Examine the history of the development of the atom. We have already discussed the major players in the development of the atom. Pick out at least 8 major players who helped aid in the development of the concept of the atom. Explain each experiment in a concise explanation. Then explain how each one aided in the development of the next or how their concept assisted in the further development of the current quantum model of the atom.


Democritus- Democritus stated that matter was composed of small particles called atoms. "The only differences between them is their size, shape and weight."

John Dalton- he made the 5 laws about atoms listed below. they helped the concept of atomic wieghts.

"1. Matter is made up of indivisible atoms.
2. All atoms of an element are identical.
3. Atoms are neither created nor destroyed.
4. Atoms of different elements have different weights and chemical properties.
5. Atoms of different elements combine in simple whole numbers to form compounds."

Mendeleev- he Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law. he also helped arrange the periodic table.

J.J. Thompson-
Found that cathode rays could be deflected by an electric field Showed that cathode "rays" were actually particles
Raising Pudding Model -
Matter is electrically neutral and electrons are much lighter than atoms.
Conclusion: There must be positively charged
particles which also must carry the mass of the
atom. Dalton's model is now incorrect because
atoms are divisible.

Rutherford- Studied absorption of radioactivity.

"* Alpha radiation - positive charge - absorbed by a few hundredths of a cm or metal foil
*

Beta radiation - negative charge - could pass through 100x as much foil before it was absorbed
*

Gamma rays - no charge - could penetrate several cm of lead

Rutherford was also able to estimate the charge of an atom by studying the deflection of alpha particles. He found that the positive charge on the atom was approximately half of the atomic weight."

Bohr- helped to understand atomic structure and quantum mechanics and came up with the Bohr model of the atom.

Mosely- arranged the periodic table based on atomic number. this helped later scientists.

Chadwick- "discovered neutron with radioactivity -

"* Proved that neutrons, neutral particles in the nucleus that made up approximately
half the mass of an atom, did exist."

"Atomic Rules

* The number of protons in the nucleus of an atom is equal to the atomic number (Z).
* In a neutral atom, the number of electrons is equal to the number of protons.
* The mass number (M) of an atom is equal to the sum of the number of
protons and neutrons in the nucleus.
* The number of neutrons is equal to the difference between the mass number (M)
and the atomic number (Z)."
sources - wikipedia (quoted text)