Question

If an atom ‘A’ has atomic number 19 & mass number 39, state-

i) its electronic configuration

Answer 1

• An atomic number is a representation of the number of protons or electrons present in a neutral atom. It is represented by ‘Z’.
• Valence electron: The number of electrons present in the outermost shell of an atom is called valence electrons.

Explanation of an electronic configuration of an atom:

• Electronic configuration is the distribution of electrons in electronic shells.
• The formula ($2{\mathrm{n}}^2$) gives the maximum number of electrons in the shell, where n is the shell (orbital) number.
• In each shell, the maximum number of electrons is as follows: Two electrons will be in the first K shell.
• The 2nd L- Shell can accommodate 8 electrons.
• The number of electrons in a third shell is equal to 18 according to the Bohr-Bury scheme formula ( ) and so on.
• Also according to the Aufbau principle electrons are filled into energy levels in increasing order.
• Thus K-shell is near to nucleus should be filled first and then the second L-Shell and so on.
• The electronic configuration of the atom ‘A’ has an atomic number of 19 in electronic shells is as;
• K=2,L=8, M=8,N=1.
• The name of this atom "A" represents the potassium element in a modern periodic table.
• The mass number is represented by a superscript ₁₉${\mathrm{A}}^{39}$, equal to the total number of protons and neutrons.
• The number of protons is equal to 19= atomic numbers.
• Number of neutrons(n)=Mass number(A) - Atomic number (Z).
• n = 39-19
• n = 20.