Structure of Atom — Class 11 Maharashtra HSC Chemistry revision notes
A 5-page visual revision sheet for Structure of Atom, written for Class 11 Maharashtra HSC Chemistry. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Structure of Atom in one look
one nucleus, a set of shells, and rules for who lives where
Three subatomic particles
- Electron: e^-, J.J. Thomson, 1897, cathode-ray tube. charge -1, mass ≈1/1837 of a proton's
- Proton: Rutherford, 1911-1919, alpha scattering and nitrogen transmutation. charge +1, mass ≈1 u
- Neutron: Chadwick, 1932, paraffin bombarded by beryllium radiation. no charge, mass ≈1 u, a shade above a proton's
Rutherford's alpha-scattering experiment
- a beam of α particles fired at a thin gold foil, only a few atoms thick
- most passed straight through undeflected: the atom is mostly empty space
- a small fraction deflected through large angles, about 1 in 20,000 bounced almost straight back
- that rebound meant a tiny, dense, positively charged core: the nucleus
- 1919: fast α particles turned nitrogen into oxygen, always releasing hydrogen, later renamed the proton
Rutherford's nuclear model, and where it broke
- mass and positive charge sit in a tiny nucleus (~10^-15 m), electrons revolve outside (~10^-10 m)
- modelled electrons like planets orbiting the nucleus under electrostatic attraction
- problem 1: an orbiting charge must radiate energy, so it should spiral in instantly, yet atoms don't
- problem 2: says nothing about why an electron sits at a given distance or hydrogen's line spectrum
Atomic number, mass number, notation
- atomic number, fixes the element
Z=p=e (in a neutral atom) - mass number, protons + neutrons
A=Z+N - standard notation for a nuclide
^A_ZX
Isotopes, isobars and isotones
- isotopes: same Z, different A, identical chemical behaviour, e.g. ^35_17Cl and ^37_17Cl
- isobars: same A, different Z, different elements, different chemical properties, e.g. ^40_18Ar and ^40_20Ca
- isotones: same neutron number N, different Z and A, e.g. ^11_5B and ^12_6C, both N=6
- don't confuse: iso-**TOPES** share a spot, iso-**BARS** a weight, iso-**TONES** a neutron count
Page 1 of 5. The full sheet, all 5 pages, opens free in the app.
What this Structure of Atom sheet covers
- Three subatomic particles
- Electron
- Proton
- Neutron
- Rutherford's alpha-scattering experiment
- Rutherford's nuclear model, and where it broke
- Atomic number, mass number, notation
- atomic number, fixes the element
- mass number, protons + neutrons
- standard notation for a nuclide
- Isotopes, isobars and isotones
- Worked: average atomic mass from isotope abundance
- Bohr's postulates
- Bohr model results, for H and hydrogen-like ions
- radius of the nth orbit
- energy of the nth orbit
- any transition: Rydberg formula
- Hydrogen's spectral series
- Lyman
- Balmer
- Paschen
- Brackett / Pfund
- Worked: wavelength of a Balmer transition
- Limitations of Bohr's model
- Dual nature of matter: de Broglie
- wavelength associated with a moving particle
- Heisenberg's uncertainty principle
- position and momentum can't both be known exactly
- Quantum mechanical model, in brief
- The four quantum numbers
- n: principal
- l: azimuthal
- ml: magnetic
- ms: spin
- Shells, subshells and orbital counts
- Shapes of s, p, d orbitals
- s orbital
- p orbital
- d orbital
- Aufbau principle: the (n+l) rule
- Pauli exclusion & Hund's rule
- Electronic configuration: the exceptions
- Isoelectronic species
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Chemistry chapter by chapter against your real exam dates and free hours, and when the plan reaches Structure of Atom the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.
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- Chemical Bonding
- Chemical Equilibrium
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- Elements of Group 1 and 2
- Elements of Group 13, 14 and 15
- Hydrocarbons
- Introduction to Analytical Chemistry
- Modern Periodic Table
- Nuclear Chemistry and Radioactivity
- Redox Reactions
- Some Analytical Techniques
- Some Basic Concepts of Chemistry
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