1. Modern Atomic Theory
Grade 9 Science Chemistry

2. Modern Atomic Theory
Atoms are made of 3 particles; protons, neutrons and electrons
Atoms have a nucleus that is made of protons and neutrons with electrons orbiting around it.
Protons and electrons have opposite charges, therefore, they attract.
This attraction holds the electrons around the nucleus.

3. Elements vs. Compounds
An element is a pure substance made up of one type of particle, or atom. Each element has its own distinct properties and cannot be broken down into simpler substances by means of a chemical change.
Compounds are pure substances that are made up of two or more elements chemically combined together. They can be broken down into elements again by chemical means.

4. Difference Between Theories and Laws
Laws do not explain anything . They just describe and summarize what happens.
Theories are imaginative ways to explain why something happens.

5. Democritus
Around 400 BC, a Greek philosopher named Democritus suggested the first atomic theory
He explained that all things are "composed of minute, invisible, indestructible particles of pure matter which move about eternally in infinite empty
Even though there was no technology to help research Democritus‘s theory, he was very precise
John Dalton, J.J. Thompson, Ernest Rutherford, Niels Bohr, and Ernest Schrodinger all contributed significantly to the modern atomic theory by finding the actual evidence.

6. John Dalton Lived from 1766-1844
Was one of the earliest scientists to contribute to the modern atomic theory.
Dalton’s Theory  
All elements are composed of atoms.
All atoms of the same element are identical – in particular they have the same mass.
The atoms of one kind of element are different from the atoms of all other elements - in particular the atoms of one element have a different mass than those of other elements.
Atoms are indestructible and retain their identity in chemical reactions.
Compounds are formed by joining atoms in specific whole number ratios.

7. J.J Thompson Lived from 1856-1940
Won a noble prize for his great work on the electron.
Realized that if there ware negative parts to atoms, then there must be positive parts as well to balance it, because most matter is neutral.
His theory of electron distribution inside an atom was later proved to be incorrect by Ernest Rutherford.
In 1897,discovered first subatomic particle, a component of all atoms, the electron

8. Ernest Rutherford Lived from 1871 – 1937 Made blueprints of an atom.
Said to be the father of nuclear physics.
Said that radiation was caused by the destruction of atoms and that the alpha particle is the helium nucleus.

9. Niels Bohr Lived from 1871 - 1937 Discovered the proton in 1910
Won the 1922 Nobel Prize for physics, mainly for his work on the structure of atoms

10. Erwin Schrodinger Lived from 1887 to 1961
Viewed electrons as continuous clouds
Introduced "wave mechanics" as a mathematical model of the atom.