1. A TIMELINE of the MAJOR SCIENTISTS and THEIR CONTRIBUTIONS
ATOMIC STRUCTURE
A TIMELINE of the MAJOR SCIENTISTS and THEIR CONTRIBUTIONS

2. 490 BC
DEMOCRITUS
“atomos”
First to propose that matter is composed of tiny, indivisible particles called “atomos” or atom.

3. JOHN DALTON “billiard ball” model
490 BC
1808
JOHN DALTON
“billiard ball” model
Atoms are tiny, hard and indestructible spheres

4. JOSEPH JOHN THOMSON “raisin bread” model
490 BC
JOSEPH JOHN THOMSON
“raisin bread” model
1808
1897
Atoms are composed of positive sphere (“bread”) and negative charges or electrons (“raisins”)
Did not identify the number of electrons nor the nature of positive sphere

5. THOMSON’S “RAISIN BREAD” MODEL OF THE ATOM

6. CATHODE RAY TUBE (CRT)

7. ERNEST RUTHERFORD “nuclear model”
490 BC
ERNEST RUTHERFORD
“nuclear model”
1808
1897
1911
Atom has a small, dense and positively charged center called the nucleus. Moving around it would be the negatively charged electrons. Therefore the atom is mostly empty space.

8. RUTHERFORD’S NUCLEAR MODEL OF THE ATOM

9. RUTHERFORD’S GOLD FOIL EXPERIMENT

10. NIELS BOHR “planetary model”
490 BC
1808
1897
1911
1913
NIELS BOHR
“planetary model”
Electrons move in definite orbits around the nucleus based on their energy levels. The farther the electrons are from the nucleus, the greater is their energy level.

11. BOHR’S PLANETARY MODEL OF THE ATOM

12. “wave or electron cloud model”
490 BC
1808
1897
1911
1913
1926
ERWIN SCHRODINGER
“wave or electron cloud model”
Electrons are moving around the nucleus in an area known as the electron cloud. It is possible to know the area where the electron is based on its energy level but not its exact location.

13. SCHRODINGER’S WAVE OR ELECTRON CLOUD MODEL

14. Cl - 35 CHEMICAL NOTATION 17 MASS NUMBER = p+ + no CHARGE = p+ - e-
no = MASS NUMBER – ATOMIC NUMBER
e - = p+ - charge
no = = 18
e- = 17 – (-1) = 18
MASS NUMBER = p+ + no
CHARGE = p+ - e- - 35 Cl 17
CHEMICAL SYMBOL
ATOMIC NUMBER = p+