Question

The positions of eight elements in the Modern Periodic Table are given below where atomic numbers of elements are given in the parenthesis. Period No.
2
Li (3)
Be (4)
3
Na (11)
Mg (12)
4
K (19)
Ca (20)
5
Rb (37)
Sr (38)
(i) Write the electronic configuration of Ca.
(ii) Predict the number of valence electrons in Rb.
(iii) What is the number of shells in Sr?
(iv) Predict whether K is a metal or a non-metal.
(v) Which one of these elements has the largest atom in size?
(iv) Arrange Be, Ca, Mg and Rb in the increasing order of the size of their respective atoms.

Answer 1

Modern Periodic Table

Explanation:

1. Electronic configuration of Calcium (Ca) is 1s2 2s2 2p6 3s2 3p6 4s2.
2. Rubidium (Rb) has one valence electron in the outermost (5s1) shell.
3. Strontium (Sr) has 5 shells, the outermost shell (5s2) has 2 electrons.
4. Potassium (K) is a silvery-white metal, but soft enough to be cut with a knife with little force.
5. Rubidium (Rb) has the largest atom among the given elements.
6. Be, Mg, Ca and Rb -- this is the increasing order of size of atoms of these elements. Be is the smallest and Rb is the largest as atomic radii increases as we move down the periodic table.