Atomic Structure
Definition
What is an atom?
• An atom is the smallest building block of matter. Atoms
are made up of things called protons, neutrons, and
electrons.
• Protons are positively charged, neutrons have no
charge, and electrons have a negative charge.
• There are 100’s of different types of atoms. The reason
why is because there are things called isotopes.
• Isotopes are variations of an atom to form the same
element but in a different way.
• In every atom there is a nucleus.
Timeline
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5th Century: Democritus (a Greek philosopher) who came up with
the theory of atomic structure. Plato and Aristotle rejected the idea.
1803: John Dalton proposed an atomic theory with spherical solid
atoms based upon measureable properties of mass.
20th Century: J.J. Thomson discovered the electron, via an
experiment with cathode ray tubes.
1909: Robert Milliken did an oil drop experiment to determine the
charge and mass of the electron.
1922: Neils Bohr develop an explanation of atomic structure that
underlines the regularities of the periodic table.
Mid 1920’s: Erwin Schrodinger and Werner Heinsberg come up with
an idea that became the cloud model. The cloud model says that
electrons exist in different areas around the nucleus.
Structure and How it changed
Rutherford Model
Bohr Model
Cloud Model