Atomic Models study guide

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Atomic Models study guide

Atomic Models

Atoms – the building blocks of matter.
Scientists began to study using indirect evidence – observations of how something behaves without seeing or actually touching the subject. Similar to how you figure out a present before you even open it.
A model – uses familiar ideas to explain unfamiliar facts observed in nature.

Democritus: no model name – Greek (460 B.C.) He concluded that matter could not be divided into smaller pieces forever. That eventually the smallest piece would be obtained. This piece would be indivisible and he named it the atom (which means indivisible).

Atomists – Greek philosophers that shared his idea… very few did.

Dalton: Dalton’s model – English (early 1800’s) He concluded that all elements are composed of atoms, that atoms of the same element are exactly alike, and that compounds are formed by the joining of atoms of two or more elements.

Thomson: Plum Pudding Model- English (1897) Studied the passage of an electric current through a gas and discovered electrons. Now he knew that the atom was divisible! He called the negative particles corpuscles. This led the scientists to a new question because they knew the atom was neutral.

His model said that there was a pudding-like substance that was positively charged and the negatively charged particles moved about in it. Looks like a chocolate chip cookie…

Rutherford: Rutherford’s model- British (1911). He proposed that all of the atom’s positively charged particles (protons) were contained in the nucleus. The negatively charged electrons were scattered outside the nucleus around the edge. That between the nucleus and the electrons there was lots of empty space.

Bohr: Bohr’s model – Danish (1913) He said that electrons move in definite orbits around the nucleus, much like the planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus. The strongest away from the nucleus.

The Modern Model – (also known as the Wave Model) An atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make the atom neutral. It is a combination of Rutherford’s and Bohr’s models. Basically the number of protons equals the number of electrons.

Remember:

Democritus: Indivisible piece of matter called the atom
Dalton: Elements made of atoms all alike & compounds made of 2+ elements
Thomson: Discovered electrons, atoms divisible, pudding model
Rutherford: Protons in nucleus, electrons scattered around outside
Bohr: electrons move in orbits around nucleus, strongest ones far away from nucleus
Wave: small positive nucleus surrounded by electrons (same # as protons)

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