Do Now
 As soon as you enter the room your voice is off
 Pick up a New Do Now Form, a study guide, and the daily
handout
 Find your assigned seat and get started on the following Do
Now in your Do Now form:
Which of the following atoms are isotopes of each other?
1. X: 11 protons, 12 neutrons
2. Y: 11 protons, 11 neutrons
3. V: 12 protons, 11 neutrons
4. W: 11 protons, 13 neutrons
A: 1, 3 B: 1,2,4 C: all of them D: none of them
Review of Procedures
1.
2.
3.
4.
5.
Raise your hand to speak and wait to be recognized
If I don’t answer your question – put it on a sticky
note and put it in the parking lot before you leave.
Do not get up out of your seat without permission.
No heads down.
Enter silently, pick up any handouts, find your
assigned seat, start the Do Now immediately.
All atoms of the same element
have the same number of protons,
but the number of neutrons may
vary.
Isotopes are atoms of the same
element which have different
numbers of neutrons.
Isotope
Oxygen – 16
Oxygen – 17
Oxygen - 18
Nuclear Number
Symbol of Protons
8
8
8
Number
of
Electrons
8
8
8
Number
Mass
of
Number
Neutrons
8
9
10
16
17
18
Mass
(amu)
15.99415
16.999131
17.999160
What structural characteristics do all oxygen atoms have in
common? All oxygen atoms have the same number of protons and electrons.
What differences exist between the isotopes of oxygen?
The mass number, number of neutrons and mass of each isotope are different.
The isotopes of an element do not differ significantly in their
chemical behavior. Why do you think this is so?
The chemical behavior is determined by the number of electrons and they all
contain the same number of electrons.
The average atomic mass for an
element is given on the periodic
table, but how was it determined?
In order to calculate the average
atomic mass for an element, you
must know the percent abundance
and atomic mass for each of the
isotopes of that element.
Isotope
Atomic Mass
Oxygen – 16
Oxygen – 17
Oxygen – 18
15.99415 amu
16.999131 amu
17.999160 amu
Percent
Abundance
99.762%
0.038%
0.200%
The average atomic mass of oxygen is given as 15.999 amu on the
periodic table. Let’s see how that was calculated.
15.99415 amu ×
= 15.95608 amu
16.999131 amu x
= 0.0064597 amu
17.99160 amu ×
= 0.03598 amu
15.95608 amu + 0.0064597 amu + 0.03598 amu = 15.999 amu
A certain element exists as three natural
isotopes as shown in the table below.
Isotope
Mass (amu)
Percent
Abundance
Mass Number
1
19.99244
90.51
20
2
20.99395
0.27
21
3
21.99138
9.22
22
Calculate the average atomic mass of this element to the nearest
thousandth.
19.99244 amu ×
20.99395 amu ×
21.99138 amu ×
= 18.09515744 amu
= 0.056683665 amu
= 2.027605236 amu
18.09515744 amu + 0.056683665 amu + 2.027605236 amu = 20.179 amu
Identify the element. Neon
Carbon has three naturally occurring
isotopes: Carbon-12 (12.000 amu), Carbon13 (13.003 amu), and Carbon-14 (14.003
amu). Based upon the average atomic mass
of carbon (12.011 amu), which isotope of
carbon do you think is the most abundant in
nature? Explain your answer.
Carbon-12 is the most abundant in nature.
This answer is based on the fact that the
average atomic mass of carbon is 12.011
amu which is closest to the mass of carbon12.
An element has two naturally occurring isotopes.
The mass of the first isotope is 64.9278 amu and
the mass of the second isotope is 62.9296 amu.
The average atomic mass of the element is
63.546 amu. Calculate the percent abundance of
each isotope to two decimal places.
Let x = the percent as a decimal of the first isotope.
1-x = the percent as a decimal of the second isotope.
(64.9278)x + (1-x)(62.9296) = 63.546
64.9278x + 62.9296 – 62.9296x = 63.546
1.9982x = 0.6164
x = 0.3085; 1-x = 0.6915
The percent abundances are 30.85% and 69.15%.
Beanium
 Be sure to have all information and calculations
recorded for the Beanium activity from Friday
 Using the Cl-Ev-R model to report on activity
Ions are formed when an atom gains or
loses electrons.
• anion – negatively charged ion formed
when an atom gains electrons
• cation – positively charged ion formed
when an atom loses electrons
We will talk more about ions later this
year.
• determined by the number of
protons in the nucleus
• found on the periodic table
Determine the atomic number for
each of the following elements.
Li
3
N
7
12
Mg
• equal to the sum of the neutrons
and protons in the nucleus of an
atom
• not given on the periodic table
Ways to indicate mass number:
•Hyphen notation
Chlorine-35
•Nuclear Symbol
Beryllium-9
Determine the number of neutrons in
Argon-40.
The atomic number for argon is 18.
40 - 18 = 22.
Element
(hyphen
notation)
Nuclear
Symbol
Atomic
Mass
Number Number
Number Number Number
of
of
of
Protons Neutrons Electrons
Sodium -22
11
22
11
11
11
Fluorine-19
9
19
9
10
9
Bromine-80
35
80
35
45
35
Calcium-40
20
40
20
20
20
Hydrogen-1
1
1
1
0
1