Atomic Theory and Early Models of Matter

Atomic Theory

• All matter is composed of atoms.
• Atoms are indivisible.
• All atoms of the same element are identical.
• Atoms of different elements differ from each other.
• Compounds form when two or more elements combine.

Law of Conservation of Mass

• Matter cannot be created or destroyed, only transformed.
• The mass of a substance never changes, but its weight can change due to gravity.

John Dalton

• Proposed the Atomic Theory, suggesting that atoms are indivisible and solid, positively charged spheres.
• Dalton's experiments determined that substances are composed of specific proportions of atoms.
• His model is known as the Billiard Ball Model.

J.J. Thomson

• Discovered electrons (negatively charged particles) within a positively charged solid sphere.
• Thomson's model is known as the Plum Pudding Model.
• Used the Cathode Ray Tube to demonstrate that a positively charged plate attracts a beam of light, proving that the beam must be negatively charged.
• He called the negatively charged particles "corpuscles," later named electrons.

Ernest Rutherford

• Demonstrated that atoms have a positively charged nucleus containing most of the atom's mass, surrounded by empty negative space.
• His experiments used alpha particles to bombard gold foil.