Chemistry October 29/09

Atoms and Molecules

For monotomic elements: a molecule=an atom
For diatomic elements: a molecule Cl2 an atom CL

Molecules of Compounds

O

H H =H2O

2H atoms
1O atom

= 1 molecule

Ammonium Carbonate: NH3 + CO3= (NH4)2 CO3=14 atoms
Converting moles to molecules and vice versa:

6.02x10^23 molecules/1mole
OR
1mol/6.02x10^23 molecules

Examples:
How many molecules are in a 0.25 mol sample of CO2?
0.25 mol x 6.02x10^23 molecules/1mol = 1.51x10^23 molecules

There are 1.51x10^23 carbon atoms
and there are 3.02x10^23 oxygen atoms because its O(2)

5.1772x10^24 molecules of water = ? moles
5.1772x10^24 molecules x 1 mole/6.02x10^23 = 8.6 mol

Another example:
Find the number of 'H' atoms in 4.0 mol of ammonia.
NH3 convert: mol → molecules → atoms

4.0 mol x 6.02x10^23/1mol = 24.0x10^23 molecules
= 3(24.0x10^23)
= 7.22x10^24 H atoms

If you still don't get this here is a website that can help you:
http://www.chem1.com/acad/webtext/intro/MOL.html

Here's a video showing how to convert moles to atoms: