(II) What are the atomic numbers of elements whose outermost electrons are represented by (a) $3 s^{1}$ (b) $2 \mathrm{p}^{3}$ and (c) $3 p^{5} ?$

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(II) What are the atomic numbers of elements whose outermost electrons are represented by (a) $3 s^{1}$ (b) $2 \mathrm{p}^{3}$ and (c) $3 p^{5} ?$

CBSE | Chemistry | Class 11 | NCERT | Structure of Atom

(II) What are the atomic numbers of elements whose outermost electrons are represented by (a) $3 s^{1}$ (b) $2 \mathrm{p}^{3}$ and (c) $3 p^{5} ?$

(II) (a) $3 \mathrm{~s}^{1}$
Complete electronic configuration: $1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 \mathrm{p}^{6} 3 \mathrm{~s}^{1}$
Total no. electrons in the atom $=2+2+6+1=11 \quad \therefore$ the element’s atomic number is 11
(b) $2 \mathrm{p}^{3}$
Complete electronic configuration: $1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 \mathrm{p}^{3}$
Total no. electrons in the atom $=2+2+3=7$
$\therefore$ the element’s atomic number is 7
(c) $3 p^{5}$
Complete electronic configuration: $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{5}$
Total no. electrons in the atom $=2+2+6+2+5=17$
$\therefore$ the element’s atomic number is 17