Question

An element ‘A’ has atomic number 11, name the period and group number to which it belongs.

Answer 1

The element can be identified with the help of electronic configuration as we are already given with the atomic number. The electronic configuration will give an idea about the number of valence electrons and further we can know the group and period number.

Complete step by step answer:
Let us first write down the electronic configuration of element A with atomic number 11.
Electronic configuration is $1{s^2}2{s^2}2{p^6}3{s^1}$
As we know that to complete the s shell we require two electrons but here there is only one electron in the 3s shell so the number of valence electrons is 1.
Now, the valence electrons help us to know about the group number in the periodic table. The number of valence electrons in the outermost shell is equal to the group number. Thus, the group number of element A is 1.
To identify the period number we need to know the highest principal quantum number. It means that the valence shell in which the last electron enters according to the electronic configuration.
So, here the last electron enters in the 3s shell. Thus, the period number of an element A is 3.
In the last, we can conclude that the group of an element A is 1 and period is 3.
It belongs to period 3 and group 1A in the modern periodic table.

Note: Aufbau principle is used to write the electronic configuration of an element A. So, the sequence of shells must be correct. We studied the term valence electrons in this question. Valence electrons are the electrons which are present in the outermost shell of an atom. The term valency is the number of electrons which is required to determine whether loss or gain to attain the stability of a shell or it can be termed as to complete the octet of an atom.