The Atomic Theory. The Atom Protons and Neutrons.

The Atomic Theory

The Atom

Protons and Neutrons

Atom

An atom is the smallest particle into which an element can be divided and still be the same substance.

Atomic Theory

The existence of atoms is not a new idea. Atomic theory has been around for more than 2,000 years. A theory is a unifying explanation for a broad range of hypotheses and

observations that have been supported by testing.

John Dalton

All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.

Atoms of the same element are exactly alike, and atoms of different elements are different. Atoms join with other atoms to make new substances.

J.J. Thomson

Thomson discovered that there are small particles inside the atom. Therefore, atoms can be divided into even smaller parts.

JJ Thomson is credited with discovering “ELECTRONS”

Ernest Rutherford

Rutherford proposed that in the center of the atom is a tiny, extremely dense, positively charged region called the “NUCLEUS”.

James Chadwick

The Neutron, one of the particles in the “Nucleus” of an Atom, is discovered by British physicist James Chadwick.

Niels Bohr Bohr suggested that electrons traveled around the nucleus in definite paths. He proposed

that no paths are located between the levels, but electrons can jump from a path in one level to a path in another level. (A very good example of this would be a “ladder”.)

The Modern Theory

According to the current theory, electrons do not travel in definite paths as Bohr suggested. In fact their paths can not be predicted. Regions inside the atom where electrons are likely

to be found are called “ELECTRON CLOUDS”.

Rutherford’s Model

Bohr’s Model

The Modern Theory

Do You Remember?

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Questions 1-5