Question

What element is in period 4 and has 4 number shells and 3 valence electrons?

Answer 1

Hint: Try to attempt this question by the help of postulates of Bohr’s atomic model. See how many electrons are there in the first 3 shells according to this model and the fourth shell will be the valence shell which will have valence electrons. Do the summation of all the electrons so as to get the atomic number of the element.

Complete answer:
Let us first begin with discussion of postulates given by Bohr’s atomic model as follows:-
-In an atom, electrons revolve around the positively charged nucleus in a definite circular path called orbits or shells and each shell has a fixed energy and these circular orbits are also called as orbital shells or energy levels.
-These energy levels are represented by an integer (n =1, 2, 3…. so on) known as the principal quantum number. The orbits n=1, 2, 3, 4… are named as K, L, M, N…. shells and when an electron attains the lowest energy level i.e., K shell, it is said to be in the ground state.
-The number of electrons that can fit in:-
K shell = 2
L shell = 8
M shell = 18
N shell = 32 and so on
-As it is given that the element has 4 shells and the valence shell has only 3 electrons which means the first 3 shells have electrons according to the K, L and M shells.
So the total number of electrons present in this element is: 2 + 8 + 18 + 3 = 31 electrons.
 -As we know that for every element, its atomic number is equal to its number of protons or number of electrons present in the neutral state. So the atomic number of this element is 31.
-In the periodic table, the element of period 4 with atomic number 31 is: Gallium.

Note:
-For such types of questions, learn and understand all the atomic models and apply their postulates in order to obtain an answer.
-Try to learn periodic tables on a daily basis so as to answer these questions.