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Democritus
Indivisible Particles: Democritus proposed that all matter is composed of tiny, indivisible particles called “atomos” (meaning “indivisible” or “uncuttable” in Greek)
Different Types of Atoms: Democritus suggested that there were different types of atoms, each with its own unique size, shape, and properties.
Constant Motion: Democritus believed that atoms were constantly in motion, and their interactions with each other led to the formation of different substances.
Empty Space: Democritus also introduced the concept of “the void” or empty space, which allowed atoms to move freely.
It’s important to note that Democritus’ atomic theory was largely speculative and lacked experimental evidence
John Dalton
Father of the Modern Atomic TheoryAll matter is made up of extremely small particles called atoms.
Atoms of the same element are identical in size, mass, and properties BUT different from atoms of another element
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple, whole number ratios to form compounds.
In chemical reactions, atoms are rearranged, combined, or separated.
Ernest Rutherford
Worked with gold foil - called the Gold Foil experiment
Conclusion of the experiment:
Most of the space in an atom is empty.
Atom has a positive dense center called nucleus.
Led to the discovery of the proton
Joseph John (JJ) Thomson
Worked on the Cathode Ray Tube experiment
Led to the discovery of the electron
His model of the atom was called the “Plum Pudding” model
Erwin Schrodinger
He changed the concept of orbit into orbitals. This is model we are using right now.
Neils Bohr
Quantised orbits - Electrons revolve around the nucleus in a certain selected path called orbits (energy levels) number as 1,2,3,4 and designated as K,L,M.N.
As long as the electron remains in a particular orbit it does not change its energy.
When an atom gains energy, electrons jumps from lower energy levels to higher energy levels.
James Chadwick
Discovered the neutron
