![]() ![]() Now then you want to come down to the ground floor you may plenty of options. Suppose, in an apartment you have traveled from ground floor to fifth floor by using lift. In order to understand the process very easily let’s take an illustration. Every electronic state is associated with several vibrational states and every vibrational state is associated with several rotational states. Now electrons in a molecule may have three in states at any moment.Īccordingly it will have corresponding energies associated with each state. Electrons can also have rotational transitions which are not that much significant in molecular absorption and emission. Of course, the majority of the absorbed energy is utilized for electronic transitions and then for vibrational transitions. So when a light falls on a molecule, the energy is utilized for both electronic and vibrational transitions. Every chemical bond is like a spring that always produces some vibrations between the atoms in molecule. The situation is not so simple, as molecules are made up of atoms with variety of linkages such as sigma bond and pi bond. Now let’s turn our discussion on molecules. In this way, atomic spectra always produce line spectra at definite wavelengths. So whatever the energy required for an electron to jump from third orbit to fourth orbit is fixed and equal to the energy released by electron jumping back from fourth orbit to third orbit. By this way, the energy gap between any two orbitals is fixed. So if an electron is third orbit, it will have a definite energy while fourth orbit another specified energy. One of the interesting facts with atoms is that the energy associated with each orbit is fixed. Similarly, it can come back to original orbital by releasing the energy. Now when we supply energy, the electron in the outer orbital can jump to the next orbital by absorbing the energy. Here outer electrons are present in fourth orbit within s orbital. Similarly if we consider potassium, it has atomic number 19 and electronic configuration is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1. So its outer electrons are present in third orbit within s orbital. ![]() That means, their electrons are distributed in fixed orbitals in each orbit.įor example, sodium has atomic number as 11 and its electronic configuration is 1s 2 2s 2 2p 6 3s 1. We know that atoms have definite atomic number and corresponding electronic configuration. Here we will see why molecules differ from atoms in spectroscopy. Molecules show brand spectra and they absorb or emit not a specific wavelength but at a range of wavelengths. But in case of molecules the situation is different. In another words, it has similar absorption and emission spectra both involve a single wavelength resulting in line spectra. Sodium metal absorbs radiation at 589 nm and emits again at the same wavelength. ![]()
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