1. 2-3 Notation Systems for Protons, Neutrons, and Electrons (Section 4

2. If no number is written for the overall charge, then the charge is assumed to be zero; that is, there are equal number of protons (+) and electrons (-).

3. Atoms may be either electrically neutral, meaning no charge, positive (+), or negative (-). An atom with a positive or negative charge is called an ion.
 Ions are formed when atoms gain or lose electrons (remember, electrons have a -1 charge). not by changing the # of protons!!!!
If an atom gains 1 electron, it has a -1 charge. If it gains 2 electrons, it has a -2 charge. If an atom loses an electron, it has a +1 charge; loss of 2 e- yields a +2 charge.

4. Practice: #P+, n0, e- 11 27 +3 14 -3 B Al N 5 13 7 Protons: 5 13 7
B Al N
Protons:
Neutrons:
Electrons:

5. A second notation system
He – 4 is the same as 42He
The atomic number 2 is unique to the element He and doesn’t need to be written!!!
No other element has exactly 2 protons, see for yourself!!!

6. More practice: notation, #P+, no, e-
C – C – C – 14
126C C C
#P+ :
nO :
e- :

7. Difference between Mass # and Atomic weight (avg. atomic mass)
Mass # is always a whole number, since it is the sum of the protons + neutrons. The atomic weight is the weighted average of all the element’s isotopes masses; it is a decimal due to the mathematical average. It is what you see on the periodic table!
The closest whole number to the atomic mass is the most common isotope of the element.
Examples here!

8. Another wonderful practice problem just for you!
The natural abundance for boron isotopes is: 19.9% 10B ( amu) and 80.1% 11B (11.009amu). Calculate the atomic weight of boron.
What did you calculate??? 

9. You need to take into consideration:
The masses of the different isotopes and
The prevalence of those isotopes
Like this:
10B: x .199 =
11B: x .801 =
Therefore: = the avg. Atomic weight

10. Demo’s

11. 2-4 Mass Spectrometer

12. A Mass Spectrophotometer separates isotopes and gives the relative abundance of each isotope (the %). Electron beam ionizes the atoms and the + cations are accelerated into the magnetic field. The lightest masses are deflected through a greater angle than heavier masses (assuming the atoms all have the same charge).
Think about a light car and a heavy truck both taking a curve at a high rate of speed. Who will need to take the wider turn????