Transcript history of atom

Atomic structure
chp 3 sec 2
The Greek model, Dalton’s
Model, Thomson’s model,
Rutherford’s model, Bohr’s
Model and the Modern Model
The Greek Model
•Democritus said matter could
not be divided into smaller and
smaller pieces for ever .
•He proposed the atoms
• and called it Atomos
•which means not divisible.
•He was an Atomist.
Atomist used Indirect Evidence
•Greek philosophers had only
indirect evidence in which to study
from. There were no microscopes,
•This is evidence you get without
seeing or touching
Modern Atomic Theory (Dalton)
 All matter is composed of atoms
 Atoms cannot be subdivided, created, or
destroyed in ordinary chemical reactions.
However, these changes CAN occur in
nuclear reactions!
Atoms of an element have a characteristic
average mass which is unique to that
element.
Atoms of any one element differ in
properties from atoms of another element
Thomson’s Atomic Model
Thomson believed that there were negative
particles like plums embedded in a positively
charged “pudding,” thus it was called the “plum
pudding” model.
Conclusions from the
Study of the Negative particle
Atoms are neutral, so there must be
positive particles in the atom to balance the
negative charged particles
 The negative particles are called
electrons and they have so little mass that
atoms must contain other particles that
account for most of the mass (the positive
pudding)
Rutherford’s Gold Foil Experiment
 Alpha () particles are helium nuclei
 Particles were fired at a thin sheet of gold foil
 Particle hits on the detecting screen (film) are
recorded
Rutherford’s Findings
 Most of the particles passed right through
 A few particles were deflected
 VERY FEW were greatly deflected
“Like howitzer shells bouncing off
of tissue paper!”
Conclusions:
 The nucleus is small
 The nucleus is dense
 The nucleus is positively charged
Bohr’s Model
•Bohr stated that electrons
orbited around the
nucleus like planets
around the sun and each
orbit was a different
energy level.
The Modern Model
•Electrons are behaving more
like waves than planets and
they vibrate back and forth.
•They are like bees around a
hive.
Electron shell configuration
The number of the shell denotes how many can fit
Atomic Particles
Atomic number (Z)
• Protons &
• electrons
Symbol
• Element name
Atomic Mass (A)
amu
•Amu= SI unit for atomic mass
Protons +
Neutrons
Atomic Number
Atomic number (Z) of an element
is the number of protons in the
nucleus of each atom of that
element.
Element
# of protons
Atomic # (Z)
6
6
Phosphorus
15
15
Gold
79
79
Carbon
Mass Number
Mass number is the number of protons and
neutrons in the nucleus of an isotope.
Mass # = p+ + n0
18
Arsenic
Phosphorus
8
75
16
8
18
33
75
15
31
Ions
•Ions gain/lose electrons to
become happy and by
using the oxidation
number you can
determine how many.
Isotopes
Isotopes are atoms that
gain/lose neutrons and
their mass changes.
The mass on the
periodic table is the
average of all isotopes
Atomic Masses
Atomic mass is the average of all the
naturally occurring isotopes of that element.
Isotope
Symbol
Composition of
the nucleus
% in nature
Carbon-12
12C
6 protons
6 neutrons
98.89%
Carbon-13
13C
6 protons
7 neutrons
1.11%
Carbon-14
14C
6 protons
8 neutrons
<0.01%
Carbon = 12.011