Question

Electrons which have highest penetrating power through lower orbitals is
A. p-electrons
B. s-electrons
C. d- electrons
D. f-electrons

Answer 1

Penetration describes the proximity to which an electron can approach to the nucleus. In a multi-electron system electron penetration is defined by its electron density (probability density ) near the nucleus of the atom.

Complete answer:
In an atom, electrons are negatively charged particles therefore repel each other, but due to the concentrated positive charge of the nucleus they are bound to revolve around the nucleus. The electrons repel each other but at the same time electrons are attracted to the nucleus. The orbital (n) and subshell (ml) defines how an electron can approach the nucleus. And this ability of electrons to approach the nucleus is penetration.
According to coulomb's law, the force an electron will feel depends upon the distance and charge. More distance between the charge leads to less force. And more charge will have more attraction. The simplest case can be that all electrons feel the same force from the nucleus. But this is not that easy when we have atomic behavior. The amount of charge felt by the electron will depend on the distance from the nucleus. That means the closer an electron comes to the nucleus, or the more it will penetrate, the stronger the attractive force between the two. The electrons that are closest to the nucleus penetrate more and will feel more of the nucleus than the other outer electrons.
The orbital penetration, in a multi-electron system, is defined as electron density near the nucleus. The penetration here depends upon the shell (n) and subshell (ml). Within the same shell generally S-electrons have more density near the nucleus of the atom than p, d, and f – electrons.

**Hence the correct option will be B. s-electrons

Note:**
The balance between the attractive force between electrons and nucleus and repulsive force between the electrons in an atom is defined as a shielding effect. The penetration and shielding effect determine the physical and chemical properties of elements.