Chapter 4: Atomic Structure Section 1: Studying Atoms

Ancient Greek Models of Atoms The Greek philosopher Democritus was the first person to put forth a theory that matter was made of tiny particles. He called these particles “atomos”, which is Greek for “uncut”

Ancient Greek Models of Atoms Another Greek philosopher, Aristotle, believed everything was made of only four elements: air, fire, earth, and water.

Dalton’s Atomic Theory John Dalton, a British teacher, developed his atomic theory around 1810. He was the first person to perform experiments and have evidence about atoms.

Dalton’s Atomic Theory Dalton’s Theory: All matter is made of atoms Atoms of the same element weigh the same Compounds are made of more than one type of atom To form compounds, the same types of atoms join together in specific amounts

Thomson’s Model of the Atom J.J. Thomson, a British professor, used a cathode ray tube in an experiment around 1897. This experiment showed that atoms were not solid spheres, but were made of smaller particles.

Thomson’s Model of the Atom Thomson’s model was called the “plum pudding” model. He believed that negative electrons were scattered around inside the positive atom like plums inside a pudding.

Rutherford’s Atomic Theory Click Here

Rutherford’s Atomic Theory Based on the results of his gold foil experiments, Rutherford proposed that atoms had a nucleus. The nucleus is a dense center where all the positive charge in an atom is located.