Why did Bohr’s model fail for multi-electron atoms?

Bohr’s model assumes electrons move in fixed circular orbits and considers only Coulombic attraction between nucleus and one electron. In multi-electron atoms, electron–electron repulsion, shielding, and relativistic effects alter energy levels, which the Bohr model cannot explain.

Why does the hydrogen atom show a line spectrum instead of a continuous spectrum?

Because electrons in hydrogen can occupy only quantized energy levels. When an electron transitions between these levels, it emits or absorbs photons of specific energies, producing discrete spectral lines.

Why is 4s filled before 3d in electronic configuration?

According to the (n + l) rule, orbitals with lower (n + l) value fill first. For 4s, n+l = 4; for 3d, n+l = 5. Hence 4s has lower energy initially and is filled before 3d.

Why are half-filled and fully filled subshells more stable?

Half-filled and fully filled subshells have symmetrical electron distribution and maximum exchange energy, which lowers overall energy and increases stability.

Why does effective nuclear charge increase across a period?

Across a period, proton number increases while shielding remains nearly constant because electrons are added to the same shell. Thus, net attractive force on valence electrons increases.

Why does atomic size decrease across a period?

Increasing effective nuclear charge pulls electrons closer to the nucleus without significant increase in shielding, reducing atomic radius.

Why does atomic radius increase down a group?

Down a group, additional electron shells are added, increasing distance between nucleus and valence electrons. Shielding effect also increases, enlarging atomic size.

Why is Heisenberg’s uncertainty principle important in atomic structure?

It establishes that position and momentum of an electron cannot be simultaneously determined with precision, proving that electrons cannot have fixed classical orbits.

Why are d-orbitals five in number?

For l = 2 (d-subshell), magnetic quantum number m? can take values -2, -1, 0, +1, +2. Thus there are five possible orientations, giving five d-orbitals.

Why does ionization energy generally increase across a period?

Increasing effective nuclear charge holds valence electrons more strongly, requiring more energy to remove an electron.

Why is the energy of electron in hydrogen negative?

Zero energy is defined when electron is infinitely far from nucleus. In bound state, electron possesses less energy than free state, hence energy is negative.

Why does the Balmer series appear in the visible region?

Balmer series corresponds to transitions ending at n = 2. The energy differences for these transitions fall within visible wavelength range.

Why does shielding effect reduce effective nuclear charge?

Inner shell electrons repel outer electrons, partially screening the nuclear attraction, thereby reducing the net effective nuclear charge experienced by valence electrons.

Why are orbitals described as probability clouds?

Quantum mechanics defines electron position in terms of probability density derived from wave function \(\psi\). The square of wave function \((\psi)^2\) gives probability distribution.

Why does Pauli exclusion principle limit two electrons per orbital?

Each orbital can have only one set of four quantum numbers. Since spin quantum number has only two values (+½ and -½), maximum two electrons can occupy one orbital with opposite spins.

Structure of Atom Class 11 NCERT true-false

Updated for 2026 Boards • JEE • NEET

Structure of Atom Class 11 – True/False Practice (NCERT Chapter 2)

Test your understanding of modern atomic theory with exam‑style True/False questions. Each statement targets core ideas like models of the atom, quantum numbers, and electronic configuration to sharpen accuracy for Boards, JEE, and NEET.

Last Updated: February 2026 | Practice Set – Instant Feedback

Interactive True/False quiz with instant checking, score tracking, and a downloadable PDF answer sheet containing all questions, correct answers, and brief explanations for your attempted statements.

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Reviewed by Subject Experts • Updated Feb 2026

Academia Aeternum Editorial Team

Reviewed by Subject Experts • Updated Feb 2026

Why Structure of Atom MCQs Matter for JEE & NEET

MCQs from this chapter frequently check ideas like quantum numbers, electronic configuration, and spectral lines in a time-bound format. Regular practice improves speed, accuracy, and your grip on conceptual traps.

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How Structure of Atom MCQs Appear in JEE & NEET 2026

Recent papers emphasise multi‑concept MCQs linking Bohr’s model, de Broglie relation, and quantum numbers in a single question. Many items are NCERT‑based but framed with tricky options and calculation‑heavy data.

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Most students lose marks in JEE & NEET not because they don’t know theory — but because they misread one word like “always” or “only”.

Structure of Atom Class 11 – True/False Practice (NCERT Chapter 2)

Why Structure of Atom MCQs Matter for JEE & NEET

How Structure of Atom MCQs Appear in JEE & NEET 2026

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