Question

In modern periodic table, calcium (atomic number 20) is surrounded by elements with atomic number 12, 19, 21 and 38 Which of these having physical and chemical properties resembling calcium ? Which of these has largest atomic size and which has smallest atomic size ? Which of these has maximum tendency to lose elctron and why ?

Answer 1

Electronic configuration of elements with atomic numbers:

20 (Ca): [Ar] 4s2
12(Mg): [Ne] 3s2
19(K): [Ar] 4s1
21(Sc): [Ar] 3d1 4s2
38(Sr): [Kr] 5s2

1.       The outer electronic configuration of Mg. Ca and Sr shows that these elements belong to same group. Thereforem Mg and Sr will have physical and Chemical properties resembling calcium.
2.       Although the last electron in Sr enters 5s orbital, but on moving from Rb to Sr, the nuclear charge ncreases the thus atomic size of Sr gets smaller than K. Therefore, K has the largest atomic size and Mg has smallest atomic size since its last electron enters 3s orbital.
3.       K has only one electron in its outermost sub shell (4s) . By loosing this electron, will gain stable configuration of noble gas Ar. Therefore, K has the maximum tendency to loose electron.

Answer 2

Electronic configuration of elements with atomic numbers:

12 and 38