# Structure of Atom Notes, Class 11 Chemistry | SwaVid Structure of Atom, NCERT Class 11 Chemistry: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers. Canonical: https://www.swavid.com/cbse/class-11/chemistry/chapter/structure-of-atom Source: https://www.swavid.com/cbse/class-11/chemistry/chapter/structure-of-atom # Structure of Atom ## Formulas and definitions ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 11 Chemistry on SwaVid ### Subatomic particles and atomic models ### Dual nature of electromagnetic radiation ### Bohr model of hydrogen ### Dual nature of matter and uncertainty ### Quantum mechanical model ### Quantum numbers and orbitals ### Rules for electronic configuration ### Next chapter ### Related chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 11 › Chemistry › Structure of Atom Notes written by SwaVid from the NCERT textbook. Class 11 Chemistry, Unit 2. Key ideas, formulas and common mistakes. CBSE prints 9 marks for Unit 2, not for this chapter alone. Short answer. This chapter traces the development of atomic models from early subatomic discoveries to quantum mechanics. Students learn to describe electrons using wave-particle duality, uncertainty, and four quantum numbers that govern electronic configurations. Source: NCERT Chemistry Part I (Reprint 2026-27) , Unit 2, Structure of Atom Atoms contain electrons, protons, and neutrons. Rutherford's nuclear model showed a dense positive nucleus with electrons around it, but it could not explain atomic stability or discrete line spectra. Light behaves both as waves and as particles called photons. Planck's quantum theory and the photoelectric effect established that energy is emitted or absorbed in discrete packets called quanta. Bohr proposed that electrons move in fixed circular orbits with quantized angular momentum. Electrons emit or absorb energy only when jumping between orbits, producing discrete spectral lines. De Broglie proposed that microscopic particles like electrons have wave properties. Heisenberg's uncertainty principle showed that the exact position and momentum of an electron cannot be measured simultaneously. The Schrödinger equation treats electrons as three-dimensional waves, replacing defined orbits with probability regions called orbitals. The square of the wave function, |ψ|², gives the probability density of finding an electron. Four quantum numbers (n, l, mₗ, mₛ) define the size, shape, spatial orientation, and spin of an electron in an atom. Orbitals of the same subshell have the same energy and are called degenerate orbitals. Electrons fill orbitals according to the Aufbau principle, the Pauli exclusion principle, and Hund's rule of maximum multiplicity. Half-filled and fully-filled subshells possess extra stability due to symmetry and exchange energy. Try each question first. Then tap it to see the answer. E = hν E = 6.626 × 10⁻³⁴ J s × 3.0 × 10¹⁵ s⁻¹ E = 1.988 × 10⁻¹⁸ J 1.99 × 10⁻¹⁸ J λ = h / (m × v) λ = 6.626 × 10⁻³⁴ / (9.11 × 10⁻³¹ × 2.05 × 10⁷) λ = 6.626 × 10⁻³⁴ / 1.868 × 10⁻²³ λ = 3.55 × 10⁻¹¹ m 3.55 × 10⁻¹¹ m The principal quantum number n = 4 and azimuthal quantum number l = 2 correspond to the d subshell, giving 4d. The number of orbitals in a subshell is given by 2l + 1. Number of orbitals = 2(2) + 1 = 5, corresponding to mₗ = -2, -1, 0, +1, +2. 4d subshell, 5 orbitals Classification of Elements and Periodicity in Properties . Some Basic Concepts of Chemistry . Chemical Bonding and Molecular Structure . The 9 chapters of Class 11 Chemistry . CBSE does not give marks to one chapter. It prints 9 marks for Unit 2, Structure of Atom, which includes Structure of Atom. No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed. Classification of Elements and Periodicity in Properties. SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works. - Unit 2 NCERT book - 9 marks, Unit 2 - 3 quick checks - Treating orbits and orbitals as the same concept . An orbit is a fixed, well-defined circular planar path from the Bohr model. An orbital is a three-dimensional region of space where the probability of finding an electron is high. - Using the Bohr energy formula for multi-electron atoms . Bohr's formulas apply only to hydrogen and hydrogen-like single-electron species such as He⁺, Li²⁺, and Be³⁺. - Ignoring the (n + l) rule and writing 3d before 4s in filling order . For 4s, n + l = 4 + 0 = 4. For 3d, n + l = 3 + 2 = 5. Therefore, 4s has lower energy and fills before 3d. - Writing regular configurations for chromium and copper . Chromium is [Ar] 3d⁵ 4s¹ and copper is [Ar] 3d¹⁰ 4s¹, because half-filled (d⁵) and completely filled (d¹⁰) subshells have extra stability. ## Key Links - [CBSE](https://www.swavid.com/cbse) - [Class 11](https://www.swavid.com/cbse/class-11) - [Chemistry](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [Start free →](https://www.swavid.com/signup) - [All 9 chapters](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [NCERT Chemistry Part I (Reprint 2026-27)](https://ncert.nic.in/textbook.php) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/classification-of-elements-and-periodicity-in-properties) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/some-basic-concepts-of-chemistry) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/chemical-bonding-and-molecular-structure) - [Class 11 Chemistry](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [Start free →](https://www.swavid.com/signup)