Transcript Chapter 5 Early Atomic Theory and Structure

Chapter 5
Early Atomic Theory and
Structure
The History of
the Atom…
Objectives
• History of Atomic Theory (5.1-5.5, 5.7)
• Subatomic Particles (5.5, 5.8)
• Atomic Numbers (5.9)
• Isotopes (5.10)
• Atomic Mass (5.11)
Democritus of Abdera
• ~460 BC to 370
BC
• World made of
empty space and
tiny particles
called “atoms”
• Student of
Leucippus
Democritus of Abdera
1) All matter is composed of atoms, which
are bits of matter too small to be seen.
These atoms CANNOT be further split
into smaller portions
2) There is a void, which is empty space
between atoms
3) Atoms are completely solid
4) Atoms are homogenous, with no
internal structure
5) Atoms differ in size, shape and weight
Aristotle
• Opposed ideas of
Democritus
• Empedoclean
theory
– 4 elements
• Earth, air, fire, water
• Ideas dominate into
17th century…
Atomism in Antiquity
• Church spoke
against atoms
–Did not support
God creating
earth
Atomism in the Middle Ages
• Artistotle’s works
rediscovered (1200s)
• Catholic Church
– Atomic thinking =
Godlessness
• De Rerum Natura
rediscovered in 1417
– Prime source for
ideas of Leucippus
and Democritus
Atomism in the Renaissance
• Dominated by
Alchemists
– Mystics, fakes
– Turning cheap metal
into gold
• Discovery of many
elements
• Preparation of
mineral acids
Robert Boyle (1627-1691)
• Matter is divided into
little particles of
several sizes
(corpuscles)
• First to perform truly
quantitative
experiments
– Pressure and volume
of air
Antoine Laurent Lavoisier
Father of Chemistry
• 1743-1794
• Matter can be
changed but never
created or
destroyed
• Law of
Conservation of
Mass
Antoine Laurent Lavoisier
Father of Chemistry
"It took them
only an instant to
cut off that head,
and a hundred
years may not
produce another
like it."
Amadeo Avogadro
•(1776-1856)
•Equal volumes
of gases, under
the same
conditions, have
the same number
of molecules
John Dalton
•(1766-1844)
•Englishman
•School teacher
•Developed
atomic theory
John Dalton
1. All matter is composed
of atoms
2. Atoms of the same
element are identical
3. Atoms cannot be
subdivided, created or
destroyed
John Dalton
4. Atoms of different
elements combine in
small whole numbers
5. In chemical reactions,
atoms are combined,
separated or
rearranged
John Dalton
Law of Multiple Proportions
When two elements form a series of
compounds, the ratios of the
masses of the second element
that combine with 1 gram of the
first element can always be
reduced to small whole numbers
CO, CO2, CO3, etc….
J. J. Thomson
•1856-1940
•Showed
experimentally the
existence of the
electron
J. J. Thomson
•Cathode Tube
Experiment
J. J. Thomson
Robert A. Millikan
•Determined
charge of an
electron
•Negative
Ernest Rutherford
•1871-1937
•Defined
radioactivity
•Named alpha
and beta particles
Ernest Rutherford
Ernest Rutherford
The Modern Day Atom
• Nucleus:
– Positively
charged protons
– Neutral
neutrons
• Orbiting
Nucleus:
– Negatively
charged
electrons
Atomic Numbers (Z)
• Equal to number of protons in the nucleus
• NEVER CHANGES
Mass Number (A)
• Sum of protons and neutrons in the nucleus
Isotopes of the Elements
• Same atomic number but different atomic
masses
• Different number of neutrons
Ions of the Elements
•Same number of protons and
neutrons
•Has lost or gained electrons
–Contains charge…
Atomic Mass
• Measured in atomic mass units
– Equal to exactly 1/12 mass of a carbon-12 atom
• Average relative mass of the isotopes of that
element compared to the atomic mass of
carbon-12
• Average atomic mass (seen on periodic
table)
– Atomic mass of each isotope x fraction present
– Add all….
– See pg 95