By: Sachi Khemka

Some points

of interest.

**** The model of the atoms changing throughout history**** The contributions of many men towards the discovery of the atom**** Each philosophers, scientists, etc. theory on the atom, and their model Ex: - Democritus - Aristotle - Bohr

AristotleHe found that matter is made of atoms. He also found that matter will always exist. He also found 4 elements, fire, water, earth, and air. With all this, he came up with the theory of motion.

Democritus• This is the Greek philosopher

Democritus who began the search for a description of matter more than 2400 years ago.

• Proposed an Atomic Theory which states that all atoms are small, hard, indivisible and indestructible particles made of a single material formed into different shapes and sizes.

• Found that atoms are not all the same, they are eternal, and always moving

• Aristotle did not support his atomic theory

This was Democritus’ idea of an atom which was forgotten for over 2,000 years

Antoine Lavoisier Named oxygen and

hydrogenHe invented the first

periodic table, which had 33 elements.

Known as the “Father of Modern Chemistry”

He also proposed the Law of Conversation of Mass which represents the beginning of modern chemistry, which states, in a chemical reaction, matter is neither created nor destroyed

FIRST PERIODIC TABLE!

John Dalton

A brilliant youth that he became an English school teacher when barely 12 years old

Atomic theory of matter based on his experimental observations. :

*All matter is made of atoms. Atoms are indivisible and indestructible. *All atoms of a given element are identical in mass and properties. * Compounds are formed by a combination of two or more different kinds of atoms. * A chemical reaction is a rearrangement of atoms. * Atoms can be neither created nor destroyed. This theory became one

of the foundations of modern chemistry

This is Dalton’s model of an atom, is once again compared to the billiard ball, and similar to Democritus’ model.

J.J Thomson• Proved that an atom

can be divided into smaller parts.

• In 1897, proposed the Plum Pudding Model. Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding.

Ernest Rutherford Performed the Gold

Foil Experiment and suggested the following characteristics of the atom:

**It consists of a small core, or nucleus, that contains most of the mass of the atom **This nucleus is made up of particles called protons, which have a positive charge **The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space “Father of Nuclear

Physics” Was on the New

Zealand $100 bill

1. Some “bullets” went straight through the gold foil without changing its course

2. Some did bounce away from the gold sheet as if they had hit something solid

3. Atoms were not a pudding filled with a positively charged material.

4. Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.”

Niels BohrProposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in paths.

The electrons can jump from a path in one level to a path in another level (depending on their energy level)

Let’s draw a Bohr Model!

Protons: 36Neutrons: 48

Erwin Schrodinger

He further explained the nature of electrons in an atom by stating that the exact location of an electron cannot be stated; therefore, it is more accurate to view the electrons in regions called electron clouds; electron clouds are places where the electrons are likely to be found

James Chadwick

Realized that the atomic mass of most elements was double the number of protons which resulted in discovery of the neutron in 1932

Worked with Ernest Rutherford

400 BC

Now- The Wave Model- Electrons do not have a

defined path, they are in an electron cloud

- Small positively charged nucleus surrounded by a large region filled with electrons. (Wave Mechanics)