In our previous blogs we talked about different structures of atom. When structure of atom was stablished as we discussed in our last
blog, scientists studied about arrangements of atoms in the orbitals and
atomic valency. Today we will discuss about distribution of electrons in
different orbitals.
Irving Langmuir was the first to propose the distribution of electrons in different orbitals. In 1919 he published an article "The Arrangement of Electrons in Atoms and Molecules" in which he explained the arrangements. In 1923 Niels Bohr incorporated Langmuir’s model that the periodicity in the properties of the elements might be explained by the electronic structure of the atom. His proposals were based on the current Bohr model of the atom. The following rules are suggested for writing the number of electrons in different energy levels or shells:
- The maximum number of electrons present in a shell is given by the formula 2n2, where ‘n’ is the orbit number or energy level index, 1,2,3,…. Hence the maximum number of electrons in different shells are as follows:
- first orbit or K-shell will be = 2 × 12 = 2,
- second orbit or L-shell will be = 2 × 22 = 8,
- third orbit or M-shell will be = 2 × 32 = 18,
- fourth orbit or N-shell will be = 2 × 42 = 32, and so on.
- The maximum number of electrons that can be accommodated in the outermost orbit is 8.
- Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner.
However electronic configuration was first conceived under the Bohr model of the atom, and it is still common to speak of shells and subshells. But advanced concepts clarifications are based on the understanding of the quantum-mechanical nature of electrons. Hence we will talk about these concepts in our later and advanced episodes. Until then these are enough to know.
Fore more details refer to Beyond Reaction: Fundamental Chemistry
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