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Isotopes

They are atoms of the same element that have different numbers of neutrons.

0

What Are Isotopes?It’s just a change in the neutrizzle fo shizzle!!!

Hydrogen has 3 numbers of isotopes

There are 3 different “versions” of a hydrogen atom

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An ExampleNote how the number of

protons never change!!!

Hydrogen has 3 numbers of isotopes

There are 3 different “versions” of a hydrogen atom

0

An ExampleHaving more neutrons

increases the mass

Hydrogen has 3 numbers of isotopes

There are 3 different “versions” of a hydrogen atom

0

An ExampleMass number = 1

Mass number = 3

Mass number = 2

0 numbers of

Why does The atomic mass on the periodic table have so many decimal Places?6

C

12.01115

13

Al

26.982

10

Ne

20.180

0 numbers of

Atomic mass1

H

1.00797

This atomic mass is the one number that best represents the mass of all three versions of hydrogen.

0 numbers of

Atomic mass1

H

1.00797

No atom of hydrogen anywhere in the universe actually has this mass.

0 numbers of

Atomic mass1

H

1.00797

This number is a “weighted” average of the masses of every isotope of hydrogen

1. First, you have to know the numbers of mass of each isotope

2. Second, you have to know the percent abundance*of each isotope

*see next slide

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Calculating a “weighted” averagePercent abundance numbers of is how often that particular isotope occurs in a sample of the element

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Percent abundance?A sample of magnesium collected anywhere in the universe will contain three isotopes of magnesium.

Sample of Magnesium

These are the percent abundances of each isotope of magnesium

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Percent abundance?78.90% of this magnesium will be the isotope named “magnesium 24”

10.00% of this magnesium will be the isotope named “magnesium 25”

Sample of Magnesium

11.10% of this magnesium will be the isotope named “magnesium 26”

This data will be provided to you in problems or you will be given a table where you can look it up.

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Percent abundance?78.90% of this magnesium will be the isotope named “magnesium 24”

10.00% of this magnesium will be the isotope named “magnesium 25”

Sample of Magnesium

11.10% of this magnesium will be the isotope named “magnesium 26”

The formula given a table where you can look it up.

(Mass of isotope #1)(percent abundance)

100

(Mass of isotope #2)(percent abundance)

100

(Mass of isotope #3)(percent abundance)

100

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Calculating a “weighted” average0 given a table where you can look it up.

Calculate the atomic mass of magnesium From the given dataUsing the formula for calculating a weighted average given a table where you can look it up.

23.985045(.7890)

+24.985839(.1000)

+25.982595(.1110)

24.306852 amu’s

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Calculating the Atomic mass of magnesiumSince its a “weighted”

average this number

has more influence since

this mass occurs 79% of

the time

It’s NOT just a straight

average where you add

the masses and divide

by 3

Note how the %

abundances were

converted to decimals

(just divide each by 100)

Try another example… given a table where you can look it up.

0 given a table where you can look it up.

Calculate the Atomic Mass of Chromium49.946046( given a table where you can look it up.0.0435)

51.940510(0.8379)

+ 52.940651(0.0950)

53.938882(0.0236)

51.995926 amu’s

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Calculate the atomic mass of chromiumAtomic number given a table where you can look it up. = the number of protons

- It’s the same as the element’s position on the periodic table
- For example, carbon is the 6th element on the table, so its atomic number is 6 which means it has 6 protons (and 6 electrons if it’s a neutral atom)

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Vocabulary reviewAtomic mass given a table where you can look it up. = the “weighted” average mass of all the different isotopes of an atom

- This is the “weird” number on the periodic table that usually has a bunch of places past the decimal point

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Vocabulary reviewMass number given a table where you can look it up. = the sum of protons + neutrons

- This one kind of makes sense because the electrons essentially don’t have any mass
- This HAS to be a whole number because you can’t have part of a proton or neutron
- Mass number is NOT given on the periodic table

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Vocabulary review- What is the mass number of a carbon atom that has 6 neutrons? 7 neutrons?
- How many neutrons does a nitrogen atom have if its mass number is 14?
- How many neutrons does a chlorine atom have if its mass number is 36?
- What is the atomic number of neon?
- What is the atomic mass of neon?

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Let’s Practice Those Terms…A neutrons? 7 neutrons?XZ

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A Short Way to Write Isotopes“A” is the symbol

for Mass Number

(#protons + #neutrons)

“Z” is the

symbol for

Atomic Number

(# of protons)

“X” will be the

symbol of the element

Jay - Z neutrons? 7 neutrons?

Yo! If you’re doin’ chem problems I feel bad for you son….

I got 99 problems, and here’s the first one….HIT ME!!!!

Write neutrons? 7 neutrons?aXz notation for an isotope that has 17 protons and 18 neutrons.

Problem #1Write neutrons? 7 neutrons?aXz notation for an isotope that has 17 protons and 18 neutrons.

35Cl17

Problem #1Write neutrons? 7 neutrons?aXz notation for an isotope that has 19 protons and 21 neutrons.

Problem #2Write neutrons? 7 neutrons?aXz notation for an isotope that has 19 protons and 21 neutrons.

40K19

Problem #2Write neutrons? 7 neutrons?aXz notation for an isotope that has 15 protons, 18 electrons, and 16 neutrons.

Problem #3Write neutrons? 7 neutrons?aXz notation for an isotope that has 15 protons, 18 electrons, and 16 neutrons.

31P3-15

Problem #3This isotope is

also an ion!!!

How many protons, electrons, and neutrons are in this isotope?

41Ca2+ 20

20 protons, 18 electrons, 21 neutrons

Problem #4How many protons, electrons, and neutrons? isotope?

- 56Fe2+26 26, 24, 30
- 27Al3+13 13, 10, 14
- 79Se2-34 34, 36, 45

Write aXz notation for: isotope?

- Isotope with 21 protons, 18 electrons, and 24 neutrons
- Isotope with 53 protons, 74 neutrons, and 54 electrons

Write aXz notation for: isotope?

- Isotope with 21 protons, 18 electrons, and 24 neutrons
45Sc3+21

- Isotope with 53 protons, 74 neutrons, and 54 electrons
127I-53

35 isotope?Cl17 is the same as 3517Cl

Might also see “Cl-35” or “chlorine-35”

Different Forms of AXZ
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