Bohr's Model — Electron energy, radius (same as Physics)
Atomic Structure
9
JEE Qs
8%
Hard
60
min
Master the direct and inverse proportionalities with 'n' and 'Z' for radius, energy, and velocity to solve problems quickly without always calculating exact values.
🧮 Key Formulas
✅ Key Points for JEE
- 1Bohr's model is applicable ONLY for single-electron species (e.g., H, He^+, Li^2+, Be^3+).
- 2Electron energy (E_n) is quantized and negative, indicating a bound state. Energy increases (becomes less negative) as the principal quantum number (n) increases.
- 3The radius of the electron's orbit (r_n) is quantized. It increases quadratically with 'n' and is inversely proportional to the atomic number 'Z'.
- 4For a given orbit 'n', the Kinetic Energy (KE) is equal to the negative of the Total Energy (E_n), and the Potential Energy (PE) is twice the Total Energy (E_n).
⚠️ Common Mistakes
- ✕Applying Bohr's model to multi-electron systems (e.g., He atom, not He+ ion).
- ✕Incorrectly using the signs of energy components: Total Energy (E_n) is negative, Kinetic Energy (KE) is positive, Potential Energy (PE) is negative.
- ✕Using inconsistent units (e.g., mixing eV and Joules without proper conversion) or incorrect values for constants like the Rydberg constant.
📝 Practice Questions
See allQ57.Given below are two statements : Statement (I) : For a given shell, the total number of allowed orbitals is given by n2 . Statement (II) : For any subshell, the spatial orientation of the orbitals is given by −l to +l values including zero. In the light of the above statements, choose the correct answer from the options given below : (1) Both Statement I and Statement II are false (2) Statement I is true but Statement II is false (3) Both Statement I and Statement II are true (4) Statement I is false but Statement II is true
Q57.In a multielectron atom, which of the following orbitals described by three quantum numbers will have same energy in absence of electric and magnetic fields? A. n = 1, l = 0, m1 = 0 B. n = 2, l = 0, m1 = 0 C. n = 2, l = 1, m1 = 1 D. n = 3, l = 2, m1 = 1 E. n = 3, l = 2, m1 = 0 Choose the correct answer from the options given below: (1) B and C Only (2) A and B Only (3) C and D Only (4) D and E Only
Q51.Radius of the first excited state of Helium ion is given as : a0 → radius of first stationary state of hydrogen atom. (1) r = 4a0 (2) r = 2a0 (3) r = a02 (4) r = a04
Q62.Given below are two statements : Statement (I) : A spectral line will be observed for a 2px →2py transition. Statement (II) : 2Px and 2py are degenerate orbitals. In the light of the above statements, choose the correct answer from the options given below : (1) Both Statement I and Statement II are true (2) Statement I is false but Statement II is true (3) Both Statement I and Statement II are false (4) Statement I is true but Statement II is false
Q51.For hydrogen atom, the orbital/s with lowest energy is/are : (A) 4 s (B) 3px (C) 3 dx2−y2 (D) 3 dz2 (E) 4pz Choose the correct answer from the options given below : (1) (B), (C) and (D) only (2) (A) and (E) only (3) (A) only (4) (B) only
Q44.The frequency of revolution of the electron in Bohr's orbit varies with n, the principal quantum number as (1) 1 (2) 1 n4 n2 (3) 1 (4) 1 n n3
NCERT Chapters
- Class 11 Chemistry Ch 2: Structure of Atom
- Class 12 Physics Ch 12: Atoms