Isotopes & Atomic Mass

Atomic Number

Mass Number

Atomic Mass

​Isotopes

Carbon 12

Consider the Atom Carbon, the atomic number tells us the number of protons.

How many protons in Carbon 12?

​Mass No.

​Nuclide Notation

Atomic No - Bottom Left

Mass No - Top Left

Charge if any is at top Right

​How about a carbon atom that has 6 protons and 7 neutrons?

​Mass No.

​Atomic No.

Isotopes

• atoms with the SAME number of PROTONS but DIFFERENT number of NEUTRONS

Multiple Choice

• The atomic number indicates the number of neutrons

• The atomic number indicates the isotope number

• The atomic number indicates the number of protons

• The atomic number indicates the number of protons and neutrons

Multiple Choice

What is the correct definition for isotopes?

• atoms with the same number of protons and neutrons

• Atoms with the same number of protons but different number of neutrons

• Atoms with the same number of neutrons but different number of protons

• Atoms with no mass

Multiple Choice

If you want to determine the total number of protons and neutrons in an atom, you can refer to the

• Mass Number

• atomic number

• symbol

• charge

Lithium isotopes

What do you notice with these 3 isotopes of Lithium?

​Let's look at PHET - Build an Atom

Multiple Choice

What is the difference between these 3 Lithium isotopes?

• no difference

• they have the same atomic number

• they have the same mass number and atomic number

• they have different mass numbers

​So what is the number on the periodic table with decimal places??

​Atomic Mass

​So, what is Atomic Mass

And why is it so important?

​Atomic mass is the "weighted avergage" of all the isotopes of an element.

That way, we don't have to worry which carbon we are dealing with. We just take the AVG carbon.

Multiple Choice

Nitrogen has three occurring isotopes: Nitrogen-13, Nitrogen-14, Nitrogen-15. Nitrogen has an Atomic Mass of 14.007 amu. Which isotope is the most abundant?

• Nitrogen-13

• Nitrogen-14

• Nitrogen-15

• Based on the information given, it cannot be determined

Multiple Choice

Calcium (Atomic Mass = 40.078) has three different isotopes. One has a mass of 35.00 amu; another has a mass of 41.00 amu; and another has a mass of 40.00 amu. Which isotope is the most abundant of the three?

• 40.00 amu

• 41.00 amu

• 35.00 amu

• impossible to tell

Multiple Choice

Chlorine has two naturally occurring isotopes, Cl-35 and Cl-37, The atomic mass of chlorine is 35.45. Which of these two isotopes of chlorine is more abundant?

• Cl-35

• Cl-37

• Cannot be determined from the information provided.

Multiple Choice

Four isotopes of lead include lead-204, lead-206, lead-207, and lead-208.  The average atomic mass of lead is 207.2.  Which isotope of lead is likely to be the most abundant.

• 204

• 206

• 207

• 208