## Tuesday, April 19, 2011

### A Little Review and Some New Calculations To Feed Your Inner Chemist.

Remember the parts of the atom facts you learned A LONG TIME AGO!?!?!
Well, dig it all back out from the back of your brain.
Just kidding, I'll just do a brief review with y'all.

There are THREE subatomic particles: Protons (p), Neutrons (n), and Electrons (e-).
p and n are located in the nucleus and have about the same mass (ie. relative mass of 1)
e- has a very small relative mass of around 0 and is located in a cloud around the nucleus.

**Remember in a neutral atoms: #p = #e-  AND that an element's atomic # is also the # of p.

Ions occur when atoms gain or lose electrons during chemical bonding.
**Remember in ions: #e- = #p - ionic charge.

Negatively charged anions gain electrons (non-metals)
Positively charged cations lose electrons (metals)

What is the difference between atomic mass and mass number?
Though they both are acquired by adding the # of protons and neutrons, atomic mass is the mass that has the trailing decimals, while the mass number is a rounded mass.

Now you try:
How many protons, neutrons and electrons are in:
1) Strontium +2
2) Sulphur
3) Neon

Then...what are isotopes?
These are just variations of an element, and usually, they are the more dangerous types.
Remember isotopes are written including their mass number! (This differentiates isotopes from isotopes)
Isotopes have the same # of protons and electrons or is normal atom, BUT DIFFERENT NEUTRONS!!
ie. heavier atomic mass

Now, the NEW stuff steps in.
We're going to learn how to calculate the NATURAL MIXTURE OF ISOTOPES.
How do we know there are a few isotopes that are present? A mystical being came riding down from the sky and told this withered old man, of course.
NO, that is definitely NOT what happened.

Some fun with radioactive isotopes.

It's really simple, actually.
The decimals in the atomic mass signify an AVERAGE.
EUREKA, right?

Let's do a question together.
Given this information, calculate the average molar mass of Fluorine.

F-18: 36.89%
F-19: 14.73%
F-20: 9.06%
F-21: 39.32%

OK. First, we'll have to convert all of the percents into decimal numbers.
Then, multiply each isotope percentage to its respective atomic mass.

F-18: (0.3689)(18g/mol)= 6.6402g/mol
F-19: (0.1473)(19g/mol)= 2.7987g/mol
F-21: (0.0906)(20g/mol)= 1.812g/mol
F-21: (0.3932)(21g/mol)= 8.2572g/mol

Finally, the last step is to add all those masses together.
6.6402g/mol + 2.7987g/mol + 1.812g/mol + 8.2572g/mol= 19.50g/mol
**DONT FORGET SIG FIGS!

Written by Jialynn.