The History of the Atom
Introductory questions
1. What is an atom?
2. How has the structure of the atom evolved thorugh time?
3. Which is the importance of the Scientific Inquiry for stating a hypothesis?
4. Which experiments led to the discovery of the current atomic model?
400 years B.C, philosophers used to state their theories based on logic instead of observation.
Empedocles said that matter was made of four elements: fire, water, wind and earth.
Democritus and Leucippus, once said that matter was made by tiny particles that cannot be separated nor seen with the naked eye, and they called them atomos (a=no/tomos=parts-division). Aristotle defeated this theory saying that Empedocles theory was right, and there was a fifth element that bring matter to life and powered chemical reactions: Ether. No one mentioned atomos again.
In 1643. Evangelista Torricelli said that air had weight, so it must be made of something physical
Daniel Bernoulli proposed that air was made of tiny particles that moved aside when someone or something moves, and as they stay steady, they fell down like dust.
The Law of Conservation of Mass.
Joseph Priestley and Antoine de Lavoisier studied chemical reactions by burning some materials and established that substances combined or break apart to form new substances, and that mass is not lost or gained during a chemical reaction.
From Dalton to Quantum atomic model
It was in early 1800's that the atom was taken from darkness and set in the eye of science. John Dalton stated the Atomic Theory:
1. Atoms are the smallest part of matter.
2. All atoms of the same element are identical.
3. Atoms cannot be created or destroyed. Atoms combine to form compounds.
4. Atoms combine in defined proportions of whole numbers (just like when doing sandwiches)
J.J. Thomson demonstrated through an experiment with cathode rays that the atom had a positive part and a negative one inserted on the positive mass like raisins in a pie. he called the negative "raisins" Electrons.
Ernest Rutterford demonstrated that the positive part was condensed at the center of the atom arranged in a nucleus, and the electrons orbited around of it.
Physicists stated the Quantum Theory or the study of the inside of the atoms that says: Electrons behave like waves, and fill areas of the atom like sound waves in a room.
Niels Böhr organized the orbits of electrons around the nucleus in energy levels, like the Solar system.
Erwin Schrödinger said that the electrons exist in something called "electron clouds". The size of the shells now relates to the size of the cloud.
