Energy Levels in Atom - NEET Notes, Formula & Common Mistakes
Energy LevelsStructure of AtomNEET ChemistryNEET 2025Bohr ModelAtomic SpectraQuantum Numbers
Energy Levels in Atom - NEET Notes, Formula & Common Mistakes
Structure of Atom·2 min read·NEET 2026
What NEET Asks
Direct calculation based on Bohr's energy formula for H-like species.
Conceptual questions on ground state, excited states, and ionization energy.
Problems involving electron transitions, emission/absorption spectra, and calculating energy/wavelength.
Key Points
Quantized Energy: Electrons occupy specific, discrete energy levels (shells) around the nucleus, denoted by principal quantum number n (1, 2, 3...). Each level has a fixed energy.
Ground State: The lowest energy state (n=1) where the electron is most stable. This is the natural, unexcited state.
: Any energy state higher than the ground state (n > 1). Electrons reach here by absorbing energy.
Excited State
Energy Relation: Energy levels become closer as n increases. The energy $E_n \propto -1/n^2$ for H-like species. Higher 'n' means less negative (higher) energy.
Electron Transitions: Electrons absorb energy to move to higher n (excitation) and emit energy (as photons) when moving to lower n (de-excitation), forming atomic spectra.
Ionization Energy: Energy required to remove an electron completely from an atom (from n=1 to n=∞).
Must-Know Formula / Reaction
$E_n = -13.6 \frac{Z^2}{n^2}$ eV/atom
$E_n$: Energy of electron in the $n^{th}$ orbit.
Z: Atomic number of the H-like species (e.g., H, He⁺, Li²⁺).
n: Principal quantum number (orbit number, e.g., 1 for ground state, 2 for first excited state).
Common Mistakes
Students often forget to square the atomic number (Z) when dealing with H-like species other than hydrogen.
Don't confuse emission (energy released, electron moves to lower n) with absorption (energy absorbed, electron moves to higher n). The sign of ΔE is crucial.
Incorrectly applying the relationship between energy, frequency, and wavelength (e.g., longest wavelength corresponds to smallest energy difference).
Rapid Revision
Atomic energy levels are quantized, described by 'n'. The ground state (n=1) is lowest energy. Energy increases with 'n'. Electron transitions cause emission or absorption spectra. Remember $E_n = -13.6 \frac{Z^2}{n^2}$ eV for H-like atoms. Ionization means n=1 to n=∞.
Frequently Asked Questions
What are energy levels in an atom according to Bohr's model?▾
According to Bohr's model, electrons in an atom revolve around the nucleus in specific, discrete circular paths called orbits or shells. Each orbit is associated with a fixed amount of energy, hence they are called energy levels or stationary states.
How is the energy of an electron related to its principal quantum number 'n'?▾
The energy of an electron in a given orbit is inversely proportional to the square of its principal quantum number 'n' ($E_n \propto -1/n^2$). As 'n' increases, the electron's energy becomes less negative, meaning it increases.
Why are the energy values for electrons in an atom negative?▾
The negative sign for energy values indicates that the electron is bound to the nucleus and requires energy to be removed. By convention, the energy of a free electron (infinitely far from the nucleus) is taken as zero. Since energy is released when an electron falls into an orbit, its energy in an orbit is considered negative relative to a free electron.
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