Question

The elements sodium to argon from period 3 of the periodic table. Which row describes the trend across period 3 from left to right of the following properties?
i)-Ionisation Enthalpy, ii)-Atomic Radii, iii)-Electronegativity
(A)- decreases, decreases, decreases
(B)- decreases, increases, decreases
(c)- increases, decreases, increases
(D)- increases, increases, increases

Answer 1

Hint: Ionization enthalpy of elements is the amount of energy or enthalpy required by an isolated gaseous atom to lose an electron in its ground state to ionize it. Atomic radius is the distance from the center of the nucleus to the outermost shell which contains electrons. This depends on the effective nuclear charge. Electronegativity is the affinity towards electron pairs.

Complete step by step answer:
- Ionization enthalpy
 On moving from left to right across a period, ionization enthalpy increases.
 With an increase in atomic number, the nuclear charge increases but the number of shells in the atoms of all the elements in a period remains the same. The nuclear attraction of the outermost electron increases because of which ionization enthalpy increases.

 - Atomic radius
 On moving from left to right across a period, the radii of atoms decreases.
There is an increase in nuclear charge of atoms as we move from left to right in the period due to electrons being added to the same shell and also rise in the number of protons in the nucleus. So, as atomic number increases, nuclear charge increases and therefore, atomic radius decreases along the period.

 - Electronegativity
The tendency to attract electrons is known as electronegativity.On moving from left to right across a period, electronegativity increases. As we move from left to right, electrons are added to the same valence shell. So, as more and more electrons are added, the probability of atoms attaining the octet or stable noble gas configuration increases. Like halogens need only one electron to achieve inert gas configuration and so, they have maximum tendency to accept electrons. Hence, the electronegativity increases from left to right in a period.
-The elements sodium to argon from period 3 of the periodic table also shows the same trend across moving left to right in period 3.
So, the correct answer is “Option C”.

Additional Information:
The third period contains eight elements. They are sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, and argon. The first two of the period 3 are sodium and magnesium, which are members of the s-block of the periodic table, while the others belong to the p-block. Na is alkali metal, Mg is alkaline earth metal, Al is a post-transitional metalloid, Si is metalloid, P, S, Cl are reactive nonmetal, and Ar is metalloid.

Note: In periodic table elements generally follow the basic trend but some exceptions regarding electron affinity, enthalpy, oxides, hydrides, electron-gain enthalpy are there. So if elements are mentioned then you should check according to it, not in basic trends.