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PHAtomic models explain how scientists understand the structure of the atom. Over time, these models improved as new experiments were performed. Here’s a clear, step-by-step overview:
1. Dalton’s Atomic Model (1803)
Scientist: John Dalton
Main Ideas:
Atom is a solid, indivisible sphere
All atoms of an element are identical
Atoms combine in fixed ratios
Limitation:
Could not explain subatomic particles (electron, proton, neutron)
2. Thomson’s Atomic Model (1897)
Scientist: J. J. Thomson
Main Ideas:
Atom is a positively charged sphere
Electrons are embedded like raisins in pudding
Limitation:
Failed to explain atomic nucleus
3. Rutherford’s Atomic Model (1911)
Scientist: Ernest Rutherford
Main Ideas:
Atom has a small dense nucleus
Electrons revolve around nucleus
Most of the atom is empty space
Experiment: Gold Foil Experiment
Limitation:
Could not explain why electrons don’t fall into nucleus
4. Bohr’s Atomic Model (1913)
Scientist: Niels Bohr
Main Ideas:
Electrons move in fixed orbits (energy levels)
Energy is quantized
Electrons jump between levels by absorbing/emitting energy
Limitation:
Works well only for hydrogen atom
5. Quantum Mechanical Model (Modern Model)
Scientists: Erwin Schrödinger, Werner Heisenberg
Main Ideas:
Electrons exist in probability clouds (orbitals)
Exact position cannot be known (uncertainty principle)
Uses mathematics and wave functions
Best Model:
Explains all atoms, bonding, and spectra
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