Download Ch. 4.1 Notes - BAschools.org

Ch. 4.1
Atomic Structure
(History)
Chapter 4.1
An Atomic Model of Matter
•The Greek Model
• Dalton’s model
• Thomson’s model
•Rutherford’s model
•Bohr’s model
• Modern model
How Elements Are Formed Clip
•
•
•
•
Ancient Philosophy
Who: Aristotle, Democritus
When: More than 2000 years ago (400 B.C.)
Where: Greece
What: Aristotle believed in 4 elements: Earth,
Air, Fire, and Water. Democritus believed
that matter was made of small particles he
named “atomos”. Two prevailing theories.
• Why: Aristotle and Democritus used
observation and inference (indirect evidence)
to explain the existence of everything.
Democritus
Aristotle
Alchemists
•
•
•
•
Who: European Scientists
When: 800 – 900 years ago
Where: Europe
What: Their work developed into what is now
modern chemistry.
• Why: Trying to change ordinary materials
into gold.
Particle Theory
•
•
•
•
Who: John Dalton
When: 1803
Where: England
What: Described atoms as tiny particles that
could not be divided. Thought each element
was made of its own kind of atom.
• Why: Building on the ideas of Democritus in
ancient Greece.
Particle Theory
•
•
•
•
4 Parts of Dalton’s Theory
All elements are composed of
indivisible particles (atoms).
Atoms of the same element are
exactly alike.
Atoms of different elements are
different.
Compounds are formed by
John Dalton
joining atoms of two or more
elements.
Discovery of Electrons
•
•
•
•
Who: J. J. Thomson
When: 1897
Where: England
What: Thomson discovered that electrons
were smaller particles of an atom and were
negatively charged.
• Why: Thomson knew atoms were neutrally
charged, but couldn’t find the positive
particle. Therefore, the atom must be
composed mostly of positively charged
material. (Plum Pudding Model).
Atomic Structure I
•
•
•
•
Who: Ernest Rutherford
When: 1908
Where: England
What: Conducted an experiment to isolate
the positive particles in an atom. Decided
that the atoms were mostly empty space, but
had a dense central core (nucleus).
• Why: He knew that atoms had positive and
negative particles, so the nucleus must be
positively charged.
The Gold Foil Experiment Clip
Ernest
Rutherford
Atomic Structure II
•
•
•
•
Who: Niels Bohr
When: 1913
Where: England
What: Proposed that electrons traveled in
fixed orbits around the nucleus. Scientists
still use the Bohr model to show the number
of electrons in each orbit around the nucleus.
• Why: Bohr was trying to show why the
negative electrons were not sucked into the
nucleus of the atom.
Atomic Structure III
•
•
•
•
Who: James Chadwick
When: 1935
Where: England
What: Discovered the neutral particle in the
center of the atom (neutron).
• Why: Chadwick was trying to figure out the
discrepancy of atomic mass not being equal
to the number of protons plus electrons. He
theorized there must be a massive particle
that had no charge and was therefore hard to
find.
Electron Cloud Model
• Electrons travel around the nucleus in
random orbits (no definite paths).
• Scientists cannot predict where they will be
at any given moment.
• Electrons travel so fast, they appear to form
a “cloud” around the nucleus.
• The small, positively charged nucleus is
surrounded by a large space called the
electron cloud.
The Modern Model
• Electrons are behaving more
like waves than planets and
they vibrate back and forth.
• They are like bees around a
hive.
• History Timeline of the Atom
Building blocks of
molecules
• Atoms are the smallest part of
an element that acts like that
element
• Atoms are composed of 3
smaller particles: Protons,
electrons and neutrons.
The Model of the Atom Through Time
Modern
The Atom
• Nucleus
center of atom.
contains neutrons
contains protons
• Neutrons
0
neutral charge N
1.67 x 10-27 mass in the nucleus
Protons | Electrons
Negative charge e-31 Mass
9.11
x
10
1.67 x 10 -27 Mass
Found outside
Found in the nucleus
nucleus in energy
Proton Charge (+1) levels /shells in a
specific orbital
electron
charge (-1)
Positive charge P+
Electron Shells
• Electrons (e-) can be
found in 1 of 4 shells
st
• 1 shell holds 2 e
• 2nd shell holds 8 erd
• 3 shell holds 18 e
th
• 4 shell holds 32 e
Orbitals
• Electrons can be found in
1 of 4 orbitals in the shells
( s, p, d, or f orbitals )
• S orbital
lowest level
2 electrons
sphere shape
Orbitals
P orbital
x
y
Holds 6 electrons
dumbbell shape
z
D orbital
Holds 10 electrons
F orbital
Holds 14 electrons
F orbital  highest energy level
Valence Electrons
• The last shell electrons are
found in what is called the
valence shell
• These electrons are then
called the valence electrons
and they are what determine
if the atom will bond with
anything else or not.
The Atom
• All atoms are neutral so …
• Protons which are positive
must equal electrons which
are negative
(they cancel each other out)
• WKRP Atom Explanation