1. Atomic Structure

2. Sub-Atomic Particles Nucleus – a dense, positively charged region at the center of the atom Proton p +  Positively charged particle located in the nucleus Neutron n o  Neutral particle (no-charge) located in the nucleus Electron e -  Negatively charged particle “surrounding” the nucleus

3. Sub-Atomic Particles Mass: Protons and neutrons have roughly the same mass 1 AMU. Electrons are much, MUCH smaller (in fact we usually don’t count them in mass calculations!) Charges: Protons and electrons have equal but opposite charges. Neutrons are electrically neutral.

4. Atomic Number Number of protons in an atom This is the WHOLE number next to the symbol on the periodic table. 17 Cl 35.453

5. Atomic Mass 26 Fe 55.845 Mass of atom Calculated by adding together protons and neutrons Recorded in amu (atomic mass units) This is the decimal number found next to the symbol

6. Calculating Atomic Mass 26 Fe 55.845 Atomic Mass = #protons + #neutrons Most often you will calculate the #neutrons from the information found on the periodic table #neutrons = atomic mass - #protons #neutrons = 56 – 26 #neutrons = 30 Round the decimal part

7. Average Atomic Mass Since atoms of any given element can exist in different forms (isotopes), we average together the masses of the isotopes. From this number we can infer which are the most common isotopes.

8. Isotopes Isotopes still have the same atomic number, they just have a different mass number due to the a different number of neutrons.

9. Ions Neutral atoms have equal amounts of positive and negative charge. When an atom gains or loses electrons, it will become charged, and then we call it an ion.

10. Drawing Bohr Models First, determine the number of protons, neutrons, and electrons. Draw the nucleus with the protons and neutrons. Next, determine the number of energy levels. Draw the energy levels with the correct number of electrons on each level