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The Atomic Theory Evolution I The Atomic Model Timeline

I) Democritus was an Ancient Greek philosopher. He was one of the first to introduce the term “atoms”. He proposed that:
1. The world was composed of tiny, indivisible, solid objects called atomos.
2. Atomos have different shapes, sizes, and masses.
3. He thought that colors and tastes happened because atomos were combined and connected in different ways.
4. This philosophical concept lacked experimental support.
*Atomos have different shapes, sizes, and masses.

II) John Dalton was a British chemist and physicist who proposed the Solid Sphere Model in 1803. According to his atomic theory:
1. All elements consist of indivisible small particles called atoms.
2. Atoms of the same element have the same mass and properties, while atoms of different elements have different mass and properties.
3. Compounds result from the combination of atoms in simple numerical ratios.
4. Chemical reactions occur when atoms are combined, separated, or rearranged.
5. These principles were supported by experiments.
*Atoms as solid spheres that cannot be broken down into smaller parts.

III) Joseph John Thomson was an English physicist who discovered the electron and proposed the "plum pudding" model in 1897.
1. He demonstrated the existence of electrons and that the electrons were negatively charged.
2. He estimated that electrons were about 2000 times lighter than a hydrogen atom.
3. Atoms are positively charged with negatively charged electrons embedded within, like plums in a pudding.
*An atom is a ball of positive charge with negative electrons embedded in it.

IV) Ernest Rutherford was a New Zealand-born physicist who was known as the “father of nuclear physics”. He conducted the gold foil experiment in 1909, leading to the development of the Nuclear Model. He also discovered the proton. Based on his experiment
1. Atoms have a small, dense, positively charged nucleus.
2. The electrons are located around the nucleus and occupy most of the volume of the atom.
*An atom has a dense, positively charged nucleus at its center, containing protons, while electrons orbit around the nucleus at a distance.

V) Niels Bohr was a Danish physicist who proposed the Planetary Model in 1913. According to his atomic theory:
1. Electrons orbit the nucleus of an atom in specific energy levels or shells.
2. Each energy level can hold a certain number of electrons.
3. As the distance of the electrons from the nucleus increases, their energy also increases.
*The electrons orbit the nucleus, similar to how planets orbit around the sun.

VI) Erwin Schrodinger was an Austrian physicist who proposed the Quantum Model in 1926. Based on his atomic theory:
1. Electrons act like particles and waves.
2. Electrons form clouds of negative charge around the nucleus, exhibiting certain geometrical shapes
3. The exact location and momentum of electrons cannot be simultaneously known
*The electrons are in clouds surrounding the nucleus, and this cloud is less dense.

Throughout the history of atomic theory, various scientists have contributed to our understanding of the fundamental nature of matter. In 400 BC, Democritus proposed the concept of "Atomos," suggesting that atoms are the basic building blocks of matter, and the shape of an atom explains the behavior of elements. In 1803, John Dalton introduced the "Solid Sphere" model, positing that an atom is a solid, indivisible sphere. Moving forward to 1897, J.J. Thomson presented the "Plum Pudding" model, suggesting that negative electrons are embedded in a sea of positive charges. In 1911, Ernest Rutherford proposed the "Nuclear" model, asserting that positive charges are concentrated within a central nucleus. Niels Bohr, in 1913, introduced the "Planetary" model, describing electrons restricted to circular orbits with different energy levels. Finally, in 1926, Erwin Schrödinger put forth the "Quantum Model," which suggests that electrons exist in clouds surrounding the nucleus, and these clouds are less dense. These sequential advancements in atomic models have shaped our understanding of the microscopic world.

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