IMPORTANT QUESTIONS OF PERIODIC CLASSIFICATION OF ELEMENTS #CLASS10#TERM2 BOARD EXAMS UP/CBSE/ICSE

1-periodicity-The repetition of same properties after definite interval is called periodicity in properties.

2-Mendeleev’s periodic law-Properties of elements are the periodic functions of their atomic masses.

3-limitations of Mendeleev’s classification*Position of hydrogen was not justified.

*Increasing order of atomic mass could not be maintained.

*Isotopes have similar chemical properties but different atomic masses, they cannot be given separate places.

The metallic character of elements change along a period of the periodic table from the left to the right--

-The metallic character goes on decreasing along a period from left to right because atomic size goes on decreasing therefore, tendency to lose electrons decreases.

2*the valency of elements vary

(a) in going down a group-Valency remains the same
(b) in going from left to right in a period-

Valency first goes on increasing from left to right in a period till middle of period, then decreases.

3*the tendency of atoms to lose electrons change on going from

left to right across a period-decreases from left to right across a period.

 top to bottom in a group-Tendency to lose electrons increases from top to bottom in a group.

4*

1. Elements in a group have similar chemical properties-Elements in a group have same number of valence electrons and same valency therefore have similar chemical properties.
2. Elements of Group I form ions with a charge of +1- It is because elements of group 1 lose one electron to acquire +1 charge and become stable.

5*Number of shells of elements as we go down a group-Different elements in same group have same number of valence electrons

*Number of shells of elements in the same period.-Number of shells of elements in same period are equal.

*

Number of shells of elements as we go down a group-

Number of shells of elements

goes on increasing down the group.

*Number of valence electrons of elements on moving from , left to right in a period.- Number of valence electrons of elements goes on increasing on moving from left to right in a period, e.g. lithium has 1, beryllium has 2, boron has 3, carbon has 4, nitrogen has 5, oxygen has 6, fluorine has 7 and neon has 8 valence electrons.

*Atomic size down a group-Atomic size goes on increasing down a group.

Some important previous year questions:

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