is for Atom

is for The earliest history

The matter is composed of indivisible building blocks. This idea was recorded as early as the fifth century BCE by Leucippus and Democritus. The Greeks called these particles atomos, meaning indivisible, and the modern word “atom” is derived from this term.

The atom first discovered

Around 450 B.C., the Greek philosopher Democritus introduced the idea of the atom. However, the idea was essentially forgotten for more than 2000 years. In 1800, John Dalton re-introduced the atom.

is for SOLID SPHERE MODEL

Dalton model (1803) The atom is a hard, solid ball

John Dalton, an English natural scientist, proposed the world's first atom.

The theory of

① Atoms are all indivisible particles. ② Atoms of the same element have the same properties and masses; ③ An atom is a tiny solid sphere.

is for PLUM PUDDING MODEL

The plum pudding model is an atomic structure model proposed by Joseph Thomson in 1904.

        In 1897, Joseph Thomson made his breakthrough discovery of the existence of electrons from cathode rays. After this historic discovery, he began to oppose the Dalton model of the atom. He didn't think atoms were indivisible; Contained within the atom are negatively charged electrons that can be removed from the atom. In 1904, Thompson created the plum pudding model of the atom.

In 1909, Hans Geiger and Ernst Marsden (Jishi.Y), under the guidance of Ernest Rutherford, bombarded thin gold foil with alpha rays and found that most of the alpha particles were shining straight through However, the deflection is very small. According to the raisin bun model, all alpha particles should be bounced back instead of passing through the “wall”.

Alpha particle scattering experiment

In 1911, British physicist Rutherford proposed a planetary model of atomic structure based on the alpha particle scattering experiment. He believed that electrons revolve around the nucleus like planets in the solar system revolve around the sun. But the planetary atom model is obviously contrary to the actual situation.

Progress of each model

SOLID SPHERE MODEL

Recognized atoms of a particular element differ from other elements

Atom aren't indivisible-They're composed from subetomic particles

PLUM PUDDING MODEL

Recognized Electrons as components of atoms

No nucleus; Didn't explain later experimental observations

is for NUCLEAR MODEL

The nuclear shell model was independently proposed by Mrs. Meyer and Jansen in 1949. The structure of atomic nuclei can be borrowed from the structure of atomic shells, because there are a series of magic number nuclei in nature, that is, nuclei are particularly stable when the number of protons and neutrons equals the magic number respectively

In 1912, on the basis of the Rutherford planetary model, Bohr introduced Planck's quantum concept, assuming that the orbits of electrons outside the nucleus are separated and discontinuous, that is, quantized. Bohr's quantum orbital atomic model successfully solved the problem of the stability of the atomic structure and the law of the hydrogen atom's spectral lines.