Question

The relative atomic masses of two isotopes of an element are 15.9936 and 17.0036 amu. Calculate (A) the number of electrons (B) the number of protons (C) the number of neutrons (D) mass number. Also mention the quantum numbers of valence electrons.

Answer 1

Hint: We have to calculate the atomic number from the atomic mass. The atomic number is calculated by dividing the atomic mass by two. From the atomic number, we can calculate the number of protons and electrons. From the number of protons and mass number, we can calculate the number of neutrons. The quantum number of valence electrons includes principal quantum number, azimuthal quantum number, magnetic quantum number and spin quantum number.

Complete step by step answer:
Given data contains,
Relative atomic masses of two isotopes are 15.9936 and 17.0036 amu.
We can calculate the atomic number by dividing the atomic mass by two.
Atomic number = $\dfrac{{{\text{Atomic mass}}}}{2}$
Atomic number=$\dfrac{{15.9936}}{2}$
Atomic number = $8$
The atomic number of elements is $8$.
The total number of the protons and neutrons present inside the nucleus is known as mass number.
The number of protons present in the nucleus is the atomic number.
For an element ${\text{E,}}$ the top left number represents the mass number and the bottom left number represents the atomic number.

The letter A represents mass number.
The letter Z represents atomic numbers.
Isotopes of elements contain the same number of protons but variation is seen in the different number of neutrons.
We can give the number of protons as,
The number of protons in the nucleus is equal to the atomic number of an atom.
The atomic number of elements is 8.
The number of protons in an element is 8.
We know that the number of protons present in the nucleus is equal to the number of electrons orbiting around the nucleus.
The number of protons of an element is 8, so the number of electrons is also 8.
The mass number of isotopes (1) is 16.
The mass number of isotopes (2) is 17.
We can calculate the number of neutrons present in the element by subtracting the mass number from the number of protons.
We can write the expression to determine the number of neutrons as,
Number of neutrons = ${\text{Mass number}} - {\text{Number of protons}}$
Number of neutrons in isotope of lower atomic mass is calculated as,
Number of neutrons = ${\text{Mass number}} - {\text{Number of protons}}$
Number of neutrons = ${\text{16 - 8}}$
Number of neutrons = $8$
The number of neutrons in the isotope of lower atomic mass is 8.
Number of neutrons in isotope of higher atomic mass is calculated as,
Number of neutrons = ${\text{Mass number}} - {\text{Number of protons}}$
Number of neutrons = ${\text{17 - 8}}$
Number of neutrons = $9$
The number of neutrons in the isotope of lower atomic mass is 9.
The valence shell could contain four electrons
In the $2p$, the principal quantum number n will have value as $2$. The value of azimuthal quantum number l will be \[1\], the value of magnetic quantum number will be \[ + 1,0, - 1\] and the spin quantum number will have value $ + \dfrac{1}{2}$ (or) $ - \dfrac{1}{2}$.
In the $2p$, the principal quantum number n will have value as $2$. The value of azimuthal quantum number l will be \[0\], the value of magnetic quantum number will be \[0\] and the spin quantum number will have value $ + \dfrac{1}{2}$ (or) $ - \dfrac{1}{2}$.

Note: Let us take an example of an element with atomic number 12, the number of protons and electrons present in the element would also be 12. Every element in the periodic table will have a different number of protons. Since an atom contains the same number of protons and electrons, we can say an atom is neutral in terms of electrical charge. The atomic number of the element is written front and slightly below the symbol of the element.
Example: For the given element ${}_2^4He$, the atomic number is two and the number of protons and electrons present in the element is also two.