Q1. - Organic Chemistry

Question

Question: While the most common isotope of nitrogen has a mass number of 14 (nitrogen-14), a radioactive isotope of nitrogen has a mass number of 13 (nitrogen-13). Nitrogen-13 is used in PET (positron emission tomography) scans by physicians to monitor brain activity and diagnose dementia. For each isotope, give the following information: (a) the number of protons; (b) the number of neutrons; (c) the number of electrons in the neutral atom; (d) the group number; and (e) the number of valence electrons.

Step-by-Step Solution

Answer

Answer

 

(a) The number of protons in nitrogen-13 and nitrogen-14 is 7 and 7, respectively.

 

(b) The number of neutrons in nitrogen-13 and nitrogen-14 is 6 and 7, respectively.

 

(c) The number of electrons in nitrogen-13 and nitrogen-14 is 7 and 7, respectively.

 

(d) The group number of nitrogen-13 and nitrogen-14 is 5A and 5A, respectively.

 

(e) The number of valence electrons nitrogen-13 and nitrogen-14 are 5A and 5A, respectively.

 

 

Step-by-Step Solution Step 1: Meaning of Isotopes

Isotopes are the species that only differ in the number of neutrons or atomic mass. The given isotopes are nitrogen-13 and nitrogen-14, respectively; both are the isotopes of nitrogen with different atomic masses

Step 2: Calculation of number of protons and electrons

The atomic number of the nitrogen is seven. Thus, the number of protons and electrons in nitrogen-13 and nitrogen-14 is 7 and 7, respectively.

Step 3: Calculation of number of neutrons

The atomic mass of nitrogen-13 is 13, whereas the atomic mass of another isotope is 14. Atomic mass represents the sum of the number of protons and neutrons. It is given by the  following formula:

$\mathrm{Atomic} \mathrm{Mass}= [\mathrm{Number} \mathrm{of} \mathrm{protons} + \mathrm{Neutrons}]$

The values for nitrogen-13 and nitrogen-14 are substituted in the above formula.

$\begin{array}{rcl}13 & =& 7 +Number of neutrons\\ & =& 13- 7\\ \mathrm{NUMBER} \mathrm{OF} \mathrm{NEUTRONS} & =& 6\end{array}$

Similarly, for nitrogen-14,

$\begin{array}{rcl}14 & =& 7 +\mathrm{Number} \mathrm{of} \mathrm{Neutrons}\\ \mathrm{Number} \mathrm{of} \mathrm{Neutrons}& =& 14 - 7\\ \mathrm{Number} \mathrm{of} \mathrm{Neutrons}& =& 7\end{array}$

 

The values for nitrogen-13 and nitrogen-14 are substituted in the above formula.

 

Step 4: Determination of group number and valence electrons

Both the isotopes of the nitrogen differ only in the number of neutrons. Nitrogen belongs to group 5A.

 

The electronic configuration of nitrogen is  $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^3$. The electrons found in the last shell or valence shell are known as valence shell electrons.

 

Thus, the valence shell electrons in nitrogen-13 and nitrogen-14 are 5 and 5, respectively