Download 4.1 Introduction to Atoms

Atoms!!!!
Chapters 4.1, 5.1, 4.2, 4.3, 4.4, 4.5
What are Atoms?
Atoms are very tiny particles that form
the building blocks for all matter
Just What Size Is an Atom?
Let’s do a little exercise!!
What you’ll need
• A strip of paper
• A pair of scissors
DON’T DO THIS YET!
Here is what to do …
• Take your strip of paper and cut it into equal halves
• Cut one of the remaining pieces of paper into equal
halves
• And so on …
Just What Size Is an Atom?
Cut 1
Hand
Pocket
14 cm
Just What Size Is an Atom?
Cut 2
Finger
Ear
7.0 cm
Just What Size Is an Atom?
Cut 3
Watch
Mushroom
Eye
3.5 cm
Just What Size Is an Atom?
Cut 4
Keyboard
Key
Ring
Insect
1.75 cm
Just What Size Is an Atom?
Cut 5
Keep going …
atoms are much smaller!
0.88 cm
Just What Size Is an Atom?
Cut 6
Tiny seeds on top
of a Whopper bun
0.44 cm
Just What Size Is an Atom?
Cut 7
Keep going …
atoms are still much smaller!
0.22 cm
Just What Size Is an Atom?
Cut 8
Thread
1.0 mm
Just What Size Is an Atom?
Cut 9
It’s too difficult to keep cutting!
Let’s just pretend from now on
0.5 mm
Just What Size Is an Atom?
Cut 10
The size of one
tiny light (pixel) on
a computer screen
0.25 mm
Just What Size Is an Atom?
Cut 11
Wow, I didn’t think anything
was this small!
0.125 mm
Just What Size Is an Atom?
Cut 12
A piece
of hair
0.06 mm
Just What Size Is an Atom?
Cut 13
Our meter has disappeared!
???
0.03 mm
Just What Size Is an Atom?
Cut 14
The width of paper
0.015 mm
Just What Size Is an Atom?
Cut 15
We’re not done yet
keep cutting!
0.007 mm
Just What Size Is an Atom?
Cut 16
Bacteria
0.003 mm
Just What Size Is an Atom?
Cut 17
We’re not done yet
keep cutting!
0.0015 mm
Just What Size Is an Atom?
Cut 18
Water filter
1.0 micron
Just What Size Is an Atom?
Cut 19
We’re not done yet
keep cutting!
0.5 micron
Just What Size Is an Atom?
Cut 20
Tiny wires inside a
computer chip
0.25 micron
Just What Size Is an Atom?
Cut 21
We’re not done yet
keep cutting!
0.13 micron
Just What Size Is an Atom?
Cut 22
Virus
0.07 micron
Just What Size Is an Atom?
Cut 23
We’re not done yet
keep cutting!
0.03 micron
Just What Size Is an Atom?
Cut 24
We’re not done yet
keep cutting!
0.015 micron
Just What Size Is an Atom?
Cut 25
We’re not done yet
keep cutting!
0.008 micron
Just What Size Is an Atom?
Cut 26
Almost there
5 Cuts left
0.004 micron
Just What Size Is an Atom?
Cut 27
Almost there
4 Cuts left
0.002 micron
Just What Size Is an Atom?
Cut 28
Almost there
3 Cuts left
0.001 micron
Just What Size Is an Atom?
Cut 29
Almost there
2 Cuts left
0.0005 micron
Just What Size Is an Atom?
Cut 30
Almost there
1 Cut left
0.00025 micron
Just What Size Is an Atom?
Cut 31
H
Ca
He
Atoms !!!
Cl
C
O
Na
N
0.00013 micron
Atom Facts
• A sheet of paper is about 10,000 atoms
thick
• There are about
2,000,000,000,000,000,000,000 (that’s 2
thousand billion billion) oxygen atoms in
a small drop of water. There are twice
that many hydrogen atoms.
Objectives
1. I will know where metals, nonmetals and
inert gases are found on the periodic
table.
2. I will know that each element has a
specific number of protons in the
nucleus and that this is the same as the
atomic number.
Objectives
3. I will know what an isotope is and that
isotopes of an element have a different but
specific number of neutrons in the nucleus.
4. I will know that substances can be classified
(sorted) by their properties such as melting
points, densities, hardness, thermal
conductivity (how well heat travels through
the substance) and electrical conductivity
(how well electricity travels through the
material).
Chapter 4.1
Introduction to Atoms
Development of the Atomic
Theory
• The development of
the modern atomic
theory shows how a
theory is based on
experimental
evidence, but is
modified, as more
evidence is collected.
Development of the Atomic
Theory
• The 1st people to think about the
nature of matter were the Greeks in
430 B.C.
– Democritus proposed that the idea of
matter is formed of small pieces that
could not be cut into smaller parts.
– He used the term atomoV (atomos)
which means “uncuttable” for the small
pieces.
Democritus
• He also thought that sweet
tasting objects have
smooth atoms, sour tasting
objects have sharp atoms
• In modern terms, an atom
is the smallest particle of
an element.
“Nothing exists but
atoms and empty
space, everything
else is opinion ---”
Atomic Theory Continued…
• Atomic theory grew as a series of models that
developed from experimental evidence. As
more evidence was collected, the theory and
models were revised.
• Many scientists were involved in the
development of the atomic theory.
– John Dalton
– J.J. Thomson
– Ernest Rutherford
– Niels Bohr
John Dalton
• John Dalton (17661844)
• British School Teacher
• First to do research on
color blindness (he was
color blind)
• Did independent
research in his
laboratory
John Dalton
• John Dalton was an English chemist and
inferred that atoms had certain
characteristics.
• Dalton’s ideas included:
– All elements are composed of atoms that cannot
be divided.
– All atoms of the same element are exactly alike
and have the same mass.
– An atom of one element cannot be changed into
the atom of a different element.
– Atoms cannot be created nor destroyed in any
chemical reaction, only rearranged.
– Every compound is composed of atoms of
different elements, combined in a specific ratio.
J.J. Thomson
• In 1897, J.J. Thomson (another
English scientist) found that
atoms contain negatively
charged particles (electrons).
• Thomson also proposed, based
on other’s experiments, that
atoms must also contain some
sort of a positive charge.
– Thomson describes an atom that
consists primarily of negative
charges scattered throughout a ball
of positive charge (like raisins in a
muffin, or plums in pudding).
Ernest Rutherford
• Ernest Rutherford was a student of
J.J. Thomson.
• In 1911, Rutherford, with the help of
his research team aimed a beam of
positively charged particles at a thin
sheet of gold foil.
– He predicted that the charged particles
would pass through the gold foil in a
straight line, however he noticed that
some of the particles were deflected
strongly!
– Rutherford inferred from this that an
atom’s positive charge (protons) must
be clustered in a tiny region in its
center, called the NUCLEUS!
Rutherford’s Gold Foil
Experiment
•
Rutherford was surprised that a few
particles were deflected strongly.
This led him to propose an atomic
model with a positively charged
nucleus.
Niels Bohr
• In 1913, Niels Bohr, a
Danish scientist, showed
that electrons could have
only specific amounts of
energy causing them to
move in certain orbits
(similar to how the planets
orbit the sun).
The Bohr Model
The Cloud Model
• In the 1920’s, scientists determined that electrons do
not orbit the nucleus like planets, instead electrons
can be anywhere in a cloudlike region around the
nucleus.
– This was known as the “cloud” model and explains that an
electron’s movement is related to its energy level.
– Electrons of different levels are likely to be found in different
places within the atom.
The Modern Atomic Model
• In 1932, English scientist James Chadwick discovered
another particle; the neutron.
• This new particle was hard to discover because it had
no charge, thus was named the neutron!
• The new atomic model explains that at the center of
the atom is a tiny, massive nucleus containing protons
and neutrons. Surrounding the nucleus is a cloudlike
region of moving electrons.
All About the Atom…
• An atom is composed of 3 charged particles:
– The proton (+ positively charged)
– The electron (- negatively charged)
– The neutron (0 no charge)
• Every atom contains a nucleus made up of both
protons (+) and neutrons (0).
• Around the nucleus are electrons (-) at different levels
depending on their specific energy.
Particle Charges
• The charges in an atom balance,
making the atom neutral.
– The number of protons and electrons
must be equal so that the charges
balance.
– Neutrons do not have to equal the
number of protons because they have no
charge.
Particle Masses
• Even though electrons balance protons charge-forcharge, they are not the same size.
• Electrons are so small that it takes almost 2,000
electrons to equal the mass of just one proton.
• Protons and neutrons are about equal in mass.
Size of Atoms
• Atoms are incredibly small, you can’t
see them with the naked eye or even a
microscope!
• Even our most advanced microscopes
can’t show the structure of atoms, they
can only give of glimpse of what they
might look like!
– If the nucleus was the size of your pencil
eraser and you placed it on the pitcher’s
mound of a baseball stadium, the electrons
could be as far away as the top row of
seats!
Atomic Number (page 134)
• Every atom of a given element has
the same number of protons.
– Example: every oxygen atom has 8
protons and every iron atom has 26
protons.
• The number of protons in the
nucleus of an atom is the atomic
number of that atom’s element.
• The definition of an element is
based on its atomic number.
Chemical Symbol
• Every atom of a given element
has a specific chemical
symbol
• The chemical symbol is an
abbreviation of the element’s
name either in Latin or English
– Cu = Copper or cupric
– K = Potassium or kelium
– C = Carbon
– Li = Lithium
Isotopes and Mass Number
• Even though the number of
protons is fixed for a
particular element, the
number of neutrons are not.
• Atoms of the same element
can have different numbers
of neutrons in the nucleus.
– These atoms are called
isotopes.
• Some isotopes are very
unstable and are classified as
radioactive elements.
Isotopes and Mass Number
– Some isotopes are more
common than other isotopes.
• Example: Carbon-12 is more
common than Carbon-13, Carbon14
• Despite the differences in mass, all
carbon isotopes react the same way
chemically!
• Mass Number is the sum of
the protons and neutrons in
the nucleus of an atom.
Atomic Mass
The atomic mass is the
average mass of all the
isotopes of an element
(It is approximately the same as
the number of protons and
neutrons in the nucleus of an
atom).
The Hydrogen Atom
• One electron orbiting a
nucleus
• 1 proton = atomic number
p
• 0 neutrons = 0
e
1H
• Total mass = protons +
neutrons =1
The Helium Atom
• Two electrons orbiting a
nucleus
e
p
n
• 2 protons = 2 = atomic number
n
• 2 neutrons = 2
p
• Total mass = 4 = Protons +
Neutrons = atomic mass
e
4He
Isotopes and Elements
e

p
n
n
If Helium loses one of its
protons (and one of its
electrons), it becomes a
different element
3H (Tritium)
• If Helium loses one of its
neutrons, it becomes an
3He
isotope
e
p
n p
e
How new elements.atoms are
made