Question

Elements X,Y,Z have atomic numbers 6,9 and 12 respectively.

Which one has 4 electrons in the outermost orbit.

Answer 1

• Let us first write the electronic configuration of elements X, Y and Z.
• 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.
• The 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.

Element X-

• The atomic number of Element X is 6.
• 2 electrons will fill the first shell i.e., the K shell.
• 4 electrons will fill the second shell i.e., the L shell.
• Hence, its configuration will be 2,4.

Element Y-

• The atomic number of Element Y is 9.
• 2 electrons will fill the first shell i.e., the K shell.
• 7 electrons will fill the second shell i.e., the L shell.
• Hence, its configuration will be 2,7.

Element Z-

• The atomic number of Element Y is 12.
• 2 electrons will fill the first shell i.e., the K shell.
• 8 electrons will fill the second shell i.e., the L shell.
• 2 electrons will enter the third shell i.e., the M shell.
• Hence, its configuration will be 2,8,2.

Hence, it is clear after writing the electronic configuration that element X has 4 electrons in its outermost orbit.