Download The Atom

Atomic Theory and
Structure
The Theory of the Atom
Democritus
• ___________, a Greek teacher in
the 4th Century B.C., first
suggested the idea of the atom.
• All matter is composed of tiny,
indivisible particles called
_________
atoms
_______
•
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John Dalton
1803, ____________
studied
experiments and concluded that the
properties of matter could be
atoms
explained in terms of _____.
 In
 Dalton’s
1.
2.
_____________
Atomic Theory had 4
points
Each ________
element is composed of
extremely small particles called
atoms (which are indivisible).
All atoms of a given element are
identical but they differ from
_______,
those of any other element.
Atomic Theory Continued…
3. Atoms are neither ________
created
nor destroyed
________ in any chemical
reaction.
compound always has
4. A given _________
the same relative numbers and
kinds of atoms.
Dalton’s Model of the Atom
He believed the atom was a
solid sphere
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The Atom
Is composed of an
ELEMENT
__________ is an
atom.
 The atom is made up
SUBATOMIC
of three ___________
PROTONS
particles: ________,
NUETRONS
___________
and
ELECTRONS
__________

 Michael
Faraday
1893
Atoms
contain particles that
electrical charge
have an __________
Electron
 Discovered in 1897 by
JJ Thomson
__________
negative charge
 Has a _________
Thomson also thought in
addition to the negatively
charged electrons, there must
be something with a
positive
__________
charge because
the overall charge of the
neutral
atom is ___________
Plum
Pudding
Model
Ernest Rutherford
 Performed Gold Foil
1909
Experiment in ______.
alpha particles (very
 He shot _______
small, dense, fast and positively
charged particles) at a thin layer
of gold foil.
Gold foil
Alpha
particles
source
Detector screen
Alpha particles
Because of Thomson’s Atom
But, what he found was this…
Most of the alpha particles went
straight through but a tiny amount
were deflected
In the atom there was something
dense enough to deflect the alpha
nucleus
particles = ________
Like this…
Importance of Rutherford’s
Experiment
1. Showed most of the atom is
space
made up of empty __________
 2. Proved the atom had a small,
dense area in its center known now
nucleus
as the _____________
positive
 3. The nucleus has a _________
protons
charge (must have __________
in it)

Rutherford’s Atom
Other
important
discoveries……
Neutron
 Discovered
in 1932 by James
____________
Chadwick
neutral
 Has no charge (i.e. It is ______)
Proton
1886 by E.
 Discovered in ______
Goldstein
positive charge
 Has a ________
Bohr Model
Modern Atomic Structure
 The atom is made up of 2 parts/sections
nucleus --- (in the center of
(1) The _________
the atom; contains protons and neutrons)
electron cloud --- (surrounds
(2) The _____________
the nucleus)
Nucleus (protons and neutrons)
Electrons cloud (electrons)

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The Atom
The
smallest particle of an
element is an atom.
________
 The atom is made up of
subatomic particles:
three _________
protons _________,
neutrons and
_______,
electrons
_______
Particle Charge Location Mass
(g)
Proton Positive Nucleus
+
(P )
Mass
(amu)
-24
1.673 x 10
-24
Neutron Neutral Nucleus 1.675 X 10
(N°)
(No
charge)
Electron Negative Around
(E )
Nucleus
-28
9.109 x 10
1
1
1
1837
Protons
Overall Charge
 The
overall charge of an atom is
0
____(neutral)
 So, the number of protons must
equal the number of electrons
_______
 So, the atomic number also tells
us the number of
electrons
_______________in
an atom
Mass Number
The
mass of an atom
AMU’s
Measured in ________
Equal to the total number of
__________
and
protons
neutrons
__________
How to determine……..
 1)
The number of protons = Look
atomic number
at ______________
 2) The number of electrons = Look
atomic number
at ______________(number
of
protons = number of electrons)
 3) The number of neutrons =
Mass
number – atomic number
___________
Practice Problems
1) Find the # of e-, p+ and n0 for sodium.
(mass # = 23)
2) Find the # of e-, p+ and n0 for uranium.
(mass # = 238)
3) What is the atomic # and mass # for the
following atom?
# e- = 15; # n0 = 16
When
Ions
an atom loses or gains
one or more ________,
electrons it
acquires a net electrical charge
ion
and is called an ____.
2
types of ions:
1)
Anion
2) Cation
Anions and Cations
Anion
 ____________:
An ion that has
more electrons than protons has a
___________
negative charge.
**(Gained Electrons)**
Cation
 ____________:An
ion that has
fewer electrons that protons has a
positive
_____________
charge.
**(Lost Electrons)**
Determining the Charge of an Ion
#
of protons - # of electrons
Ion Notation
Practice Problems
1) A neutral magnesium atom (atomic
number 12) has 12 protons and 12
electrons. If the atom loses 2 electrons,
what is the charge of the resulting ion?
2) How many electrons would be found
in the ion O2-?
3) If an ion has 28 protons and 26
electrons, what is its charge? What is
its symbol (including charge)?
Isotopes
 An
isotope refers to atoms that
protons but
have the same # of ______,
neutrons
they have a different # of _______.
 Because of this, they have different
____
mass #’s (or simply, different
______.)
masses
Exm: (1) Carbon-12 & Carbon-13
(2) Chlorine-35 & Chlorine-37
(The # shown after the name is the mass #.)
 For
each example, the elements
have identical ______
atomic #’s, but
mass #’s
different _____
Isotopes cont…
 In
nature, elements are found as
mixture
a _______________
of all their
isotopes
 The isotopes are found in the
percentage
same __________________
More Practice Problems
+
0
1) Find the # e , p and n for Xe131.
2) Find the #
e,
+
p
and
0
n
63
for 29Cu
3) Write a shorthand way to
represent the following isotope:
0
+
#e =1
#n =0 #p =1
Atomic Mass
The
atomic masses listed in the
Periodic Table are a
weighted average
“_____________”
of all the
isotopes of the element.
Practice Problems
(1) Mrs. Smith’s geometry semester grades are
calculated using a weighted average of three
category scores:
Tests/Quizzes= 30% of your grade
Homework/Participation=60% of your grade
Semester Exam= 10% of your grade
 If a student had the following scores, what would
they receive for the semester?
Tests/Quizzes= 80 (B-)
Homework/Participation= 60 (D-)
Semester Exam=65 (D)
Step (1): Multiply each score by the % that
it is weighted.
Step (2): Add these products up, and that is
the weighted average! +
A “normal average” would be calculated
by simply adding the raw scores together
and dividing by 3…
80 + 60 + 65 = 205 ÷ 3 = 68.3 = D
(2) In chemistry, chlorine has 2 isotopes:
Cl-35 (75.8% abundance)
Cl-37 (24.23 % abundance)
What is the weighted average atomic mass
of chlorine?
+
(3) Oxygen has 3 isotopes:
O-16 (99.76%) O-17 (0.037%)
O-18 (0.2%)
Estimate oxygen’s average atomic mass.