2.1 - Atomic Theory

Empedocles

- Stated that there were four fundamental substances: air, water, earth, and fire, that forms the structure of the atom

Democritus

- If the stone is cut into smaller and smaller pieces, it could no longer be divided, and called these small pieces ‘Atomos’

Atomos

- means indivisible

Aristotle

- Accepted the ideas of Empedocles and added his own idea that the four substances could be transformed into other substances

John Dalton (1766-1844)

- British chemist and physicist

- created the Solid Sphere Model

Solid Sphere Model

- Atoms are tiny balls that cannot be broken and are all made of the same material

- All matter is composed of indivisible particles called ‘atoms’

- This theory helped explain how different chemicals mix and what makes them different

- Atoms are dense and solid with no internal structure or subatomic particles

Isotopes

- different proton charges but neutrons stay the same

Deuterium and Tritium

- isotopes of Hydrogen

Law of Conservation of Energy

- matter cannot be created or destroyed, only transferred

J.J. Thompson (1856-1940)

- English physicist known for his work on the nature of electrons

- Discovered the electron in 1897

- Created the Plum Pudding Model

- The total positive charge of the sphere equals to the total negative charge of the corpuscles

Plum Pudding Model

- Atoms are like plum pudding, with tiny positive charges scattered throughout a cloud of negative electrons

- Helped explain why atoms have a neutral charge overall and why they emit light when they collide with each other

Ernest Rutherford (1871-1937)

- New Zealand-born physicist known for his contributions to nuclear physics

- Introduced the Nuclear Model in the early 20th century

Nuclear Model

- First model to propose a central massive nucleus, with the electrons orbiting protons like planets

- Explained the behavior of positively charged alpha particles in the gold foil experiment

- The number of protons is equal to the number of electrons

- Basis of our current understanding of atomic structure

Niels Bohr (1885-1962)

- Danish physicist known for his pioneering work in atomic structure

- Introduced the Planetary Model

Planetary Model

- Electrons move around the nucleus in fixed orbits

- An electron can absorb energy and move to a higher orbit of a larger radius

- An excited electron can fall back to its original orbit by emitting energy as radiation

- Electrons can only exist in certain discrete energy levels

Erwin Schrodinger (1887-1961)

- Austrian physicist renowned for his contributions to quantum physics

- Created the Quantum Model

Quantum Model

- Electrons occupy orbitals, volumes of space around the nucleus with a high probability of finding the electron

- Energy levels are made up of sublevels. Each sublevel contains a set of orbitals. No orbital can contain more than two electrons

- Has a wave-like pattern