chemistry

democritus

460

he created the first atomic model.

dalton's atomic theory

Oct 30, 1803

Atomic theory proposed by John Dalton
Dalton's theory was based on the premise that the atoms of different elements could be distinguished by differences in their weights. He stated his theory in a lecture to the Royal Institution in 1803. The theory proposed a number of basic ideas: All matter is composed of atoms
Atoms cannot be made or destroyed
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are rearranged
Comp

Thomson Atomic Theory

Oct 29, 1897

1. An atom consists of a sphere of positive charge with negatively charged electron embedded in it,
2. The positive and the negative charges in an atom are equal in magnitude, due to which an atom is electrically neutral. It has no over all negative or positive charge.

We can compare the Thomson’s atomic theory model with a water melon. The red edible part of a water melon represents the sphere of a positive charge where as the black seeds embedded in it is like the electrons.

modern atomic theory

Oct 30, 1900

A theory of the structure and behavior of atoms has taken more than two millenia to evolve, from the abstract musings of ancient Greek philosophers to the high-tech experiments of modern scientists. However, prior to the scientific revolution and the development of the scientific method starting in the 16th century, ideas about the atom were mainly speculative. It wasn't until the very end of the 19th century that technology became advanced enough to allow scientists a glimpse of the atom's cons

rutherford atomic theory

Oct 31, 1911

Rutherford tested Thomson's hypothesis by devising his "gold foil" experiment. Rutherford reasoned that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. Then, if he shot high velocity alpha particles (helium nuclei) at an atom then there would be very little to deflect the alpha particles. He decided to test this with a thin film of gold atoms. As expected, most alpha particles went right through the gold foil but to his amazement a few alpha particles

bohr atomic theory

Oct 31, 1913

In 1913 Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. The motion of the electrons in the Rutherford model was unstable because, according to classical mechanics and electromagnetic theory, any charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus. To remedy the stability problem, Bohr modified the Rutherford model by requiring that the el