Question

Five atoms are labelled V to Z

Atoms	Mass number	Atomic Number
V	40	20
W	19	9
X	7	3
Y	16	8
Z	14	7

Which one of these atoms (1) contains 7 protons; (2) has an electronic configuration 2,7?

Answer 1

• Atomic number(Z)- The total number of protons in the nucleus of an atom gives us the atomic number of that atom.
• Protons are positively charged subatomic particles present in the nucleus of an atom.
• The electronic configuration of an element describes how electrons are distributed in its atomic orbitals.
• The electrons are filled in the increasing number of shells viz. K,L,M,N,etc.
• Number of electrons in a shell is given by 2n² where n is the number of shells.
• Putting n=1,2,3 and 4, we get the number of electrons 2,8,18,32 that can be filled in each shell respectively.

(1) Element Z has atomic number 7, hence it has 7 protons in its nucleus.

(2) To have electronic configuration 2,7 an element should have atomic number 9.

Element W has an electronic configuration 2,7.