Transcript The Atom

Unit 6- The Atom
Key Concept 1: The ancient
Greeks tried to explain
matter, but the scientific
study of the atom began
with John Dalton in the early
1800's.
MOST IMPORTANT
CONCEPT IN SCIENCE
Greek Philosophers
• Many ancient scholars believed matter was
composed of such things as earth, water,
air, and fire.
• Many believed
matter could be
endlessly divided
into smaller and
smaller pieces.
Greek Philosophers (cont.)
• Democritus (460–370 B.C.) was the first
person to propose the idea that matter was
not infinitely divisible, but made up of
individual particles called atomos.
• Aristotle (484–322 B.C.) disagreed with
Democritus because he did not believe empty
space could exist.
• Aristotle’s views went unchallenged for 2,000
years until science developed methods to test
the validity of his ideas.
Greek Philosophers (cont.)
Greek Philosophers (cont.)
• John Dalton revived the idea of the atom in
the early 1800s based on numerous
chemical reactions.
• Dalton’s atomic theory easily explained
conservation of mass in a reaction as the
result of the combination, separation, or
rearrangement of atoms.
Greek Philosophers (cont.)
What were the errors in the Dalton’s Atomic Theory?
Get out your Nature of Science Handout
John Dalton : Atomic Theory 1811 (First on timeline)
Greek Philosophers (cont.)
Key Concept 2: An atom is the
smallest particle of an element
that retains the properties of that
element.
The Atom
• Once scientist were convinced of the
existence of an atom, a new set of question
emerged.
• What is an atom like?
• Although many scientist researched an atom
in the 1800’s, it was not until almost 1900 that
some of these questions were answered.
• Twilight Zone
1897
University of
Cambridge in England
The Atom
• Cathode Ray Tube
Key Concept 3:
J.J. Thomson
(1856-1940)
The Electron (cont.)
• This figure shows a typical cathode ray
tube.
The Electron (cont.)
• J.J. Thomson and his team of scientist measured
the effects of both magnetic and electric fields on
the cathode ray to determine the charge-to-mass
ratio of a charged particle, then compared it to
known values.
• The mass of the charged particle was much less than
a hydrogen atom, then the lightest known atom.
• (KC 3, Cont.) J.J. Thomson had discovered the
electron in 1897, the later received the Nobel Prize in
1906 for identifying the first subatomic particle—the
electron.
The Electron
• When an electric charge is applied, a ray of
radiation travels from the cathode to the
anode, called a cathode ray.
• Cathode rays are a stream of particles
carrying a negative charge (electron).
Board Meeting
Propose an new model of an atom that will
account for the discovery of an the electron.
- 5 minutes
- Draw a picture as a Lab Table
- Present idea to class
- Use different color
- Label if needed
The Electron (cont.)
• Matter is neutral.
• William Thomson in 1902
(later elevated to Lord Kelvin)
proposed that the atom have
the newly discovered
electrons embedded
somehow in a sphere of
uniform positive charge, this
sphere being the full size of
the atom.
The Electron (cont.)
• This picture was taken up by J. J. Thomson too, and was
dubbed the plum pudding model, after traditional English
Christmas fare, a large round pudding with raisins
embedded in it.
• (KC 3, Cont.) J.J. Thomson's plum pudding model of the
atom states that the atom is a uniform, positively charged
sphere containing electrons.
The Atom
• Oil Drop Experiment 1
• Oil Drop Experiment 2 and 3
Key Concept 4:
R. Millikan
(1868-1953)
The Electron (cont.)
• (KC 4, Cont.) In 1909, Robert Millikan used
the oil-drop apparatus shown below to
determine the charge of an electron.
The Electron (cont.)
• Charges change in discrete amounts—
1.602  10–19 coulombs, the charge of one
electron.
• (KC 4, Cont.) Now, chemists choose to use
a relative charge is equated to a single
unit, 1–.
• With the electron’s charge and charge-tomass ratio known, Millikan calculated the
mass of a single electron.
the mass of
a hydrogen
atom
The Electron (cont.)
• J.J. Thomson's plum pudding model of the atom states
that the atom is a uniform, positively charged sphere
containing electrons.
• How could you
test this model?
END DAY
Important Vocabulary:
Inference
Empirical (indirect) evidence
The Black Box Lab
•
•
•
•
•
Purpose (5 pts)
Materials
Procedure
Results Table (20 pts)
Post Lab Questions (25 pts)
12
12
Results (20 pts)
Lab
Station #
Inferences
a)
b)
c)
Note: You will not rotate to every
station, time will tell how far we get
Model
7 min- Post Lab Questions (25pts)
1. (5 pts) How did you construct/know what to
draw for your model of what was in the boxes?
2. (5 pts) How do you know if something exists if
you have never seen it before?
3. (5 pts) To create a more accurate model, what
would you want to do next without looking
inside the boxes?
4. (5 pts) How do you think scientists use or have
used indirect evidence to create models?
5. (5pts) After watching the cube example, is
anything for sure in science? How does this
relate to the nature of science?
Get Out Your Nature of
Science Handout
• Science never stops, discoveries lead to
questions which lead to discoveries which
lead…
• Scientific ideas are always based on evidence
(in chemistry indirect evidence is important)
What is in the atom?
It is like a very, very small black box.
The Atom
• Gold Foil Experiment 1
• Gold Foil Experiment 2
Key Concept 5:
Rutherford
(1871-1937)
The Nucleus
• In 1911, Ernest Rutherford studied how
positively charged alpha particles
interacted with solid matter.
• By aiming the particles at
a thin sheet of gold foil,
Rutherford expected the
paths of the alpha
particles to be only
slightly altered by a
collision with an electron.
The Nucleus (cont.)
The Nucleus (cont.)
• Although most of the alpha particles went
through the gold foil, a few of them
bounced back, some at large angles.
The Nucleus (cont.)
• (KC 5, Cont.) Rutherford concluded that
atoms are mostly empty space.
• (KC 5, Cont.) Almost all of the atom's
positive charge and almost all of its mass is
contained in a dense region in the center of
the atom called the nucleus.
• Electrons are held within the atom by their
attraction to the positively charged nucleus.
The Nucleus (cont.)
• The repulsive force between the positively
charged nucleus and positive alpha
particles caused the deflections.
The Nucleus (cont.)
• (KC 5, Cont.) Rutherford refined the model
to include positively charged particles in
the nucleus called protons.
• The term proton itself seems to have been
coined by Rutherford, and first appears in
print in 1920.
Contents of Each Box ?????
• Who knows?
• Will we ever know? Can we ever
say for sure?
What does an Atom Actually look like?
Closure: watch video “Have you ever seen an atom”
End of Day
Close Read Directions
1. ( 10 min) Independently read (slowly) and
annotate – circle important words, underline
important facts, write “?” Next to anything you
don’t understand
2. (10 min) Think about the reading and discuss it
with your shoulder partner (Get a discussion
stamp)
3. Listen to the teacher read…listen for more
4. Answer questions: CITE with EVIDENCE from the
text
•The Atom
Key Concept 6:
Niels Bohr
(1885-1962)
Bohr's Model of the Atom
• (KC 6, Cont.) Bohr was a
student of Rutherford,
and came up with a new
atomic model in 1913.
He proposed that
electrons are arranged
in circular patterns
around the nucleus.
Bohr's Model of the Atom (cont.)
• Bohr suggested that an electron moves
around the nucleus only in certain allowed
circular orbits.
Bohr's Model of the Atom (cont.)
• Key Concept 7: (How fireworks work)
• The lowest allowable energy state of an
atom is called its ground state.
• When an atom gains energy, it is in an
excited state.
• Hydrogen’s single electron is in the n = 1
orbit in the ground state.
• When energy is added, the electron moves to
the n = 2 orbit.
Bohr's Model of the Atom (cont.)
• A photon is a particle of electromagnetic
radiation having zero mass and carrying a
quantum of energy.
• When a photon strikes an atom it gives the
atoms more energy. If enough photons
strike an atom it may cause electrons to
jump levels.
Bohr's Model of the Atom (cont.)
• The excited state occurs when an atom
has a higher potential energy than it has at
its ground state.
• When an excited atom falls back to its
ground state the substance will give off a
unique color of light.
• Demo
Bohr's Model of the Atom (cont.)
Key Concept 8: Steps to draw a Bohr model of an atom
1) Find your element on the periodic table.
2) Determine the number of electrons – it is the same as the
atomic number.
3) Determine the number of energy levels or circular orbits the
atom has– it is the same as the period number.
4) Add electron = atomic number
- 1st shell can hold two
- 2nd and 3rd can hold eight
Bohr's Model of the Atom (cont.)
• Elements in the 1st
period have one
energy level.
• Elements in the 2nd
period have two
energy levels, and so
on.
Bohr's Model of the Atom (cont.)
•
C
•
•
Draw a nucleus with
the element symbol
inside.
Carbon is in the 2nd
period, so it has two
energy levels, or shells.
Draw the shells around
the nucleus.
Bohr's Model of the Atom (cont.)
•
•
C
•
Add the electrons.
Carbon has 6
electrons.
The first shell can only
hold 2 electrons.
Bohr's Model of the Atom (cont.)
•
C
•
•
Since you have 2
electrons already
drawn, you need to
add 4 more.
These go in the 2nd
shell.
Add one at a time starting on the right
side and going counter
clock-wise.
Bohr's Model of the Atom (cont.)
•
•
Check your work.
You should have 6 total
electrons for Carbon.
Only two electrons can
fit in the 1st shell.
The 2nd and 3rd shells
can hold up to 8
electrons.
After the 3rd shell, things
get complicated………..
•
C
•
•
•
•
4th /5th can hold 18 e
6th/7th can hold 32 e
You try it….. Stamping time
• Draw the Bohr Model
for
– Boron
– Sulfur
End of Day
Let’s do a little review
Let’s do a little review
Move into shoulder partners
• Following the steps in Key Concept 8 and draw
the Bohr Model.
–Fluorine
–Sodium
–Argon (don’t erase)
Let’s do a little review
• Bohr’s model of the atom failed to explain
spectral lines outside of hydrogen
Electron location or their configuration: 1s2 2s2 2p6 3s2 3p6
Model of the Atom
• NAU has recruited you to help assign
students to one of the new dorm facilities that
will open for the spring semester.
• There are four types of dorm rooms in the
building
• s-super rooms
• p-pretty good rooms
• d-dumpy rooms
• f-fantastically bad rooms
Rules for assigning students to dorm rooms
1. Maximum of two students in any one room
2. There are no elevators--- students must be as
close to the 1st floor as possible
3. When filling a type of room, all rooms must be
full before going onto a different type of room.
4. When filling a type of room on a floor, you must
place one student in each type of room before
pairing them.
Example: 14 students
Model of the Atom
• NAU now would like us to document the placement of
student in a uniform easy to understand way
Here is an example: 1s2 2s2 2px2y2z2 3s2 2px1
• Big Numbers for floors
• Letters for type of room
• Super script for number of students in the room
• Sub script to distinguish the different rooms of the same
type/same floor
Model of the Atom
1. Semester 1: 9 students
Please complete number 1 on your boards first and
then your worksheet.
Model of the Atom
1. 9 students
Answer: 1s2 2s2 2px2y2z1
Model of the Atom
2. 15 students
Please complete number 2 on your boards, but
NOT on your worksheet.
Answer: 1s2 2s2 2px2y2z2 3s2 3px1y1z1
Short Hand Example:
Model of the Atom
• The administration of the college has been
approached by students complaining that
they don’t like being put in poor quality rooms
when there are much better rooms on the
next floor or two higher.
• In light of these complaints the school has
instituted a new rule which may be followed
when placing students into dorm rooms.
• “A student will be placed one floor higher if
and only if there is an available room, which
is two grades better.”
Model of the Atom
• Due to the complicatedness of this new rule
NAU has provided you with the following
chart to aid in student placement.
Model of the Atom
3. 50 students
Exit Ticket- Write what each part of the following
electron configuration means: 2p3
End of Day
Model of the Atom
On worksheet complete 1-3 as review
(these are the same question we did
yesterday on white boards) with your
shoulder partners
4. 62 students
Okay Mrs. Askew, this is Chemistry class right.
•Students = electrons
•Floors = energy levels
•Room types = shape of orbitals
•Rules for filling rooms are actually a
hierarchy of energy requirements
1.
Maximum of two students in any one room
•Aufbau Principle
2.
There are no elevators--- students must be
as close to the 1st floor as possible
•Paul’s Exclusion Principle
3.
When filling a type of room, all rooms must
be full before going onto a different type of
room.
When filling a type of room on a floor, you
must place one student in each type of room
before pairing them.
•Hund’s Rule
4.
Let’s do a little review
Show 3D Models
The Quantum Mechanical Model of the Atom
• Key Concept 9: Louis de Broglie (1892–1987)
hypothesized that particles, including electrons,
could also have wavelike behaviors in 1924.
• The de Broglie equation predicts that all moving
particles have wave characteristics.
 represents wavelengths
h is Planck's constant.
m represents mass of the particle.
 represents frequency.
The Quantum Mechanical Model of the Atom (cont.)
• Key Concept 10: Schrödinger
treated electrons as waves in a
model called the quantum
mechanical model of the atom
1925.
• This model was a mathematical
equation describing the location
and energy of electron.
The Quantum Mechanical Model of the Atom (cont.)
• Schrödinger’s equation is to complex to be allowed in
my classroom.
• However, each solution of the equation in known as a
wave function, which is the related to the probability
of finding the electron within a particular volume of
space around the nucleus.
The Quantum Mechanical Model of the Atom (cont.)
• The wave function predicts a threedimensional region around the nucleus
called the atomic orbital ( or electron
cloud).
The Quantum Mechanical Model of the Atom
• Step by step, scientists such as Rutherford,
Bohr, and de Broglie had been unraveling the
mysterious of the atom.
• However, a conclusion reached by a German
theoretical physicists proved to have a profound
implication for the atomic model.
• Key Concept 11: Werner Heisenberg (19011976)
The Quantum Mechanical Model of the Atom (cont.)
• (KC 11, Cont.) Heisenberg showed it is
impossible to take any measurement of an
object without disturbing it.
• The Heisenberg uncertainty principle (1927)
states that it is fundamentally impossible to
know precisely both the velocity and position
of a particle at the same time.
• The only quantity that can be known is the
probability for an electron to occupy a certain
region around the nucleus.
The Quantum Mechanical Model of the Atom (cont.)
Key Concept 12: A set of
three rules determines the
arrangement of electrons in
an atom (Electron
Configuration).
Ground-State Electron Configuration
• The arrangement of electrons in the atom
is called the electron configuration.
• Key Concept 13: The aufbau principle states
that each electron occupies the lowest energy
orbital available.
Ground-State Electron Configuration (cont.)
Ground-State Electron Configuration (cont.)
• Key Concept 14: The Pauli exclusion
principle states that a maximum of two
electrons can occupy a single orbital, but
only if the electrons have opposite spins.
Ground-State Electron Configuration (cont.)
• Key Concept 15: Hund’s rule states that single
electrons with the same spin must occupy each
equal-energy orbital before additional electrons
with opposite spins can occupy the same
energy level orbitals.
Pass Out Periodic Table and Glue
Ground-State Electron Configuration (cont.)
• Key Concept 16: Noble gas notation uses
noble gas symbols in brackets to shorten
inner electron configurations of other
elements.
Electron Configuration Practice
• Homework– (Due on Monday)
Exit Pass
• Remember, that I paired electron
when I drew Bohr models.
• Based on what you have
learned today, why do electrons
have to be “paired”?
• Things to keep in mind
• How many students to a
room?
• How many electron to an
orbital?
End of Day
The Atom
• The neutron
Key Concept 17:
J. Chadwick
(1891-1974)
James Chadwick received the
Nobel Prize in 1935 for
discovering the existence of
neutrons in 1932, neutral
particles in the nucleus which
accounts for the remainder of an
atom’s mass.
The Nucleus (cont.)
• All atoms are made of three
fundamental subatomic
particles: the electron, the
proton, and the neutron.
• Atoms are spherically
shaped.
• Key Concept 18: Atoms are
mostly empty space, and
electrons travel around the
nucleus held by an attraction
to the positively charged
nucleus.
The Nucleus (cont.)
• Key Concept 19:
The Nucleus (cont.)
• Scientists have determined that protons
and neutrons are composed of subatomic
particles called quarks (1968).
Section 5.2 Assessment
Atoms are mostly ____.
A. positive
B. negative
C. solid spheres
D. empty space
A.
B.
C.
D.
A
B
C
D
Section 5.2 Assessment
What are the two fundamental
subatomic particles found in the
nucleus?
A. proton and electron
B. proton and neutron
C. neutron and electron
D. neutron and positron
A.
B.
C.
D.
A
B
C
D