Download THE ATOM

The History of the Atom…….
• Democritus was the
first to theorize that all
matter was composed
of atoms!
• Democritus’ ideas
were crushed by a
contemporary,
named……….
………………Aristotle!!!!
• Aristotle asked
Democritus three
questions:
• If we are made of atoms,
what holds us together?
• Why can’t we see these
atoms?
• Why don’t we fall down
like a bag of marbles?
By weighing the materials before and after...
• Antoine Lavoisier came up
with……..
• The law of Conservation of Mass
• This
states:
- Matter cannot be created or
destroyed in a chemical reaction,
simply converted from one form into
another
• John Dalton ends up using this point
in his theory of an atom!
Joseph Proust…
• Came up with the Law of
Definite Proportions
• He had examined copper
carbonate decomposition and no
matter the amount he started
with, whenever it decomposed it
would yield 5.3 parts copper,
4.0 parts oxygen and 1.0 parts
carbon
• John Dalton ends up using this
point in his theory of an atom!
Law of Definite Proportions- Elements that make up compounds
(like water H2O) are ALWAYS in the same proportion by matter.
H2O
It took almost 2000 years before the idea of the atom came back!
• John Dalton (school teacher) brought Democritus’ idea back!
All matter is made of atoms!
• His points were:
– All matter is made up of atoms (from Democritus)
– Atoms are indestructible and can’t be divided into smaller
particles. (not true)
– Atoms of one element are exactly alike, but they are different from
other elements. (not exactly true)
– Chemical reactions rearrange atoms- no atoms form or disappear.
(from Lavoisier)
– Molecules and compounds always consist of a certain combination
of atoms that never varies. (H2O) (from Proust)
• John Dalton’s theory has been modified as we learned new
information……..
Dalton thought Atoms are solid and
indestructible, THEY ARE NOT.
Are these atoms or am I
Losing my marbles?
• Atoms contain different
parts…….
• However, scientists did
not know this until parts
of the atom were
discovered…..
• What part of the atom do
you think was discovered
first…..?
THE ELECTRON………..
• See Thomson’s
experiment on page 102 of
the Physical Science book.
• Scientists knew that
matter was not negatively
charged, so atoms couldn’t
be either…. There had to
be positively charged
particles too!
Protons were discovered next
and then were followed by
Neutrons.
see pgs 102-109 in the Physical Science book.
Thomson’s Atom Model
In Thomson’s "Plum Pudding Model" each atom was a
sphere filled with a positively charged fluid. The fluid was
called the "pudding." Scattered in this fluid were
electrons known as the "plums."
QuickTimeª and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Rutherford’s “Football Analogy”
Football Stadium
TO REVIEW….
“I, Democritus, came up with the “atom” idea”
“I, Dalton, proposed solid indivisible balls like marbles”
“I, Thompson, said an atom is positive, with negative
Electrons…. Like cookie dough or plum pudding”
“I, Rutherford, came up with the idea the nucleus is
Positive and the atom is mainly empty space”
Bohr' s Atom Model
Electron Cloud Model
MODERN ATOMIC THEORY
Subatomic Particles
•3 main ones (there are others, but that’s for physics..)
–Electrons
–Protons
–Neutrons
MODERN ATOMIC THEORY
• Nucleus has protons (+) and neutrons (neutral)
• Electrons (-) move around nucleus
• Nucleus is very TINY and takes up the least amount of
space in an atom.
• Most of an atom is EMPTY SPACE!
QuickTimeª and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
• 1 drop of water = 6.5 x 1023 atoms
(6.5 sextillion or 650000000000000000000000)
Name of
Subatomic
Particle
Charge of
Particle
Relative Mass
(compared to
other subatomic
particles)
Location in Atom
ATOMIC NUMBER= # of protons in the nucleus
This number NEVER CHANGES and so it can be used to
identify the element !!!
PROTONS give an element its identity
for example: If an atom has 6 P….it’s CARBON
7 P…….N
1 P…….?
53 P……?
IF the atom is NEUTRAL this is also the # of electrons
outside the nucleus.
MASS NUMBER
• Mass # = number of protons + number of neutrons
in the nucleus.
• ALL the mass of an atom comes from the __________
and_____________ in the ____________ of the atom.
• measured in atomic mass units (amu)
•
Chlorine
Mass # of chlorine: 35 amu
Example:
Protons= ? (from atomic number)
Neutrons= ? (mass # - atomic #)
How to read the periodic table….
197
79Au
# P = 79
Which is atomic #?
What does that tell us?
Which is mass #?
What does that tell us?
# N = (197-79) = 118
# e- = 79
Charge….d atom!
If an atom has a charge… which subatomic particle
would have to have changed in number?
Is it the # of protons, # of electrons or # of neutrons?
ATOMIC CHARGES
• Ion = an atom that loses or gains one or
more electrons
2 types of ions are:
Cations –positively charged ions
-loses one or more electrons
Anions –negatively charged ions
-gains one or more electrons
THIS IS AN ION ( +1 CHARGE)
23
+1
Na
11
# P = 11
# N = (23-11)
= 12
#e- = 10
How many electrons would sodium normally have?
Did sodium lose or gain an electron?
How many electrons did sodium lose or gain?
Is this charged atom a cation or an anion?
ISOTOPES
Thomson discovered that neon consisted of atoms of 2 different
masses. The number of protons identifies the element and electrons
have virtually no mass…. So which subatomic particle would be
different and change the mass?
• Isotopes are the same element (same # of protons)
• They are chemically alike
• They have different atomic masses. (because they
have different # of neutrons )
• Example:Lithium-6, and Lithium-7 are isotopes
• Lithium - 6 has a mass of 6amu (3 protons + 3 neutrons)
• Lithium - 7 has a mass of 7amu (3 protons + 4 neutrons)
• Why doesn’t the # of protons change? Because the # of protons
gives it it’s identity! Lithium!
Example of an isotope
– 11H, 21H, 31H
– All are Hydrogen
because they have 1
proton.
• Isotope #P
#N
1 H
1
0
1
mass of 1 = (1 P + 0 N)
2
1H
1
1
mass of 2 = (1 P + 1 N)
3
1H
1
2
mass of 3 = (1 P + 2 N)