Question

Compare the following elements as per the characteristic given in the brackets. Give the reason for your answer in each case.
A.Lithium and Nitrogen (Atomic radii)
B.Potassium and Chlorine (Electronegativity)
C.Magnesium and Calcium (Valency)

Answer 1

To answer this question, you should recall the trends in the periodic table. Atomic radii increases down the group and decreases across the period. Electronegativity increases across the period. Valency increases for metals and decreases for non metals across the period.

Complete step by step answer:
A.The atomic radius of atoms generally decreases from left to right across a period. They increase on moving from top to bottom in a group as the number of shells increases with the increase in atomic number. Hence, Lithium has a larger atomic radius than nitrogen because nitrogen has higher forces of interaction within its atom.
B.The electronegativity of atoms increases as you move from left to right across a period in the periodic table. The reason is that the nuclear charge is increasing faster than the electron shielding, so the attraction that the atoms have for the valence electrons increases. Atoms with high ionization energies have high electronegativities because the nucleus has a strong attraction for electrons. Hence, the electronegativity of chlorine is higher than potassium.
C.While moving left to right across a period, the number of valence electrons of elements increases and varies. As we move down in a group the number of valence electrons does not change. Valency of both magnesium and calcium is the same which is $+ 2$. It is due to ${\text{Mg}}$ and ${\text{Ca}}$ both belong to group 2 of the periodic table.

Note:
Let us summarize the trends of fundamental properties of an element:
Atomic Radii and Ionic radii: The atomic radii and ionic radii of elements decrease while moving from left to right in a period.
Ionization Enthalpy: Across a period in the periodic table, ionization energy generally increases. For the trend in a group, ionization enthalpy decreases from top to bottom.
Electron gain enthalpy: Electron gain enthalpy becomes more negative as we move from left to right in a period. Electron gain enthalpy is negative when energy is released while accepting an electron. While it is positive when energy is supplied to an atom while adding an electron.