Loading in 5 sec....

Calculations in Chemistry:PowerPoint Presentation

Calculations in Chemistry:

- By
**isha** - Follow User

- 111 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Calculations in Chemistry:' - isha

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

### Calculations in Chemistry:

Average Atomic Mass

Isotopes

- An element can exist in a number of forms, called isotopes. Isotopes are forms of the same atom that vary in mass as a result of a different number of neutrons.

- For example, there are two different types (isotopes) of copper atoms. One type of copper atoms weighs in at 62.93 amu, the other has a mass of 64.94 amu.
- These two isotopes have different proportions in a natural sample of copper.
- The lighter isotope is more common with 69.09% of the naturally occurring copper having a mass of 62.93 amu per atom.
- What is the percent abundance of the other isotope?

- The remainder of the atoms, 30.91 %, have a mass of 64.94 copper atoms. One type of copper atoms weighs in at amu.

Average Atomic Mass copper atoms. One type of copper atoms weighs in at

- To find the AVERAGE ATOMIC MASS of an atom, we take into account all of the isotopes that exist and the percentage of each type.
- The calculation of the average atomic mass is a WEIGHTED AVERAGE.

Calculation of Average Mass copper atoms. One type of copper atoms weighs in at

Average atomic mass =

Σ (mass of isotope × relative abundance)

Σ = sum or to add them all together

Calculation of Average Mass copper atoms. One type of copper atoms weighs in at

- The bottom line is that to find the average atomic mass of copper, we insert the information about copper’s isotopes into the formula and solve.
- There are two isotopes, so we will be adding the contributions of 2 isotopes. (That’s where the Σ sign comes in. )
- The relative abundance is simply the percentage of the isotope, but in decimal format. 69.09% corresponds to a relative abundance of 0.6909.

Calculation of Average Mass copper atoms. One type of copper atoms weighs in at

Average atomic mass of copper =

(62.93 amu × 0.6909)

[the mass and abundance of isotope #1]

+

(64.94 amu × 0.3091)

[the mass and abundance of isotope #2]

=

63.55

Calculation of Average Mass copper atoms. One type of copper atoms weighs in at

- From the calculation, we know that an AVERAGE atom of copper has a mass of 63.55 amu.
- Notice that in this problem, we would predict that the average is closer to the weight of the lighter isotope.
- This is because the lighter form of copper is more abundant.

Practice copper atoms. One type of copper atoms weighs in at

Check Your Answers copper atoms. One type of copper atoms weighs in at

- Silver = 107.87 amu
- Silicon = 28.09 amu
- Iron = 55.84 amu

Homework copper atoms. One type of copper atoms weighs in at

- Read section 1.4 in the text to support what we did in class today.
- pg27 #1
- Pg 29 #1-5,9

Download Presentation

Connecting to Server..