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Scientists Behind Atomic Theory (Aristotle (Greek philosopher, disagreed…
Scientists Behind Atomic Theory
Democritus
Greek philosopher
Thought that you could eventually end up with a particle that could not be cut
Called this particle atomos, a Greek word meaning "not able to be divided"
Did not do experiments to test his theory
400 BCE
Aristotle
Greek philosopher
disagreed with Democritus
Did not believe that suck a particle could make up all substances found in nature
Did not do experiments to test his theory
400 BCE
John Dalton
Theory based on evidence from experiments
Dalton's theory
all matter is made up of atoms
Atoms cannot be created, divided, or destroyed
all atoms of a certain element are identical, but different from atoms of all other elements
Every substance is made up of atoms combined in certain ways
1808, British chemist
J.J. Thomson
experiments provided evidence that atoms are made up of even smaller particles
Found particles within the atom that have a negative charge
These negatively charged particles late known as electrons
1897
Thought that an atom was a positive sphere with the electrons mixed through it
Ernest Rutherford
1909
conducted an experiment to study the parts of the atom
Experiment suggested that atoms have a nucleus
Nucleus: small dense center that have a positive charge and is surrounded by moving electrons
Later discovered that the nucleus is made up of smaller particles
Called positively charged particles in nucleus: protons
Niels Bohr
1913
made observations that led to a new theory of how the electrons in the atom behaved
Agreed that an atom has a positive nucleus surrounded by electrons
In his model, electrons move around the nucleus in circular paths
Each path is a certain distance from the nucleus
His model helped scientists predict the chemical properties of elements
Scientists have since made observations that cannot be explained by Bohr's model
James Chadwick
Rutherford's student
1932
discovered that nucleus contains uncharged particles called neutrons
current atomic theory- electrons do not move in circular paths around the nucleus
instead, electrons move within an area around the nucleus called the electron cloud