1. The Mighty Electron

2. Charges Remember, –protons always have a positive charge –electrons always have a negative charge

3. Neutral Atoms vs. Ions When an atom is neutral it means that it has an equal number of protons and electrons.. A neutral atom of boron would have 5 protons, so it would have 5 electrons. (Neutrons don’t effect the charge.)

4. Ions have an uneven number of protons and electrons. This gives them a charge. If it has more protons, it’s a positive charge, more electrons is a negative charge. This atom of oxygen has 8 protons and 10 electrons, giving it a -2 charge!

5. To find the number of electrons and protons: –Look at the symbol. If there is a little plus or minus sign, its an ion! If there is no sign, its neutral. P = neutral atom of phosphorous O -2 = ion of oxygen w/a -2 charge Li + = ion of lithium w/a +1 charge

6. Find the atomic number. This is ALWAYS the number of protons –All that can change is the number of electrons. –So F - has 1 extra electron. Fluorine’s atomic number is 9, so this ion has 9 protons and 10 electrons. 9 proton s

7. –Ca +2 is missing two electrons (more protons gives it a positive charge) Calcium’s atomic number is 20, so it has 20 protons and 18 electrons. –Ar is neutral (no + or -), so it has an equal number of protons and electrons Argon’s atomic number is 18, so it has 18 protons and 18 electrons.

8. To Find Neutrons The atomic mass is the average number of protons plus neutrons, so we need to round it. –So atomic mass (rounded) minus atomic number is the average number of neutrons. Ex. Chlorine –Mass = 35.453 »Round it to 35 –Atomic number = 17 35 – 17 = 18 Chlorine has 18 neutrons on average.

9. ElementFF-NaNa+S-2As-3KrK+ Atomic # Atomic mass # protons # electrons # neutrons

10. Find protons electrons, and neutrons for each of these: ElementProtonsElectronsNeutrons S -2 Na + As -3 Kr Fe +2

11. Bohr Models Named after Neils Bohr - discovered much of the structure of the atom.

12. First, find out the number of protons and electrons. Then fill in the shells of the model from the center outward. –The first shell can hold 2, the next 8, and the third 8 as well. P + = N 0 = Holds 8 Holds 2 Write number of protons and neutrons in the nucleus

13. Ex. –C has an atomic number of 6, so it has 6 protons and 6 electrons (if its neutral!) as well as an average of 6 neutrons. P + = 6 N 0 =6 1. First, put the number of protons (6) and neutrons (12-6=6) in the nucleus 2. Then, add electrons, starting with 2 in the inner shell. 3. Finally, add electrons to the next shell (maximum of 8) until you have added them all!

14. P + =16 N 0 =16 S -2 e- = (16+2) = 18 …2 in the inner shell, Protons = 16 Neutrons = 32-16=16 8 in next shell (it can only hold 8!) …and finally, 8 in the last shell!

15. Valence Electrons The electrons in the outermost shell of an atom are called valence electrons. –These are VERY important! They determine how (and if) the atom will bond to other atoms. P + = N 0 = Valence Electrons