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Atomic TheoryDescribing matter and how it behavesThe atomic theory is a THEORY, so it is an explanation of observations supported by reliable evidenceAs new facts become available, this theory is constantly changingAtomic Theory TimelineAbout 2000 years agoGreek Scientists thought matter was made of four elements: earth, air, wind and fireOne Greek, Democritus, did propose eventually a substance being cut would result in a piece that could no longer be cut (called atomos)Aristotle believed the four elements theory, so that one prevailed!Middle agesAlchemy is practicedEarly 1800sResearch leads people to question the four elements theoryJohn Dalton proposes the “Billiard Ball Model” where atoms are small, hard, solid spheres (see pg 25-26)Late 1800sJ.J. Thomson proposes the “Raisin bun” Model and suggests atoms are NOT indivisible but have smaller particles in them (see pg 26)Early 1900sErnest Rutherford performs gold foil experiments and discovers atoms have a tiny dense nucleus with electrons moving around it (see p27)1920sNeils Bohr proposed the concept of electrons being in specific energy levels or shells and having particular amounts of energyPresent Day New technologies are constantly being developedResearch then produces new evidence and allows the model to be developed even further! ................
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