional rows placed separately at the bottom of the table.
3. The entire table is divided into four blocks-s-block, p-block, d-block and f-block.
4. The modern periodic table is also called the Long Form of the Periodic Table.
5. The similar properties which recur after a regular interval are called periodic properties.

Position of isotopes in the Mendeleev's and the modern periodic table.

• Periodic table is based on atomic number. Since, all hopes of an element have same atomic number, they have not given any specific position.
• Isotopes are atoms of the same element having different atomic mass but same atomic number. For e.g., there are three isotopes of hydrogen with atomic mass 1, 2, and 3. According to Mendeleev's periodic table these should be placed at three separate places. However isotopes have not been given separate places in the periodic table.

1. As we go from left to right in a period, the atomic size or atomic radius increases with increase in atomic number. Increase in atomic number leads to an increase in the number of protons and electrons in the atoms. Due to the large nuclear charge (positive charge on the nucleus), the electrons are pulled in more close to the nucleus and the size of atom decreases.

1. As the effective nuclear charge acting on the valence shell electrons increases across a period, the tendency to lose electrons will decrease. Hence, metallic character decreases across a period.

1. Atomic size increases as we go down a group because each time one new shell is added and electrons in the outermost shell move away from the nucleus.

1. The valency of an element is determined by the valence electrons. Hence, elements belonging to the same group have the same valency.

1. According to the 2n² rule, the maximum number of electrons in the third period = 2 x (3)² = 18. But, the last shell cannot accommodate more than 8 electrons so, the number of electrons in third period is 8. Hence, the number of elements is also 8.

1. Period 3
2. Group 18
3. Halogen family
4. Alkali metals
5. Alkaline earth metals
6. Boron( second period), Silicon (third period)
7. Sulphur and Chlorine
8. Carbon and Silicon