Nuclear charge increases both in a period and group. But, the effective nuclear charge increases in a period and decreases in a group. Identify the correct reverse trend.
(A) Reverse trend of atomic size
(B) Role of screening effect
(C) Reverse trend of metallic character
(D) Role of inter electronic repulsions.
VerifiedHint: Nuclear charge is the total charge possessed by the nucleus of an atom, it is mostly the charge on the proton as neutrons are neutral. But the effective nuclear charge is the amount of nuclear charge experienced by the outermost electrons, it is often represented by ${\text{Z*}}$.
Complete answer:
Nuclear charge is a function of the number of protons present in an atom. And if we move from left to right or from top to bottom in a periodic table we can always observe an increase in Atomic number as there is an increase in the number of protons.
But the effective nuclear charge observes a decrease as we move down the group, and sees an increase as we move along the period.
Because, as we move down the group the electrons are added to a new orbital which increases the atomic size of the atom, and reduces the influence of the nucleus on the outermost electron, hence we observe a decreased value of the effective nuclear charge.
But as we go along the period, the number of protons increases, and the new electrons are added to the same orbital, which retains the nuclear charge of the atom, and the effective nuclear charge increases. As a result of the increased nuclear charge the size of the atom decreases.
Therefore, we can conclude that the reversed phenomenon responsible for the change of the trend is the atomic radius.
Hence, the correct answer is option (A).
Note: There could be a chance of confusion in the meaning of both the terms, nuclear charge, and effective nuclear charge both are quite similar but there is a slight difference, and this difference is rather significant and responsible for many governing factors for an atom, for eg: electron affinity, size, ionization potential, etc
