What is shelding effect and what are it's variation in periodic table?

Answer 1

In a group in the periodic table the shielding effect increases as we move from top to bottom. This is because of the increase in the number of shells as we move further down a group or family. When a new shell is added to an element, more electrons are added and the atomic size ( radius ) increases also. The more inner-shell electrons that come in between the nucleus and the valance (outermost) shell will cause the force of attraction between between the valance electrons to be less that those that are located closer to the nucleus. The shielding effect will increase.

However, when we move from left to right in a period in the periodic table, the shielding effect remains constant. This is because as we move from left to right in a period the number of valence electrons increases but no more shell are added. Since shielding effect is defined as the decrease in the force of attraction between the nucleus and the outermost (valence) shell due to the inner-shell electrons which orbit in between these two. When moving from left to right in a period more and more electrons are added in the same valence shell and the same number of electrons are in between the nucleus and the outermost shell.

We can understand this better with the help of examples. In Lithium, the atomic number is 3 and its electronic configuration is 1s2,2s1. In this example, there are 2 electrons between the nucleus and the outermost shell. Within the same period, for example, Magnesium, has an atomic number of 4 and its electronic configuration is 1s2,2s2. In magnesium, there are again only 2 electrons that are between the nucleus and the outermost electron. The other electrons are all being added to the outermost shell and since there are all in one shell the number of electrons between the nucleus and the outermost shell does not increase. For this reason, as we move from left to right in a period in the periodic table, the shielding effect remains constant or the same.

Answer 2

The shielding effect is the phenomenon where inner electron shells repel outer electrons, reducing the effective nuclear charge felt by the outer electrons. In general, the shielding effect increases as you move down a group in the Periodic Table due to the addition of more electron shells. The shielding effect tends to decrease across a period as the number of protons in the nucleus increases without a corresponding increase in shielding electrons.

Answer 3

The decrease in the attractive force exerted by the nucleus on the valence shall due to presence of the electron laying between the nucleus and valence shall is called shielding effect