Question

what is the basis of modern periodic table?why lithium with atomic number3and potassium with atomic no 19 are placed in group1?what will be the atomic numbers of the first two elements in second group​

Answer 1

In the modern periodic table;

• atoms are arranged on the basis of increasing atomoic number
• repetition of property
• grouping elements with same valency

Li and K are placed in same group 1 because they have the same valency of +1.

Atomic numbers of

• 1st element of group 2 = Be => 4
• 2nd element of group 2 = Mg => 12

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