Chemistry · Structure Of Atom · NEET
Five points from NCERT: (1) The energy of electrons is quantized (only certain fixed values allowed). (2) We cannot know the exact path of the electron because of the Heisenberg uncertainty principle. (3) An orbital is the wave function psi for one electron, described by three quantum numbers n, l and m_l. (4) psi by itself has no physical meaning; |psi|^2 gives the probability density (chance of finding the electron per unit volume). (5) The model correctly explains the hydrogen spectrum, even parts the Bohr model could not.
An orbit is Bohr's idea: a fixed circular path where the electron moves. It cannot be true because the uncertainty principle says you cannot know both exact position and speed, so a fixed path is impossible. An orbital is different: it is a quantum mechanical wave function psi for one electron. It does not give a path; it gives a region of space where the electron is likely to be found. Short line: orbit = fixed path, orbital = probability region.
psi (the wave function) by ITSELF has NO physical meaning. It is just a mathematical function of the electron's coordinates. It is |psi|^2 (psi squared) that has meaning: it is the probability density, the chance of finding the electron in a tiny volume at that point. NEET loves this exact distinction, so remember: psi = no meaning, |psi|^2 = probability density.
Because of the Heisenberg uncertainty principle. To draw a fixed path you must know the electron's exact position AND its exact momentum (speed and direction) at the same time. The uncertainty principle says this is impossible for a tiny particle like an electron. So Bohr's fixed orbits have no real meaning, and we can only talk about the probability of where the electron is.
Quantized means the electron can only have certain allowed energy values, not any value in between. Think of stairs, not a ramp: you can stand on step 1 or step 2, but never halfway between. When the electron is bound to the nucleus in an atom, its energy is quantized into these fixed levels.
An orbital is described by THREE quantum numbers: n (principal), l (azimuthal) and m_l (magnetic). An electron in an atom needs FOUR quantum numbers because it also needs the spin quantum number m_s. This is a common NEET one-liner, so keep it separate: orbital = 3 numbers, electron = 4 numbers.
Statement I: The value of the wave function psi depends upon the coordinates of the electron in the atom. Statement II: The probability of finding an electron at a point within an atom is proportional to the orbital wave function psi. Choose the correct answer.
Which one is a wrong statement? (about orbitals and quantum numbers)
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It comes from Erwin Schrodinger's wave equation (1926) applied to atoms, built on de Broglie's dual nature of matter and Heisenberg's uncertainty principle.
It gives exact solutions only for the hydrogen atom and hydrogen-like one-electron species. For multi-electron atoms it uses approximate methods, but the same features (orbitals, quantum numbers, probability) still apply.
An atomic orbital is the one-electron wave function psi in an atom, characterized by three quantum numbers n, l and m_l. |psi|^2 tells you where the electron is likely to be.
It removes the false idea of fixed circular orbits (which break the uncertainty principle) and correctly predicts the full hydrogen spectrum, including details the Bohr model could not explain.
