Bohr's Model Radius Calculation NEET Cheat Sheet: Everything You Need
Bohr's ModelStructure of AtomNEET ChemistryNEET 2025Atomic RadiusQuantum NumbersBohr Radius Calculation
Bohr's Model Radius Calculation NEET Cheat Sheet: Everything You Need
Structure of Atom·2 min read·NEET 2026
What NEET Asks
Direct application of Bohr's radius formula for hydrogen and hydrogen-like species.
Questions on proportionality of radius with principal quantum number (n) and atomic number (Z).
Comparative analysis of radii for different orbits or species. Expected 1-2 questions, generally easy to medium, testing either direct formula application or comparative analysis.
Key Points
Bohr's model applies only to single-electron species (H, He$^+$, Li$^{2+}$, Be$^{3+}$).
The electron revolves in fixed circular orbits called stationary states, without radiating energy.
$n$: Principal quantum number (integer representing the orbit number)
$Z$: Atomic number of the hydrogen-like species
Common Mistakes
Students often forget to square 'n' in the formula. Remember it's $n^2$, not just $n$.
Don't confuse 'Z' (atomic number) with the number of electrons. The formula uses Z for the nuclear charge.
Incorrectly applying the formula to multi-electron species or atoms; it's strictly for H-like species only.
Rapid Revision
Bohr's radius for H-like species: $r_n = 0.529 \times (n^2/Z)$ Å. Remember the proportionality $r_n \propto n^2/Z$. Quickly recall this proportionality and the constant for direct problem solving and ratio-based questions.
Frequently Asked Questions
What is the significance of the Bohr radius in chemistry?▾
The Bohr radius ($a_0$ or $r_1$ for hydrogen) represents the most probable distance between the proton and electron in a hydrogen atom in its ground state. It's a fundamental constant used as a unit of length in atomic physics and a reference for other atomic radii.
How does the radius of an orbit change with increasing principal quantum number (n) and atomic number (Z)?▾
The radius of an orbit ($r_n$) is directly proportional to the square of the principal quantum number ($n^2$) and inversely proportional to the atomic number ($Z$). So, as 'n' increases, $r_n$ increases rapidly, and as 'Z' increases, $r_n$ decreases, making the orbit smaller and closer to the nucleus.
Can Bohr's model be used to calculate the radius of orbits for multi-electron atoms?▾
No, Bohr's model is strictly applicable only to single-electron species, also known as hydrogen-like species, such as H, He$^+$, Li$^{2+}$, and Be$^{3+}$. It fails to accurately explain the spectra and properties of multi-electron atoms due to electron-electron repulsions.
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