Question

Describe the quantum mechanical model of the atom. Why is this model more accurate than the classical model?

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Answer 1

The quantum mechanical model is based on the quantum mechanics. The quantum mechanics is a branch of science that takes into account dual behavior (particle and wave) of matter and quantum theory also defines the uncertainty principle.

According to this theory, atom assumes to be a system whose energy does not change with time.It defines a mathematical expression (Schrodinger equation) for a system. When this Schrodinger equation is solved, the solution gives the possible energy level the electron can occupy and corresponding wave function (atomic orbital) of the electron associated with each energy level. To characterize characteristic of the electron, energy level and wave function (atomic orbital) of an electron, quantum theory defines four quantum numbers.

Principle quantum number (n) – ‘n’ determines the size and the energy of the orbital and also identified the shell (K, L, M, N…). For n = 1 shell will be K

Azimuthal quantum number (l) – ‘l’ define the 3-dimensional shape of orbital and also define subshell (s, p, d, f…) l = n - 1. For l = 1, the subshell is 's'

Magnetic quantum number (m) – ‘m’ define the spatial orientation of the orbital with respect to standard set of coordinate axis and m = 2l + 1

Spin quantum number (ms) – angular momentum of the electron is a vector quantity therefore, it can have two orientation and this two orientation are distinguished by spin quantum number. ms = -1/2 or 1/2

Other terms-

Wavefunction (atomic orbital) is a mathematical function whose value depends on the coordinates of the electron in the atom and does not carry any physical meaning. Wavefunction contains all the information about the electron.

Atomic orbital - when we define wave function of hydrogen or hydrogen-like species with one electron, we will use atomic orbital instead of wave function

Uncertainty principle – it is impossible to know the exact position and momentum of an electron at the same time

=> According to classical model atom have fixed orbit and also have fixed position but according to quantum theory electron of an atom can find anywhere in their orbit and also we can find the probability of electrons in a space. According to the probability, the quantum theory defines the orbital shape of the electron.

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