HOW DID THE ATOMIC MODEL COME ABOUT DEMOCRITUS

HOW DID THE ATOMIC MODEL COME ABOUT? DEMOCRITUS 400 BC • • all matter is made of particles Called Atoms meaning indivisible from Greek word Atomos

JOHN DALTON 1766 -1844 FIRST ATOMIC THEORY The four postulates 1. All matter is made of atoms 2. Atoms of the same element are the same and atoms of different elements are different 3. Atoms cannot be divided, created or destroyed 4. Atoms can combine to form compounds or compounds can separate

JJ THOMPSON 1897 • Atoms are made of smaller parts • Worked with a cathode ray tube and discovered the electron • Developed Plum Pudding Model • Wrong!

ERNEST RUTHERFORD 1912 -1913 • Gold Foil Experiment • Shot + particles through gold foil • A few bounced back from hitting the nucleus • Discovered the Nucleus and that most of an atom is Empty Space around the Nucleus

NEILS BOHR 1913 • Electrons orbit the nucleus in orbits like planets around the Sun • More energy moves electrons to a higher energy level

ELECTRON CLOUD MODEL OF TODAY • Electrons don’t move in definite orbits but have possible energy levels that an electron can occupy. • You have to know the maximum electrons that the first 3 energy levels can hold for elements 1 through 18. (Hydrogen to Argon)

2 electrons in the first layer 8 electrons in the second layer 8 electrons in the third layer (for the top three rows of elements)