Isotopes and Abundance

Isotopes and Abundance

Mr.Mendoza

Isotopes

an atom of an element with the same number of protons but a different number of neutrons.

Isotopes

Changing neutrons also changes the isotope’s mass number. 

Most elements have many isotopes, so each element is given an average atomic mass.

Lets Analyze,

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Isotope Notation

Look at the picture to the right!

Hydrogen

There are three isotopes of the element hydrogen: protium, deuterium, and tritium.

https://youtu.be/EboWeWmh5Pg

Multiple Choice

Two isotopes of carbon are carbon-12 and carbon-14.  These isotopes differ from one another by two protons.

• true
• false

Multiple Choice

If X is the symbol for an element, which of the following two symbols represent    isotopes of the same element?     I. ⁷⁷₃₅X  II. ⁷⁷₃₃X  III. ⁸¹₃₇X  IV. ⁸¹₃₅ X

• I and II
• III and IV
• I and IV
• I and III

Multiple Choice

Isotopes are atoms of the same element with different #’s of __________ & therefore different __________.

• n⁰ ;  atomic #’s
• p⁺ ; atomic #’s
• e^- ; atomic masses
• n⁰ ; atomic masses

Average Atomic Mass

a weighted average of the masses of an element's isotopes.

Considers the masses of the isotopes AND their percent abundance. 

% Abundance

describes the percent amount (how much) this isotope exists in nature.

Calculating Avg Atomic Mass

Remember:

Every isotope is an atom of the same element

The Overall Abundance must equal 100% in order to represent all isotopes found in nature

Calculating AAM

1. Convert abundance into decimal form

2. Multiply/Combine the average atomic mass with the decimal or...

3.Average Atomic Mass =

(mass of isotope 1 X decimal abundance) + (mass of isotope 2 X decimal abundance)

DONT FORGET THE UNITS!

Multiple Choice

4.35% of all X atoms have a mass of 39.946 amu. 83.79% have a mass of 41.941 amu, 9.50% have a mass of 42.941 amu, and 2.36% have a mass of 43.939 amu. What is the average atomic mass of atom X?

• 41.97 amu
• 42.19 amu
• 10.43 amu
• 40.04 amu

Multiple Choice

24.1% of all the isotopes of a an element have a mass of 75.23 amu, 48.7% have a mass of 74.61 amu, and 27.2% have a mass of 75.20 amu.
What is the average mass of this element?

• 74.92 amu
• 24.97 amu
• 75.01 amu
• 74.51 amu