Download Atom


History
Empedocles(440 B.C)




Democritus (400 B.C.)



Everything is composed of 4 elements
and controlled by two forces
Earth, Fire, Air, Water
Love and Strife
named the most basic particle
atom- means “indivisible
Aristotle (340 B.C.)


didn’t believe in atoms
thought matter was continuous

Problem: No Evidence

http://cwx.prenhall.com/petrucci/medialib/media_portfolio/02.html
History
 by


1700s, all chemists agreed:
on the existence of atoms
that atoms combined to make
compounds
 Still
did not agree on whether
elements combined in the same ratio
when making a compound
Law of Conservation of Mass
 Antonine
Lavoisier (1782)
 mass is neither created or destroyed
during regular chemical or physical
changes
 Mass of Reactants = Mass of Products
Law of Definite Proportions
 Joseph
Proust (1799)
 any amount of a compound contains
the same element in the same
proportions by mass
No matter
where the
copper
carbonate is
used, it still
has the same
composition
Law of Multiple Proportions
applies when 2 or more elements combine
to make more than one type of compound
 the mass ratios of the second element
simplify to small whole numbers

Law of Multiple Proportions
John Dalton
 1803
 Father
of “Modern Atomic Theory”
 Started Teaching at age 12
 Believed the atom was a solid sphere
of one element
 Studied other scientists findings
Dalton’s Atomic Theory
1.
All matter is made up of atoms.
Atoms are the smallest fundamental
units of matter.
Dalton’s Atomic Theory
TRUE
1.
All matter is made up of
atoms. Atoms are the smallest
fundamental units of matter.
Dalton’s Atomic Theory
TRUE
1.
2.
All matter is made up of
atoms. Atoms are the smallest
fundamental units of matter.
All elements consist of atoms
which are indivisible &
indestructible.
Dalton’s Atomic Theory
TRUE
1.
FALSE
2.
Nuclear reactions
All matter is made up of
atoms. Atoms are the smallest
fundamental units of matter.
All elements consist of atoms
which are indivisible &
indestructible.
Dalton’s Atomic Theory
TRUE
1.
FALSE
2.
Nuclear reactions
All matter is made up of atoms. Atoms are the
smallest fundamental units of matter.
All elements consist of atoms which are indivisible &
indestructible.
3.
All atoms of the same element
are identical in size, shape &
mass.
Dalton’s Atomic Theory
TRUE
1.
FALSE
2.
Nuclear reactions
FALSE
Isotopes
All matter is made up of atoms. Atoms are the
smallest fundamental units of matter.
All elements consist of atoms which are indivisible &
indestructible.
3.
All atoms of the same element
are identical in size, shape &
mass.
Dalton’s Atomic Theory
TRUE
1.
FALSE
Nuclear reactions
2.
indivisible & indestructible.
FALSE
Isotopes
TRUE
All matter is made up of atoms. Atoms
are the smallest fundamental units of
matter.
All elements consist of atoms which are
3.
All atoms of the same element are
identical in size, shape & mass.
4.
Atoms of different
elements are different in
size, shape, & mass.
Dalton’s Atomic Theory
TRUE
FALSE
1.
2.
All matter is made up of atoms. Atoms are the smallest
fundamental units of matter.
All elements consist of atoms which are indivisible &
indestructible.
FALSE
TRUE
TRUE
3.
All atoms of the same element are identical in size, shape &
.
mass
4.
Atoms of different elements are different
in size, shape, & mass.
5.
In a chemical reaction, atoms are
rearranged, never created nor
destroyed & they combine in whole
number ratios.
Dalton’s Atomic Model
Dalton’s Atomic Theory
1.
2.
3.
4.
5.
All mass is made of atoms
Atoms of same element have the same
size, mass, and properties
Atoms can’t be subdivided, created or
destroyed
Atoms of different elements combine in
whole number ratios to make compounds
In chemical reactions, atoms are
combined, separated, and rearranged.
Modern Atomic Theory

Some parts of Dalton’s theory were wrong:



atoms are divisible into smaller particles
(subatomic particles)
atoms of the same element can have different
masses (isotopes)
Most important parts of atomic theory:



all matter is made of atoms
atoms of different elements have different
properties
Atoms of different element combine in whole
number ratios to make compounds
Other contributions

Faraday


Helped to provide evidence of Dalton’s work
Millikan

His oil drop experiment determined the charge
of an electron
History
JJ Thomson (1897) (Plum Pudding Model)
 Discovers the Electron
 Cathode Ray Tube Experiment
 (Goldstein in 1906) Positively Charged
Particles
JJ Thomson
4 Ideas of Electric
Charge
 Atoms are generally
neutral
 Electric charges are
properties of
particles of matter
 Exist in a single unit
 Electric charges
cancel out
Radioactivity
Curie and Becquerel
 Becquerel used a uranium and found
that it emitted radiation from it
 Marie Curie further investigated his
work and classified the radiation into
3 forms



Alpha Rays - Positively Charged
Beta Rays - Negatively Charged
Gamma Rays – No Charge
History
Ernest Rutherford (1910)
 Kiwi
 Gold Foil Experiment
Discovery of Nucleus


Rutherford discovered
the nucleus by
shooting alpha
particles (have positive
charge) at a very thin
piece of gold foil
he predicted that the
particles would go
right through the foil
at some small angle
The Results
Most positive charges past through because
the atom is mostly empty space.
 Some of the positive charges deflected
because the atom contains some positive
charge.
 Some of positive charges deflected straight
back because there is a concentrated area
of positive charge (nucleus).

Discovery of Nucleus
 some
particles (1/8000) bounced back
from the foil
 this meant there must be a “powerful
force” in the foil to hit particle back
Predicted Results
Actual Results
Discovery of Nucleus
Characteristics of
“Powerful Force”:
1. dense- since it was strong
enough to deflect particle
2. small- only 1/8000 hit the
force dead on and bounced
back
3. positively charged- since
there was a repulsion
between force and alpha
particles
How Powerful
 “It
was if you shot 15 inch shell at a
piece of tissue paper and it bounced
back at you”
• Ernest Rutherford
 Rutherford’s
experiment explained
that the neutral charge of most
atoms…
Rutherford’s Atomic Model
_
_
_
+++
_
++++
+++
_
Nucleus- Contains Protons
_
Electrons surround nucleus
Lots of empty space
_
_
What about Mass
…
it didn’t account for the mass ratio
of Helium to Hydrogen to be 4:1

If Rutherford was correct the mass of
Helium to Hydrogen should be 2:1
James Chadwick
 1891-1972
 Proved
the existence of Neutrons
 Electrically Neutral Particles having a
mass slightly greater than that of
protons
…And

Why? Why? Why?
Don't the electrons
get pulled to the
center where the
protons are?
_
_ +++ _
_ ++++
_
_ +++
_
Neils Bohr
1913
 Positively Charged
Nucleus
surrounded by
electrons in orbit
 Primitive Model

History of the Atom
Structure of Atom

Nucleus:



contains protons
and neutrons
takes up very little
space
Electron Shell


contains electrons
takes up most of
space
Subatomic Particles
 includes



all particles inside atom
proton
electron
neutron
 charge
on protons and electrons are
equal but opposite
 to make an atom neutral, need equal
numbers of protons and electrons
Subatomic Particles
number of protons identifies the atom as a
certain element
 protons and neutrons are about same size
 electrons are much smaller
 nuclear force- when particles in the nucleus
get very close, they have a strong attraction




proton + proton
proton + neutron
neutron + neutron
Properties of Subatomic
Particles
Atomic
Particle
Symbol
Electric
Charge
Electron
e-
1-
Proton
p+
1+
Neutron
n0
0
Approx.
Mass
(amu)
Actual
Mass
1/1840
9.11 x 10-28
1
1.67 x 10-24
1
1.67 x 10-24
Atoms
Atom: smallest particle of
an element that has all
of the elements
characteristics;
composed of electrons,
protons, & neutrons



17

Cl

35.45
17 = Atomic Number &
# of Protons in an atom
Cl = Atomic Symbol
35.453 = Atomic Mass
(or Mass Number) =
Protons+Neutrons
** A neutral atom
always has the same #
of protons & electrons
** Ion: an atom with a
charge; due to the loss
or gain of electrons
Isotopes
Isotope: When atoms of
the same element have
different mass
numbers; due to
different neutron #’s
 Ex: C12 & C14 - C12 has 6
neutrons and C14 has 8
neutrons
 The Atomic Mass of an
element is the average
mass of all known
isotopes of that
element
 Some isotopes are
radioactive