Question

Correct order of atomic radius is:
(A) V > Ti
(B) Cl > S
(C) Cs > Rb
(D) Ne > Be

Answer 1

Hint: In a periodic table as we move from left to right the effective nuclear charge increases and so the size decreases. While from top to bottom the number of shells increases and so the size increases. In d-block along a period the atomic size first increases then decreases.

Complete step by step answer:
-First we will see what atomic radius is.
Atomic radius basically refers to the distance between the centre of the nucleus of an atom and its outermost shell or upto the point where the electron density cloud is maximum.
-Now we will talk about the trends of atomic radius in the periodic table.
Along a period (from left to right) in a periodic table: The shell number remains the same but the number of electrons increases. The effective nuclear charge increases and hence the size decreases.
Down the group (from top to bottom) in a periodic table: The shell number increases as we move from top to bottom. With increase in shell number the size also increases as we go down the group.
-We will now check the options to see which of the options shows the correct sequence of atomic radius.
For (A) V > Ti : Both these elements lie in the d-block and in a d-block the size of elements first increases, then decreases. Vanadium (V) has an atomic number of 23 while Titanium has an atomic number of 22. So, the size of V < Ti.
This option is also false.

For (B) Cl > S : In a periodic table as we move from left to right, the size decreases due to increasing effective nuclear charge. Hence the size of S > Cl.
This option is also false.

For (C) Cs > Rb : From top to bottom the size increases due to increase in the shell number. Hence the size of Cs > Rb.
Hence this option is correct.

For (D) Ne > Be : In a periodic table as we move from left to right, the size decreases due to increasing effective nuclear charge. Hence the size of Be > Ne.
This option is also false.

-So, the correct option will be: (C) Cs > Rb

Note: The atomic radius is of 3 types: covalent radius, Van der Waals radius and metallic radius.
1) Covalent radius : It is half of the distance between the nucleus of 2 covalently bonded atoms.
2) Van-der Waals radius: It is half of the distance between the nucleus of 2 isolated atoms which are not bonded to each other but are attracted to each other via Van-der Waal force of attraction.
3) Metallic radius: It is the half of the distance between 2 adjacent metal ions in a metal lattice or we can say the force of attraction between the mobile electrons and the positive kernels.