Transcript Isotopes

1.
I have 22 neutrons and a mass of 40.
2.
I have 37 protons and 39 electrons.
3.
I have 22 neutrons and 19 protons.
At your atom letter, you will finish
your Bohr model of an atom. You
will move around the room
clockwise once finished to look at
everyone else’s atoms. Record p+,
no, e- for each.
Hyphen notation
Element – mass #
Uranium - 238
Nuclear Notation
238
92
U
Topic: Isotopes
p. 35
Obj: understand the conclusions of Bohr’s
nuclear atom. Use isotopic composition to
calculate average atomic mass.
ESQ: How are isotopes similar? Different?
How do you calculate the average atomic
mass of an isotope?
All LIES!
Dalton’s Atomic Theory – the part
that states that atoms of the
same element are identical –
is NOT always true
Isotopes are atoms of the SAME
element that have DIFFERENT
numbers of NEUTRONS and
therefore different masses.
Example:
There are 3 types of Hydrogen
#p:
#p:
#p:
#e:
#e:
#e:
#n:
#n:
#n:
Isotope Notation
#1
-
Hyphen notation
Element name – mass number
Ex 1:
Nitrogen-15
7
How many electrons? ______
7
How many protons? ______
How many neutrons?
8
______
Isotope Notation
2.) Nuclear Symbol
Example 2:
238
92
U
How many protons?
How many electrons?
How many neutrons?
92
92
______
146
______
______
Name
Symbol
Chlorine-37
37Cl
Chlorine-35
Carbon-14
Carbon-12
35 Cl
17
14C
6
12C
Mass
Number
#p
#n
#e
37
17
20
17
35
17
18
17
14
12
6
8
6
6
6
6
Get out page 34 homework por favor…
Put page 36 on the average atomic mass
calculations.
On page 35 (notes), skip a line and put a
subtitle: AVERAGE ATOMIC MASS
◦ An oxygen atom weighs 2.657 x 10-22 g. This
is difficult to use. Way too little!!!
◦ The atomic mass unit (amu) was
developed for the purpose of making
calculations easier. It’s kind of like
“mole.” We made up these units to make
the numbers make more sense.
◦ 1 amu = 1/12th the mass of a Carbon-12 atom

The average atomic mass is a WEIGHTED average
of ALL of the isotopes for an element.

The average atomic mass of a sample of an
element can be found on the periodic table
◦ Ex)
Zinc = 65.39 amu
 The mass of one atom is not exactly the
same as the average mass of many.
◦Ex) 1 atom of Zinc
 65.39
amu
for mass #  p+ + no always equals a whole #
At Haltom, we average grades just like in math. Add up your
grades and divide by the number of grades. This is a typical
average.
Daily – 50%
Major – 50%
63
+74
/
137 2 = 68.5
In another school district, they calculate grades like this:
Daily grades – 40%
Major grades – 60%
63
74
Here since they aren’t equal weights, the average is more
influenced by the major grades since they count as a higher %.
This kid actually gets a 69.6  70 for the six weeks!
means how often it is found





+
+
+
=
(% abundance x mass number isotope 1)
(% abundance x mass number isotope 2)
(% abundance x mass number isotope 3)
etc.
average atomic mass for the element
DO NOT DIVIDE BY ANYTHING!
This is not a regular average.
Don’t forget to change the
percentage to a decimal first!!!
Copper has two naturally occurring
isotopes: copper-63 (69.17%) and
copper-65 (30.83%).
Calculate the average atomic mass of
copper if the relative masses of the isotope
are copper 63 (62.93 amu) and
copper-65 (64.93 amu).
Cu-63 (0.6917 x 62.93 amu)
Cu-65 + (0.3083 x 64.93 amu)
1)
2)
3)
Change % to a decimal
Line up your info.
Use parentheses on calculator if you want to
do it all at once without having to write it
down for each isotope! May try to do it
without them and check the order of
operations. Some calculators know how to
make this work even without the parentheses.
Cu-63 (0.6917 x 62.93 amu)
Cu-65 + (0.3083 x 64.93 amu)
Avg. mass = 63.55 amu
*Notice average is always between
the low & high amu but not
necessarily in the middle.

Naturally occurring boron is 80.20%
boron-11 (atomic mass = 11.01 amu)
and 19.80% of some other isotopic
form of boron. What must the atomic
mass of this second isotope be in
order to account for the 10.81amu
average atomic mass of boron? Round
to the nearest hundredth.

Naturally occurring boron is 80.20% boron-11 (atomic
mass = 11.01 amu) and 19.80% of some other isotopic
form of boron. What must the atomic mass of this
second isotope be in order to account for the 10.81amu
average atomic mass of boron? Round to the nearest
hundredth.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Gold
Tin
Arsenic
Lead
Beryllium
Bromine
Potassium
Chlorine
Sodium
Manganese
11. Ag
12. Hg
13. U
14. Fe
15. Cr
16. I
17. Pt
18. Cu
19. P
20. He

An unknown element, Q, has an average atomic mass of
73.75 amu. The first isotope of Q has a mass of 72.99
amu and the second isotope has a mass of 74.99 amu.
What are the percentages of each isotope?

Remember…
 X
 1-x
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Watch Sig Figs!!!
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Open the container and I will hurt you… F!!!!