1. ATOMIC STRUCTURE

2. Current Model of Atomic Structure
Nucleus: center of atom
Very dense
Contains protons and neutrons
Electron cloud
Areas around nucleus where electrons are likely to be
Organized in levels
Close to nucleus, less energy
Each level can hold a certain number of electrons

3. The Subatomic Particles
Protons
Positive charge p+
Have mass of 1amu
amu = atomic mass unit
1/12 a Carbon 12 atom

4. The Subatomic Particles
Neutrons
No charge n0
mass of 1 amu

5. The Subatomic Particles
Electrons
Negative charge e-
very, very little mass (not counted)

6. Mass Only protons and neutrons have mass Each has a mass of 1 amu
Mass Number = protons + neutrons
Average Atomic Mass = weighted average of all isotopes of an element
More on this later
This is what is listed on the periodic table

7. Atomic Number Number of protons in an element Never changes!
If you change the number of protons you would have a different element
How does this compare to changing the number of neutrons?

8. Element Boxes
Atomic Mass
16.00 O
Chemical Symbol 8
Atomic Number

9. The boxes give lots of information…
Atomic number is the number of protons
Neutral atom (no positive or negative charge)
Protons = electrons
Use the MAN formula to get number of neutrons

10. What's the MAN Formula?!? Mass (rounded to a whole number!)
-Atomic Number
Neutrons

11. MAN example… 3 Li Lithium 6.941
Mass=6.941round to 7 Atomic Number=3 M - A = Neutrons 7 – 3 = 4 neutrons! 3 Li
Lithium
6.941

12. What else do we know? 3 Li Lithium 6.941
Atomic Number=3 -3 protons -if it is neutral (which it is unless you are told it isn’t), than there are also 3 electrons 3 Li
Lithium
6.941

13. A Note on Symbols… Capital and lower case letters are important!
Co is the metal cobalt (one of the elements that can become a magnet and is associated with the color blue in some pigments)
CO is a deadly gas!
Carbon monoxide
ALWAYS USE CAPITALS AND LOWER CASE LETTERS PROPERLY!!!

14. Isotopes Atoms of same element that have different masses
same number of protons, but different neutrons
Atomic mass is the average of the masses of the different isotopes
not even numbers
Sodium (Na) is 22.9
Depending on the context, you will either round to a whole number or use the exact number from the periodic table

15. Isotope and Symbolic Notation

16. Calculating Average Atomic Mass
Percent abundance x isotope mass = mass contribution
Add up the mass contribution of each element to get the average atomic mass
Example: Mg has 3 isotopes, calculate the average atomic mass:
78.99% is 24 amu
10.00% is 25 amu
11.01% is 26 amu