Atomic models

John Daltons solid sphere model

1. Matter is composed of tiny, indivisible particles called atoms.

2. All atoms of a given element are identical in mass and properties, while atoms of different elements vary.

3. Chemical reactions occur through the rearrangement and combination of atoms.

Pros: Introduced the concept of atoms as discrete units. > • Explained the fixed ratios in chemical compounds and the law of multiple proportions.

Cons: Could not explain the existence of subatomic particles (protons, electrons, neutrons). > • Viewed atoms as indivisible, a view later refuted by discoveries of internal structure.

J.J Thomsons plum pudding model

Atoms consist of a diffuse, positively charged "pudding" with negatively charged electrons embedded throughout much like plums in a pudding.

• First model to introduce subatomic particles (electrons).

• Emphasized the overall electrical neutrality of the atom.

• Pros: Introduced electrons into the atomic structure. > • Laid the foundation for further exploration of subatomic particles.

• Cons: Did not explain how the positive charge is arranged (no nucleus). > • Could not account for experimental results like the scattering of alpha particles.

Ernest Rutherford atomic model

An atom has a small, dense, and positively charged nucleus where most of the mass is concentrated, and electrons orbit this nucleus.

• Most of the atom’s volume is empty space.

• The intense deflections of some alpha particles showed the existence of a compact nucleus.

• Pros: Explained results of the gold foil experiment. > • Introduced the concept of a nuclear structure within atoms.

• Cons: Could not explain why electrons do not spiral into the nucleus (classical physics predicted energy loss during electron “orbit”) Failed to describe the atomic emission spectra.

Bohrs planetary model

• Electrons revolve around the nucleus in fixed, quantized orbits (energy levels).

• Electrons jump between orbits by absorbing or emitting precise amounts of energy.

• Successfully explained the discrete spectral lines of hydrogen.

• Introduced the idea of energy quantization in atomic systems.

• Pros: Accurately explained the hydrogen emission spectrum Introduced the concept of quantized energy levels.

• Cons: Applicable mainly to single-electron atoms (like hydrogen). > • Ignored electron–electron interactions and the wave nature of electrons.

Quantum Mechanical model

Concept: Electrons exist in orbitals—regions of probability—rather than in fixed orbits

Pros: > • Offers a highly accurate explanation of atomic and molecular behavior.Effectively describes multi-electron atoms and the complexity of chemical bonding.

Cons:The probabilistic nature and abstract mathematics can be challenging to visualize. > • Counterintuitive compared to earlier “planetary” models of the atom.