Lesson 3Models of the AtomEarly ModelDemocritus, a Greek philosopher, began the search for a description of matter more than 2400 years ago.His idea: you could keep cutting an object in half, until you reached a point where it could no longer be cut.His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallestpossible piece would be obtained.This piece would be indivisible.He named the smallest piece of matter “atomos,” meaning “not to be cut.”To Democritus, atoms were small, hard particles that were all made of the same material but were differentshapes and sizes. Atoms were infinite in number, always moving and capable of joining together.The idea of atoms as building blocks of matter was suppressed for 2000 years.Modelling the AtomThe first practical model of the atom was developed in the early 1800s by John Dalton. While studying theproperties of atmospheric gases, Dalton inferred that they consisted of tiny particles or atoms. Chemistscontinued to develop the concept of atoms by performing numerous experiments and gathered an abundanceof data. As new discoveries were made, the model of the atom continued to be modifiedSummary of the most important models of the atom and characteristics of the atom is shown below.Models of the Atom - SummaryModelDevelopment of modelBilliard ballDaltonmatter was made up of small particles calledatomsatoms of each element were unique and unlikeatoms of other elementsatoms were indivisibleHis model described the atom as a featurelesssphere.Chocolate chip cookieRaisin bunPlum puddingJ. J. Thomsonused cathode ray tubes to show that atoms couldbe broken down into smaller particlesshowed that negatively charged particles, latercalled electrons, could be ejected from atoms,leaving the atom positively charged.