Question

Atomic and molecular spectra are discrete. What does discrete mean, and how are discrete spectra related to the quantization of energy and electron orbits in atoms and molecules?

Answer 1

Solution : any quantity or value which can obtain only some specific values or some exact values is called discrete. The quantity can be found only in integral multiple of a predefined unit. For example I give you simple situation when you are moving up on a staircase you can be on either 2nd or 3rd stair but you can't be on 2.5th stair. Which means that the data can have only values 1,2,3,4 and so on. It can't be 2.3,2.5 etc.

Then we use the term that the data is discrete .

Every atom and molecule is composed of nucleas and electrons . The electrons are revoluting in some specific predefined path called orbits. Every orbit has its own energy and fixed distance from the nucleas.

If you have read bohr model you would be knowing about it already. As the election can be found only in orbits therefore they can have some certain value of energy . Any electron transferring from one orbit to another would require energy equal to the difference of the energy of orbits. Hence the electron can take only some certain and fix value of energy hence atom gives discrete spectra.

Suppose electron is orbiting in first orbit having an energy of 13.6ev then it jumps to 4th orbit having energy 2.4 ev then electrom during this transmission will emit 11.2 eV energy. As every orbit is fixed hence the energy difference is fixed so some certain values only can be obtained . So the spectrum is called discrete spectrum.