This is a topic for General Chemistry subject.

1. ATOMS FROM THE EYES
OF PHILOSOPHERS AND
SCIENTISTS

2. I. Philosophers
A. Empedocles (450 BC)
 Asserted that all things are composed of primal elements:
earth, air, fire, and water

3. B. Democritus (400 BC)
 Believed that all matter have very small particles called
atoms from the Greek word atomos which means
“invisible” or “ uncuttable”

4. C. Aristotle (around 380-320 BC)
 Supported Empedocles idea, & he added fifth element
called aether or ether
 Thought that all matter was continuous & can be further
divided into smaller and smaller pieces infinitely
 His idea is accepted and greatly influenced alchemists
until end of 17th century

5. II. Scientists
A. John Dalton (1808)
 Formulated the atomic theory and proposed the law of
multiple proportions

6. Dalton’s Atomic Theory
1. Elements are made of small particles, called atoms.
2. All atoms of particular elements are identical.
3. Atoms of different elements combine simple whole-
number ratios to form chemical compounds.
4. In chemical reactions, atoms are combined , separated
or rearranged.

7. Dalton’s third hypothesis supports the
following:
 Law of definite proportions
Joseph Proust suggested that when a product is formed,
elements always combine in similar proportions by mass
regardless of the size of the sample.

8.  Law of multiple proportions
If two or more compounds are composed of the same
elements, then the ration of the masses of the second
element combined with certain mass of the first element
always a ratio of small numbers

9. Dalton’s last hypothesis points the:
 Law of conservation of mass
When a reaction is done (e.g. in a closed container), the
total before and after the reaction is the same

10. B. Dmitri Mendeleev (1869)
 Arranged the known elements in the Periodic Table
based on their atomic mass

11. C. Antoine Bequerel, Marie Curie
(1890s)
 Observed the radioactive materials cause the atoms to
break down spontaneously

12. D. Wilhelm Röntgen (1895)
 Discovered X-rays

13. E. John Joseph Thomson (1897-
1904)
 Discovered the electrons that have negative charge.
The charge is equal to -1.6022 x 10−19 found by Robert
A. Millikan.
 Suggested the plum pudding model - negative electron
in a positive structure

14. F. Ernest Rutherford (1910-1919)
 Observed that atoms are mostly empty space through
the results of his gold foil experiment in 1911
 Discovered protons that have positive charge.

15. Rutherford’s experiment

16. G. Niels Bohr (1913)
 Came up with a model that shows electrons move in
orbits

17. H. Henry Moseley (1913)
 Developed applications of X-ray spectra to study atomic
structure

18. I. James Chadwick (1932)
 Proved the presence of neutral subatomic particles,
which he called neutrons

19. THE END
Prepared by:
OLAYVAR, JUBIL JOHN C.
STEM 11-G