Question

How does the valency vary in a period on gong the valency vary in a period on going from left to right?

Answer 1

The periodic table is defined as a tabular array of the chemical elements that maintains elements arranged in atomic number. It starts from the lowest atomic numbered element, hydrogen, to the element with the highest atomic number, oganesson. The number of protons present in the nucleus of an atom of that element is defined as the atomic number of an element.

Complete Solution :
A periodic table consists of seven horizontal rows and 18 vertical groups.
We know that an electron in an atom is characterised by a set of four quantum numbers (n, I, m and s) where the principal quantum number (n) defines the main energy level known as the shell. We have also studied about the filling of electrons into different subshells (s, p, d and f) in an atom. This distribution of electrons into various subshells of an atom is called its electronic configuration. The location of any element in the periodic table is reflected by the quantum numbers of the last orbital filled. Here we will discuss the direct relation between the electronic configuration of the element and its location in the periodic table.
When we move from left to right in a periodic table the valency increases.

Note: The period gives an indication the value of n for the outermost or valence shell. In other words, a successive period in the periodic table is associated with the filling of the next higher principal energy level like n = 1, n = 2, n = 3..... refers to the filling of the first, second, third and higher principal energy levels. It can be readily observed that the number of elements in each period is double the atomic orbitals that are present in the energy level that is being filled.