Nature of Science
 Bell Ringer: How do you know something
exists if you have never seen it before?
Important Vocabulary
 Inference
 Indirect evidence
The Black Box Lab
Purpose
Materials
Procedure
Results Table (20 pts)
Post Lab Questions (30 pts)
Results (20 pts)
Box #
Inferences
a)
Example
b)
c)
a)
1
b)
c)
Model
Post Lab Questions (30pts)
1.
How did you construct your model of what was in the
boxes?
2.
How do you know if something exists if you have never
seen it before?
3.
How does this lab relate to the scientific method?
4.
To create a more accurate model, what would you
want to do next without looking inside the boxes?
5.
How do you think scientists use or have used empirical
evidence to create models? (hint: think about topics in
this class)
Contents of Each Box
• Box 1- Wooden
block
• Box 2 - 3 Pennies
• Box 3 - 2 Straws
• Box 4 - 10 Stickers
• Box 5 - Pill
Canister
• Box 6 – 2 Rubber
bands
• Box 7 - 1 Dice
• Box 8- 10 Beads
• Box 9 - 10 Lima
Beans
• Box 10 - 2 Cotton
Balls
What does an atom actually
look like?
Closure: watch video “have you
ever seen an atom?”
Exit Pass – how does today’s lab
relate to the discovery of the atom?
Historical Scientists Jigsaw Activity
 It is now your turn to do some research…
 You will be assigned a scientist to become an
expert on
 This scientist had an impact on the historical
development of the atom
 YOUR JOB: give a creative, informative poster on
your scientist and how they influenced the historical
development of the atom
 You are then going to share your poster with others
to inform them about your scientist.
Textbook Info
 Dalton – pg 77-78
 Thomson – pg 79
 Rutherford – pg 81
 Bohr – pg 91
 DeBroglie – pg 91
Atoms
New section in table of contents
Aristotle & Democritus
 First philosophers to start thinking about the
atom and its component
 Smallest divisible component vs. indivisible
particle
Dalton
 Billiard Ball Model
 Provided evidence for how we know atoms
exist
EQ 1: How do we know
atoms exist?
 KC 1: Law of definite proportions – a chemical
compound always contains the same
elements in exactly the same proportions by
weight or mass
 KC 2: Law of conservation of mass
 KC 3: Law of multiple proportions – when 2
elements combine to form 2 or more
compounds, the mass of one element that
combines with a given mass of the other is in
the ratio of small whole numbers
EQ 2: What are the five postulates
of Dalton’s atomic theory
 The ancient Greeks tried to explain matter, but
the scientific study of the atom began with
John Dalton in the early 1800's.
EQ 2: What are the five postulates
of Dalton’s atomic theory
 KC 1: All matter is composed of
extremely small particles called
atoms, which cannot be
subdivided, created, or destroyed
 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
EQ 2: What are the five postulates
of Dalton’s atomic theory
 KC 2: Atoms of a given element are identical
in their physical and chemical properties
 KC 3: Atoms of different elements differ in their
physical and chemical properties
EQ 2: What are the five postulates
of Dalton’s atomic theory
 KC 4: Atoms of different elements combine in
simple, whole-number ratios to form compounds
 KC 5: In chemical reactions,
atoms are combined,
separated, or rearranged
but never created,
destroyed, or changed
Thomson
 Plum pudding model
 Introduced the idea that electrons are located
outside the nucleus
Rutherford
 Discovered the
nucleus
 Used the gold foil
experiment
EQ 3: What model of the atom
will we use?
 KC 1: Bohr suggested that electrons move in
circular orbitals around the nucleus
 Bohr’s model of the atom gives us a good
starting point for understanding more about
the atom
EQ 3: What model of the
atom will we use?
KC 2: How 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 circular orbits the atom
has.
4) Add electrons = atomic number
- 1st shell can hold two
- 2nd and 3rd can hold eight
Bohr model of the atom
 Elements in the 1st period
have one energy level.
 Elements in the 2nd period
have two energy levels,
and so on.
Bohr model of the atom
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 model of the atom
Element name
Atomic number =
number of protons =
number of electrons
(for now…)
Element symbol
Average atomic mass
Bohr model of the atom
C
 Add the electrons.
 Carbon has 6
electrons.
 The first shell can only
hold 2 electrons.
Bohr model of the atom
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 model of the atom
C
 Check your work.
 You should have 6 total
electrons for Carbon.
 Only two electrons can fit
in the 1st shell.
 The 2nd shell can hold up
to 8 electrons.
 The 3rd shell can hold 18,
but the elements in the
first few periods only use 8
electrons.
Bohr model of the atom
 KC 3: The lowest allowable energy state of an
atom is called its ground state.
 KC 4: When an atom gains energy, it is in an
excited state.
 Wavelike properties of electron help relate
atomic emission spectra, energy states of
atoms, and atomic orbitals
Bohr model of the atom
 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 model of the atom
 KC 5: 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.
Bohr model of the atom
 KC 6: The behavior of electrons is still not fully
understood, but it is known that they do not
move around the nucleus in circular orbits
 We use Bohr’s model because it is easy to
picture and gives us a basic understanding of
the atom
Whiteboard Practice
Draw the Bohr model for the following
elements:
Boron
Calcium
Chlorine
Nitrogen
EQ 4: What is an atom made of?
Know
Want to know
Learned
EQ 4: What is an atom made of?
 KC 1: An atom is made of a nucleus
containing protons and neutrons. Electrons
move around the nucleus.
EQ 4: What is an atom made of?
 KC 2: The number of protons and the mass
number define the identity of the atom
 Each element contains a unique positive
charge in their nucleus
What is an atom made of?
 KC 3: The number of protons in the nucleus of
an atom identifies the element and is known as
the element’s atomic number
Atoms and Isotopes
 All atoms of a particular element have the
same number of protons and electrons but the
number of neutrons in the nucleus can differ
 KC 4: Atoms with the same number of protons
but different numbers of neutrons are called
isotopes
Atomic Mass and Isotopes
 The relative abundance of each isotopes is
usually constant
 Isotopes containing more neutrons have a
greater mass
 Isotopes have the same chemical behavior
 KC 5: The atomic mass is the sum of the
protons and neutrons in the nucleus
Atomic Mass and Isotopes
Isotopes
 There are 2 ways you will see isotopes written:
Aluminum-27
27
13
Al
Atomic Mass
 One atomic mass unit (amu) is defined as
1/12th the mass of a carbon-12 atom
 One amu is nearly, but not exactly, equal to
one proton and one neutron.
Calculating Averages
 If you are shopping, and something is $24.99
and 15% off, how much would you pay?
Average Atomic Mass
 KC 6: The average atomic mass of an element
is the weighted average mass of the isotopes
of that element
Average Atomic Mass
 Average atomic mass = (mass1 x abundance1) +
(mass2 x abundance2) + …
Istotope
Mass
Abundance
Total
Mg - 24
23.985
0.7870
18.876
Mg - 25
24.986
0.1013
2.531
Mg - 26
25.983
0.1117
2.902
Average atomic mass =
24.309 amu
Practice Problems
1. The four isotopes of lead and its abundances are:
Pb-204, 1.37%; Pb-206, 26.26%; Pb-207, 20.82%; and
Pb-208, 51.55%. Calculate lead’s approximate
atomic mass.
Istotope
Mass
Abundance
Pb-204
Pb-206
Pb-207
Pb-208
Average atomic mass =
Total
Practice Problems
2. Calculate the average atomic mass of neon if
neon exists naturally as 90.92% neon-20,
0.257% neon-21, and 8.82% neon-22.
Istotope
Mass
Abundance
Average atomic mass =
Total
Practice Problems
3. Titanium has 5 common isotopes: 46Ti (8.0%),
47Ti (7.8%), 48Ti (73.4%), 49Ti (5.5%), 50Ti (5.3%).
What is the average atomic mass of titanium?
EQ 5: How do you determine the
number of protons, neutrons, and
electrons in an atom?
 Atom Basics – building blocks of chemistry
 These are must knows!!
You must be able to answer
the following questions…
1.
What is my name?
2.
What is my atomic number?
3.
What is my average atomic mass?
4.
(Pick one of my isotopes on the left side of the card). What would the atomic mass of that
particular atom?
5.
How many protons do I have?
6.
How many neutrons do I have?
7.
How many electrons do I have if I am neutral?
8.
(Pick an ion of the right side of the card). How many protons and electrons do I have?
9.
(Consider that I am the previous chosen isotope above and a neutral atom) What
happens to me if I gain a
p+_________ no_________ e- ________
10.
What happens to me if I lose a
p+_________ no_________ e- _________
1. What is my name?
2. What is my atomic number?
 KC 1: An atom’s atomic number is equal to the
number of protons, which is found on the
periodic table
3. What is my average atomic
mass?
 KC 2: Average atomic mass is the averages of
all of the isotopes of an element. This number is
calculated and based on abundance, but
also found on the periodic table.
4. What is the atomic mass of
a particular isotope?
5. How many protons do I have?
 KC 3: The number of protons is equal to the
atomic number, which is found on the periodic
table
6. How many neutrons do I have?
 KC 4: The atomic mass = protons + neutrons
 Atomic number = number of protons
 KC 5: neutrons = atomic mass – atomic
number
7. How many electrons do I
have if I am neutral?
 KC 6: The number of electrons is equal to the
number of protons in a neutral atom
8. How many protons and neutrons
do I have if I am neutral?
 If the atom is neutral, the protons and neutrons
are found from the atomic mass and atomic
number of that particular isotope
 Protons = atomic number
 Neutrons = atomic mass – atomic number
9. & 10. What happens if I
gain/lose a p+, n0, and e-?
 KC 7: When the number of protons changes,
the identity of the element changes
 KC 8: When the number of neutrons changes,
the atomic mass changes
 KC 9: When the number of electrons changes,
the atom is no longer neutral and has a charge
What happens if I gain/lose a
p+, n0, and e-?
 Example: Calcium – 40
p+________________ no________________ e- _________________
1.
What is my name?
2.
What is my atomic number?
3.
What is my average atomic mass?
4.
(Pick one of my isotopes on the left side of the card). What
would the atomic mass of that particular atom?
5.
How many protons do I have?
6.
How many neutrons do I have?
7.
How many electrons do I have if I am neutral?
8.
(Pick an ion of the right side of the card). How many protons
and electrons do I have?
9.
(Consider that I am the previous chosen isotope above and a
neutral atom) What happens to me if I gain a
p+_________ no_________ e- ________
10. What happens to me if I lose a
p+_________ no_________ e- _________