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Physical Science
Atoms—Day 9
Materials Needed:
Writing Utensil
Folder
Notebook
Day 9
• Bell Work: What happens if an atom of Oxygen gains a
electron? What happens if it loses an electron? What
about if it gains a neutron?
• Agenda:
• Notes on Isotopes
• Isotope Demo
• Calculating Average Atomic Mass
• Finish Isotope Lab/Exit Slip
Q1: What is air pressure?
A. It is the measure of the movement of the air
molecules.
B. It is the measure of the air molecules push on a
surface.
C. It is the measure of the amount of oxygen in the
atmosphere.
D. It is the measure of the amount of nitrogen in
the atmosphere.
S.C.8.4.3b DOK1
Q2: How are elements and compounds
related?
A. Elements and compounds are not related.
B. An element can be broken down into compounds.
C. A compound is two or more elements chemically
combined.
D. An element is two or more compounds chemically
combined.
SC8.2.1.a DOK 2
Mathematics Booster
What is the
percent by
mass of each
type of nut in
can A?
We calculated
percentages for
peanuts
Can A = 44.19%
Greek/Latin
Greek/Latin
Meaning
pro
in front of, first
a-
not, without
tom
cut, incision
-ide
a thing connected
with or belong to
iso
same
Picture
Today’s Objectives
• I will know how isotopes form.
• I will be able to calculate the atomic mass of an element
based on percentages of isotopes.
Bell Work Answer
• What happens if an atom of Oxygen gains a electron?
What happens if it loses an electron? What about if it
gains a neutron?
A1: What is air pressure?
A. It is the measure of the movement of the air molecules.
Air molecules do not need to be moving in order to create
pressure just like a stack of books on your head does not need
to be moving in order to create pressure on your head.
B. It is the measure of the air molecules pushing on a surface.
Air is made up of many different components, mostly Nitrogen
and Oxygen, that are pressing down on you like a stack of
books.
C. It is the measure of the amount of oxygen in the atmosphere.
Oxygen is only a part of what makes up all of the air molecules
pushing down on a surface.
D. It is the measure of the amount of nitrogen in the atmosphere.
Nitrogen is only a part of what makes up all of the air
molecules pushing down on a surface.
S.C.8.4.3b DOK1
A2: How are elements and compounds
related?
A. Elements and compounds are not related.
Elements and compounds ARE related. It takes two or
more elements chemically combined to make a
compound.
B. An element can be broken down into compounds.
Elements cannot be broken down into compounds, but
compounds can be broken down into elements through
a chemical reaction.
C. A compound is made out of two or more elements.
Two or more elements chemically combine to make a
compound. For example, CO2 (carbon dioxide).
D. An element is made out of two or more compounds.
Elements are not made out of compounds.
SC8.2.1.a DOK 2
Can A
Almonds 47.02 = 13.64%
344.79
Brazil Nut 57.88 = 16.79%
344.79
Cashew
46.20 = 13.40%
344.79
Hazel Nut 19.90 = 5.77%
344.79
Pecan
21.40
= 6.20%
344.79
• Math Talk: using the mass
of the specific nut is divided
by the total mass of all the
nuts. That product is them
multiplied by 100 to
determine the percentage.
Introduction to Isotopes
• http://education-portal.com/academy/lesson/isotopesand-calculation-of-a-weighted-average.html#lesson
Isotopes
• Isotopes are atoms of the same element type that
have different numbers of neutrons
 Neutrons have NO CHARGE, so they only
change the mass of the atom .
These are all atoms of hydrogen
One way to show Isotopes:
Carbon-12
Atomic Mass
Protons
Electrons
Neutrons
Carbon-14
Let’s Practice
Oxygen has 3 isotopes:
•oxygen-16
•oxygen-17
•oxygen-18
Oxygen-16
Oxygen-17
Oxygen-18
Atomic Mass
Protons
Electrons
Neutrons
• How many of each subatomic particle are in each of
the isotopes of oxygen?
A second way to show Isotopes
12
6
C
14
6
C
Let’s Practice
• Write the symbols for the following
isotopes using isotope notation.
24
A.) Magnesium – 24
12
B.) Carbon – 13
13
C.) Silver – 108
6
Mg
C
108
47
Ag
Let’s Practice
Calculate the number of protons, neutrons, and electrons in
an atom of zirconium-90 that has no overall charge and
an atomic number of 40.
Answer
Number of protons =
atomic number 40
Number of neutrons =
mass number – atomic number = 50
Number of electrons =
number of protons = 40
What do you think?
• Why is the atomic mass on the periodic table not a
whole number?
• http://phet.colorado.edu/en/simulation/isotopes-andatomic-mass
Calculating the Mass of an Element
• The atomic mass of an element is the weighted average
of the masses of all the naturally occurring isotopes of
that element.
Calculating Atomic Mass
Chlorine-35 makes up 76% of all the chlorine in nature, and
chlorine-37 makes up the other 24%. What is the atomic
mass of chlorine?
Step 1: Multiply the mass number of each isotope by its
percentage abundance in decimal form. (35 x 0.76) = 26.60
(37 x 0.24) = 8.88
Step 2: Add these amounts together to find the atomic mass.
26.60 + 8.88 = 35.48 amu
Let’s Practice
The metal thallium occurs naturally as 30% thallium-203
and 70% thallium-205. Calculate the atomic mass of
thallium.
(0.30 x 203 amu) + (0.70 x 205 amu) =
204.4 amu
Let’s Practice
Calculate the atomic mass of gallium, which consists of
60% gallium-69 and 40% gallium-71.
(0.60 x 69 amu) + (0.40 x 71 amu) =
69.8 amu
Solve the Following Problems
1. Calculate the atomic mass of boron, which occurs
naturally as 20% boron-10 and 80% boron-11.
2. Calculate the atomic mass of rubidium, which occurs
naturally as 72% rubidium-85 and 28% rubidium-87.
3. Calculate the atomic mass of silicon, which occurs
naturally as 92% silicon-28, 5% silicon-29, and 3%
silicon-30.
Solutions
1. (0.20 x 10 amu) + (0.80 x 11 amu) = 10.8 amu
2. (0.72 x 85 amu) + (0.28 x 87 amu) = 85.56 amu
1. (0.92 x 28 amu) + (0.05 x 29 amu) + (0.03 x 30
amu) = 28.11 amu
Isotope Activity
• Work with your group to gather your data. Record your
data in the first two columns.
• DO NOT open the bags.
• Complete the vocabulary and questions portion for next
class.
Homework
• Atomic Changes Worksheet (1/2 sheet of paper)
Exit Slip
• Explain an isotope.