Atomic size means radius of an atom. Hema, when read this statement u

1.	Atomic size means radius of an atom. Hema, when read this statement understood that it is the distance between centre of nucleus and the outermost shell (valence shell) of an isolated atom. She also came to know that atomic size generally increases from top to bottom in a group, due to addition of a new shell and decrease along a period from left to right, due to increase in nuclear charge which pulls the electrons towards it. (i) Hema has to arrange the following elements in an increasing order in a group in accordance of their atomic size Li,Rb, K, Cs, Na.(ii) Atomic number is considered to be a more appropriate parameter than atomic mass for classification of elements in a periodic table' Give any two reasons to justify the statement
Answer» (i) Elements arranged in an increasing order in a group are : Li, Na, K, Rb, Cs. (ii) (a) Although most of the elements were placed in the order of increasing atomic masses, increasing order could not be maintained in all cases. (b) There was no place for isotopes in Mendeleev's periodic table, although they differ in atomic mass.

Atomic size means radius of an atom. Hema, when read this statement understood that it is the distance between centre of nucleus and the outermost shell (valence shell) of an isolated atom. She also came to know that atomic size generally increases from top to bottom in a group, due to addition of a new shell and decrease along a period from left to right, due to increase in nuclear charge which pulls the electrons towards it. (i) Hema has to arrange the following elements in an increasing order in a group in accordance of their atomic size Li,Rb, K, Cs, Na.(ii) Atomic number is considered to be a more appropriate parameter than atomic mass for classification of elements in a periodic table' Give any two reasons to justify the statement

Answer»

(i) Elements arranged in an increasing order in a group are :

Li, Na, K, Rb, Cs.

(ii) (a) Although most of the elements were placed in the order of increasing atomic masses, increasing order could not be maintained in all cases.

(b) There was no place for isotopes in Mendeleev's periodic table, although they differ in atomic mass.