Question

STD 10 Maharashtra Board ( New syllabus)
Science L.2

Answer 1

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✔️ Mendeleev's Periodic law

The elements with physical and chemical properties are a periodic function of the atomic masses.


✔️ Structure of the modern periodic table -

1. In the modern periodic table, the elements are arranged by arranging in increasing atomic numbers.

2. There are total 7 horizontal rows called as periods and 18 vertical colomns ( 1 to 18 ) called as groups.

3. Each box represents the place for one element. Apart from these seven rows , there are two rows placed separately at the bottom of periodic table. They are lanthanides and actinide series.

4. There are altogether 118 elements in the modern periodic table.


✔️ Position of isotopes in the mendeleev's and the modern Periodic table

Isotopes were discovered long time after Mendeleev put forth the periodic table. A challenge was posed in placing isotopes in Mendeleev's periodic table,as isotopes have same chemical properties but different atomic masses. Later , the isotopes of Cl 17 - 35 and Cl 17 - 37 were placed in the same group as both have the same atomic numbers.

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