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# Isotopes and Mass Number PowerPoint PPT Presentation

Isotopes and Mass Number. Isotope. Atoms of the same element with: Same number of protons BUT Different number of neutrons. ELEMENT IS TO ISOTOPE AS DOG IS TO DOG BREED. Mass Number: Mass of an atom. FLASHBACK: Protons are what animal? Neutrons are what animal?

Isotopes and Mass Number

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## Isotopes and Mass Number

### Isotope

Atoms of the same element with:

Same number of protons

BUT

Different number of neutrons

ELEMENT IS TO ISOTOPE AS DOG IS TO DOG BREED

### Mass Number: Mass of an atom

• FLASHBACK:

• Protons are what animal?

• Neutrons are what animal?

• Electrons are what animal?

• Mass # = mass of the nucleus

• Nucleus = protons + neutrons

• Therefore:

mass# = protons + neutrons

Carbon - 14

Mass Number

C

14

6

Atomic Number

Draw Diagram

• Carbon – 12

C

12

6

6

6

6

6

12

Oxygen - 17

8

O

17

8

8

9

17

9

### Calculating Atomic Mass

• Atomic Mass is the average of all an element’s masses

• You need two values

• Mass of each isotope

• % abundance of each isotope

• Percent abundance is how much of the isotope is represented in the world

### Example: The following is data for the unknown element X. For element Xmass = 6.015abundance = 7.50%

6

7

For element Xmass = 7.016abundance = 92.5%

### Atomic Mass Chart

X - 6

6.015

7.50

45.1

x

X - 7

7.016

x

92.5

649

+

694

6.94 amu

=

100

Find the atomic mass on the periodic table

What is element X?

6.94 amu

The element is Lithium!