“Billiard Ball” Model

Year：1803

Who：English Chemist John Dalton

Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. 

Dalton added these so the model atoms could be joined together with hooks and used to model compounds.

This is a rudimentary understanding of the atomic model. It is one of the most important theories in all of science.

experiments 

He investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny, individual particles that are in constant, random motion.

He researched the properties of compounds, which are substances that consist of more than one element. He showed that a given compound is always comprised of the same elements in the same whole-number ratio and that different compounds consist of different elements or ratios. 

Result：Only if elements are made of separate, discrete particles that cannot be subdivided.

Theory/law proposed

 ”Plum pudding“ model

First proposed by J. J. Thomson in 1904. The plum pudding model is defined by electrons surrounded by a volume of positive charge.

A substance is consists of small spheres which are having the radius of about 10-10 m in diameter. The positive charge is spread uniformly throughout the volume of sphere called pudding. The negatively charged particles Electrons called Plums are distributed as point charges in shells. Like plums embedded in a pudding (hence the name).

Experiment

Cathode ray tubes are sealed glass tubes from which most of the air has been evacuated.

 A high voltage is applied across two electrodes at one end of the tube, which causes a beam of particles to flow from the cathode (the negatively-charged electrode) to the anode (the positively-charged electrode).

 The tubes are called cathode ray tubes because the particle beam or "cathode ray" originates at the cathode. 

The ray can be detected by painting a material known as phosphors onto the far end of the tube beyond the anode. 

The phosphors spark, or emit light, when impacted by the cathode ray.

Theory/law proposed

the atom is mostly empty space with a tiny, dense, positively-charged nucleus.

rather than being composed of light, they were made up of negatively charged particles he called “corpuscles”. 

Upon measuring the mass-to-charge ration of these particles, he discovered that they were 1ooo times smaller and 1800 times lighter than hydrogen. 

Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.