The History of Atomic - Model

Aristotle (350 B.C.) disagreed with Democritus's model of the atom in Aristotle was a Greek philosopher. Many of his ideas were more thought based than scientifcially based. For this reason, Aristotle strongly disagreed with Democritus. He felt that there was no smallest part of matter and that different substances were made of earth, fire, air, and water. Aristotle did not have an atomic model due to the fact that he thought atoms did not exist.

Democritus was the first scientist to create a model of the atom. He was the first one to discover that all matter is made up of invisible particles called atoms. He created the name "atom" from the Greek word "atomos", which means uncuttable. He also discovered that atoms are solid, insdestructable, and unique. HIs model was just a round solid ball. Democritus didn't know about a nucleus or electrons, all he knew was that everything is made of atoms.

Lavoisier was a French nobleman that founded several elements and put the first table of elements together. He used Aristotle's ideas of fire, earth, air, and water to create experiments invesigating combustion and oxidation. By using previous knowledge of atomic bonding, he discovered important elements like oxygen, hydrogen, and sulfur. He discovered that water was made of oxygen and hydrogen, and air included nitrogen. Lavoisier also created the first chemistry textbooks and tables.

Dalton's atomic theory

John Dalton (1766-1844)

John Dalton developed an atomic theory in the 1800s. He did experiments, worked out some atomic weights and invented symbols for atoms and molecules. His most important conclusions are summarised below:

• All matter is made of atoms
• Atoms cannot be broken down into anything simpler
• All the atoms of a particular element are identical to each other and different from the atoms of other elements
• Atoms are rearranged in a chemical reaction
• Compounds are formed when two or more different kinds of atoms join together

Dalton's theory was developed and changed as new evidence was discovered.

JJ Thomson's discovery of the electron

JJ Thompson discovered the electron in 1897. This showed that the atom contained smaller pieces, whereas Dalton had thought that atoms could not be broken down into anything simpler.

Rutherford's nuclear atom

In 1911 Ernest Rutherford used experimental evidence to show that an atom must contain a central nucleus. This was further evidence that an atom contained smaller pieces.

Bohr's electron orbits

Niels Bohr further developed Rutherford's nuclear atom model. He used experimental evidence to support the idea that electrons occupy particular orbits or shells around the nucleus of an atom.

The development of the theory of atomic structure is an example of:

• How a theory may change as new evidence is found
• How a scientific explanation is provisional but may become more convincing when predictions based on it are confirmed later on.

Marie and Pierre Curie were a European couple that contributed to atomic chemistry by exploring the mysteries of radioactivity. After radiation was discovered by Henri Baquerel, Marie decided to look further into this discovery. Through this she and her husband discovered the elements radium and polonium and won the Nobel Peace Prize for their works in radioactivity. Her discovery later added to the atomic model.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/atomstrucrev5.shtml