Science teachers often rely on analogies and comparisons to help students picture what an atom “looks like”. The following activities aim to help students understand the atom, as it serves as the foundation for the rest of chemistry and plays an important role in many parts of physics.
Democritus used the word atomos, Greek for unbreakable, to describe the smallest parts of matter. His is an early atomic theory, though he lacked evidence.
THOMSON
DALTON
The cathode ray experiment helped Thomson realize that the atom could be divided into smaller parts, including a negatively charged part called the electron.
Five Statements of Atomic Theory, with evidence
He theorized that the positive part of the atom was like pudding with electrons embedded in it.
All elements are made of atoms that differ from one another. Atoms of the same element are identical. Atoms combine in whole number ratios.
RUTHERFORD
With the gold foil experiment, Rutherford discovered the small, dense center of the atom and named it the nucleus.
BOHR
By studying the spectral lines of hydrogen, Bohr theorized that electrons move at fixed energies, in paths he called orbits. His model described H perfectly.
ELECTRON CLOUD MODEL
The modern idea of the atom suggests the probability of "locating" an electron in mathematically-determined shapes called orbitals.