Structure of Atom
Class 11 · Chemistry
4 ideas in Class 11 Chemistry, explained in plain words, with games and quizzes to practise.
Discovering Subatomic Particles
Part of: Particles, Light and Spectra
Cathode rays revealed negative electrons; oil drops weighed their charge. Canal rays added positive protons, and beryllium bombardment freed neutral neutrons. Gold-foil rebounds crushed the pudding model, leaving a tiny nucleus with circling electrons.
Why it matters. Each beam experiment rewrote the atom. Knowing who found what stops the models blurring together.
Formulas
- Atomic number = proton count; mass number = protons + neutrons.
Key words
- Electron
- : The negative particle found in cathode rays.
- Proton
- : The positive particle from canal rays.
- Neutron
- : The neutral particle freed by beryllium bombardment.
- Nucleus
- : The tiny dense core holding the mass.
- Isotopes
- : Same protons with different neutrons, as in protium and deuterium.
- Isobars
- : Same mass number with different atomic numbers.
Try it in two minutes
- Bend an imaginary beam with a magnet.
- Scatter marbles at a hidden core.
- Sort hydrogen's three isotopes by neutrons.
Try at home. Compare plum pudding with nuclear sketches.
Light, Spectra and the Quantum
Part of: Particles, Light and Spectra
Light's speed ties frequency to wavelength. Energy arrives in photon packets sized by frequency, knocking out electrons only above the work function. Heated gases emit sharp lines; hydrogen's series follow Rydberg's formula by level jumps.
Why it matters. Flame colours, lasers and starlight all speak lines. Photons explain why colour beats brightness.
Formulas
- c = frequency x wavelength
- E = h x frequency
- Wavenumber = R (1/n1^2 - 1/n2^2)
Key words
- Photon
- : One energy packet of light, sized by frequency.
- Work function
- : The minimum energy to knock out an electron.
- Line spectrum
- : Sharp bright lines, a fingerprint of each element.
- Rydberg formula
- : Level jumps fixing hydrogen line positions.
Try it in two minutes
- Split sunlight with a spray prism.
- Compare red and blue photon energies.
- Match flame colours with metals.
Try at home. View street lamps through a CD rainbow.
Bohr Model and Electron Waves
Part of: Models, Waves and Configurations
Bohr locks electrons to shells with energies falling as one over n squared and radii growing as n squared. Matter also waves: wavelength is Planck's constant over momentum, and position with momentum share a minimum blur.
Why it matters. Shell energies decode every line spectrum. Duality ends exact orbits and starts orbitals.
Formulas
- En = - 2.18 x 10^-18 / n^2 joules (hydrogen)
- Radius grows as n^2: r2 = 4 x r1
- Wavelength = h / (m v)
Key words
- Bohr orbit
- : A shell with energy falling as one over n squared.
- Ground state
- : The lowest shell, minus 2.18 times 10 to the power minus 18 joules for hydrogen.
- de Broglie wavelength
- : Planck constant over momentum.
- Uncertainty principle
- : Position with momentum share a minimum blur.
Try it in two minutes
- Fit whole waves around a ring.
- Drop an electron between shells and count the photon.
- Blur a spot to sharpen its speed.
Try at home. Compare hydrogen red with mercury violet lines.
Orbitals and Electronic Configuration
Part of: Models, Waves and Configurations
Four quantum numbers address each electron: shell, shape, orientation and spin. Lower n-plus-l fills first; one electron per orbital precedes pairing with parallel spins; no pair shares an address. Half and full shells borrow stability, flipping chromium and copper.
Why it matters. Addresses predict the whole periodic table. Exceptions test whether rules are truly understood.
Formulas
- Fill order follows lower (n + l); ties break to lower n.
- Orbitals per shell = n^2; electrons per shell = 2 n^2.
Key words
- Orbital
- : A region shaped by shell, shape, orientation and spin numbers.
- Aufbau order
- : Lower n-plus-l fills first.
- Hund's rule
- : One electron per orbital precedes pairing, with parallel spins.
- Pauli principle
- : No pair shares all four quantum numbers.
- Half-filled stability
- : Extra stability flipping chromium and copper.
Try it in two minutes
- Fill 1s, 2s, 2p for the first ten elements.
- Spread three p electrons singly first.
- Spot the chromium and copper flips.
Try at home. Write configurations up to calcium from memory.
What your child will practise
- Bohr Model and Electron Waves: Jungle Puzzle (Clue Puzzle)
- Bohr Model and Electron Waves: Jungle Quick Fire (Quick Fire)
- Discovering Subatomic Particles: Candy Puzzle (Clue Puzzle)
- Light, Spectra and the Quantum: Desert Quick Fire (Quick Fire)
- Orbitals and Electronic Configuration: Candy Quest (Flip and Match)
- Quiz: Bohr Model and Electron Waves (8 questions)
- Quiz: Discovering Subatomic Particles (8 questions)
- Quiz: Light, Spectra and the Quantum (8 questions)
- Quiz: Orbitals and Electronic Configuration (8 questions)