The development of the atomic model

Understanding Atoms and Models

Atoms:

• The building blocks of all matter, forming the basis of all universe's structures and organisms.

• The concept of atoms was invented by Greek philosophers, Democritus and Leucippus, in the fifth century BC.

• Atoms are composed of a positively charged nucleus and negatively charged electrons.

Models of Atoms:

• Models are representations of real-world systems used to understand systems and their properties.

• Atomic models, for instance, represent the structure of an atom based on current knowledge about atom behavior.

• Models are often simplified and not always accurate.

History of Atomic Models

Dalton's Model:

• Proposed that all matter is composed of small, indivisible objects.

• This concept was similar to ancient Greeks' proposal of atoms.

• Electrons and nucleus were unknown at the time.

Thomson's Model:

• Discovered electron in 1897, revealing atoms were smaller than previously thought.

• The "plum pudding model" proposed in 1904, positing atoms as negative electrons floating in a positive charge "soup."

• Thomson won the Nobel Prize in 1906 for his work in this field.

• Despite the model, no understanding of electron arrangement remained.

Marie and Pierre Curie's Discovery of Radioactivity

• Marie and Pierre Curie discovered radioactive elements emitting particles that pass through matter like X-rays.

• Ernest Rutherford revised the atom model in 1911, describing the atom as a dense, positively charged core surrounded by lighter, negatively charged electrons.

• This model, known as the planetary model, was criticized for not explaining the observation that atoms only emit light at certain wavelengths or frequencies.

Niels Bohr's Model of the Atom

• Bohr proposed that electrons could only orbit the nucleus in special orbits at different energy levels around the nucleus.

• This model was later solved by James Chadwick in 1932.

Other Models of the Atom

• Despite the Bohr model, scientists continue to develop new theories on the atom.

• The development of quantum theory, a significant contribution to atomic theory, was made by Schrodinger, Heisenberg, and Born.