1. ENGR. RJAAGUILAR
COLLEGE OF ARTS AND SCIENCES

2.  Interpret the classical laws of chemical
combinations using Dalton’s Atomic Theory
Cite experimental evidence for the existence
of subatomic particles
 List the three fundamental particles of
matter and describe their charges and
relative masses
 Use the properties of sub‐atomic properties
to determine atomic structure

3. Laws of Chemical Combinations
Atomic Theory
Fundamentals of the Elementary
Particles
Introduction to the Periodic
Table

4. Matter was
composed of 4
fundamental
substances:
FIRE,
EARTH,
WATER, AIR

5. Leucippus Democritus

6. •Leucippus
•5th century
-was one of the earliest Greeks to
develop the theory of atomism -
everything is composed of
various imperishable, indivisible
elements called atoms - was
elaborated in greater detail by his
pupil and successor,Democritus.

7. •Democritus
•5th BC
-first to propose that matter
was made up of tiny
indivisible particles called
“atomos” meaning indivisible/
cannot be cut/destroyed.

8. The next 2000 years of chemical history were
dominated by ALCHEMY, a pseudoscience
-ancient art practice during
Middle Ages.
-discover substance that
would transmute metals into
gold/silver and to find means
of prolonging human life
-predecessor of modern
science (particularly
chemistry)

9. - summarize two of the
consistently observed patterns of
the behavior of matter
Law of Conservation of Mass
 Law of Definite Proportions

10. Antoine Laurent Lavoisier
(1743-1794)
• “Law of Conservation of Mass “
• In a chemical reaction, the total
mass of the materials that
reacted (reactants) is equal to
the total mass of the materials
that were produced
(products).

11. Joseph Louis Proust (1754-1826)
• “Law of Definite Proportions “
• Any pure sample of a chemical
compound, from whatever source
and however prepared, always
contains the same elements and
always in the same proportions
by mass.

12. John Dalton (1766-1844)
• In 1808, published the book A
New System of Chemical
Philosophy wherein he
presented the atomic theory in
detail.
• “Law of Multiple Proportion “

13. 1. Matter consists of tiny particles called atoms
which are indestructible.
2. All atoms in a given element are identical
and have the same mass. Atoms of different
elements have different properties.
3. Reactions involve only the rearrangement of
atoms.
4. When atoms combine to form compounds,
the ratio of the no. of combining atoms is
fixed.

14. 1. All matter is composed of extremely small,
indestructible particles called atoms.
-hard, indivisible spheres, no parts
(Billiard Ball Model)
NOTE:
We now know that atoms are NOT indestructible.
They consist of still smaller particles.

15. 2. All atoms of a given element are identical, in
mass and other properties.
Atoms of one element differ from the atoms of
all other elements.
NOTE:
We now know that atoms of a given element
may differ. Some elements have several
isotopes

16. 3. Compounds are formed by the combination of the
atoms of different elements in fixed proportions.
NOTE:
Some compounds may have the same composition but
the atoms combine in different ways.
Example: benzene

17. 4. A chemical reaction involves the
rearrangement of atoms. No atoms are
created, destroyed.
NOTE:
In some reactions, atoms may break apart in
that some may lose electrons. But atoms do
not break apart to produce other atoms.

18. (Dalton’s contribution to the laws of chemical
combination)
“If two elements A and B can combine to form
two or more compounds, and if the weight of
A in the different compounds is kept
constant, then the weight of B in these
compounds are in the ratio of small integers.”

20. Nitrous oxide N2O
Nitric oxide NO
The mass ratios are related by small whole
numbers because the ratios of combining
atoms are related also by small whole
numbers.

21. How does the Atomic Theory help us
understand matter?
The Atomic theory gives us a mental picture of
matter.
 Atoms are the building blocks of elements,
compounds and mixtures.

22. Starting the 1800’s, evidences started to emerge
that show matter (and therefore the atom) is
electrical in nature

23. • Joseph John Thomson
• (1856-1940)
- His experiment in1897 led to the
discovery of a fundamental
building block of matter.
Made use of a piece of equipment
called a cathode ray tube.
vacuum tube - all the air has been
pumped out.

25. • The cathode rays are repelled by the negative
pole of a magnetic field
This suggests that the ray consists of a stream of
negatively charged particles
• It correctly suggested that the atom consists
of an arrangement of (+) and (–)charges.
• It postulated the presence of the electron in
all matter

26. “plum pudding” model: raisins dispersed in pudding.
• An atom is a diffuse, spherical cloud of positive
electrification with randomly embedded negatively
charged electrons.

27. • Robert Millikan
• (1868-1953)
Measured charge of e-(1923 Nobel
Prize in Physics)

29. Charge to mass ratio (Thomson):
e/m = -1.76 x 108 C g-1
Charge of the electron* (Robert Millikan,1909):
e = -1.60 x 10-19C
*designated as 1 unit of charge; by convention, the
charge of the electron is given as –1.
Mass of the electron, m = 9.1 x 10-28g
Mass of the hydrogen atom –about 10-24g
The electron is about 2000x lighter than the hydrogen
atom.

30. • Antoine Henri Becquerel
• (1852-1908)
Discovered radioactivity in
1896

31. Components of the natural
emitted radiation
(radioactivity)
• Alpha (α) particles –charge
of +2; mass about 7300x
that of the electron
• Beta (β) particles –later
identified as electrons
• Gamma (ϒ) rays –a form of
high-energy EM radiation

32. • Ernest Rutherford
• (1871-1937)
-believed in the Plum Pudding
Model
Used radioactivity.

35. 1. atoms positive charge is concentrated in the nucleus
2. proton (p)- (+) charge ; electron (e)- (-) charge
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)

36. Model pictures a very empty
atom.
Radius of atom is 150,000
times the radius of nucleus.
Nucleus contains most of the
mass.
Electrons occupy most of the
volume.

37. Billiard Ball Model Plum Pudding Model
Nuclear Model

38. Eugene Goldstein
(1850 –1930)

39. • The mass of this particle almost the same
as the mass of the H atom
• The charge is equal in magnitude (but
opposite in sign to that of the electron)
• Named the particle proton
• Responsible for the total + charge of the
nucleus- nuclear charge

40. • James Chadwick
• (1891 –1974)
-identified the neutron by bombarding
a thin Be sheet with α particles
-emission of very high energy
radiation similar to ϒ rays
-consisted of electrically NEUTRAL
particles with a slightly greater mass
than that of a proton.

41. Neutronmass p = mass n = 1840 x mass e-

42. (Electrons, protons and neutrons make their
presence felt!)