What is screening effect? how does it relates with effective nuclear charge?
Answers
In the centre of any atom there is a positive charge which bind all the electrons around the atom. Sometimes, the atom is so large that a small proton which is concentrated in the nucleus, is unable to bind the outermost electrons because the inner electrons screens the outer electrons, due to which outermost electrons can easily comes out from the atom and the effect of screening of inner electrons to outer is called screening effect.
The effective nuclear charge is the net positive charge experienced by valence electrons.
Answer:
(i) Screening effect : The inner shell electrons in an atom screen or shield the outermost valence electrons from the nuclear attraction. This effect is called screening effect or shielding effect. The magnitude of screening effect depends upon the number of inner electrons. Higher the number of inner electrons, greater is the value of screening effect. The screening constant is represented by 'o' (sigma). For example, across a period the electrons enter the same shell. Thus, shielding due to inner electrons remain same. Down a group, a new larger valence shell is added which increases the inner electrons and thus the shielding effect increases
(ii) Effective nuclear charge : Due to screening effect the valency electrons experience less attraction towards nucleus. This reduces the active nuclear charge (z) actually present on the nucleus. This reduced nuclear charge is termed as 'effective nuclear charge. (Z_eff).