Question

What is an energy gap?
A. the space between two orbital shells
B. the energy equal to the energy acquired by an electron passing a 1 volt electric field.
C. the energy band in which electrons can move freely
D. an energy level at which an electron can exist

Answer 1

The electrons travel around the nucleus in fixed circular paths having discrete energy. These paths are known as stationary orbits. Each stationary orbit is associated with a particular energy and hence these are known as energy shells. The region between the shells is not accessible for an electron.

Complete step by step answer :
From the Bohr model of atoms, we know that the electrons travel around the nucleus only in fixed circular paths which are known as orbits.

There are only certain orbits in which the electron will be stable. Such orbits are called stationary orbits. Hence electrons can be seen around the nucleus only in these stationary orbits. Each stationary orbit has a discrete energy associated with it. Hence these orbits are called energy shells or energy levels. If we supply energy to the electron it can jump from lower energy level to higher energy level. Similarly, when an electron loses energy it falls from higher energy level to lower energy level. An electron cannot occupy space between these energy levels. Electrons will orbit around the nucleus stably without radiating energy only in the stationary orbit.

So, the space between the stationary orbit is not accessible for an electron. And this region is known as the energy gap. On receiving energy electrons can cross this energy gap and go to higher levels. And by losing energy electrons can come back to the lower level. But it cannot stay in the region between the energy shells.

So, the energy gap is the region between two orbital shells.

Hence the correct answer is option A.

Note: If an electron is in an Orbit other than stationary orbit, then it will radiate energy in the form of electromagnetic waves. But in the case of stationary orbit this does not happen because of the formation of a standing wave. So, the electron can occupy only a discrete set of energy levels.