2. Atom Notes Notebook 3-4 10/22/02

3. What is in an atom? The Three Primary Subatomic Particles... n Protons n Neutrons n Electrons

4. Which Particle is Where? n Nucleus Protons Neutrons n Electron clouds –Swarm around the nucleus –Not in nice clear orbitals as seen in this picture

5. Protons n # of protons = the atomic number n Atomic number = # of protons n # of protons determines which element it is! n Who is element # 15? n How many protons does lithium have? n What is the atomic number of tin?

6. Atomic Number

7. Neutrons n Number of neutrons can vary, even for the same element. n Isotopes –same # of protons –different # of neutrons n Elements have many different isotopes –Carbon-14, Uranium-238 n Neutrons affect the atomic mass

8. Atomic Mass n Sum of the protons and neutrons n Electrons are not included –Too small n What is the atomic mass of this atom?

9. What about the electrons? n A neutral atom has no charge. n positive charges = negative charges. n A neutral atom has the same # of electrons as protons n How many electrons does this atom have?

10. What if the atom isn’t neutral? n If an atom is not neutral, then it has a charge. n Ion –Charge particle n This atom has: 3 protons (+++) 2 electrons (--) n It is written as Li +

11. Your Periodic Table has the answers n How many protons? n How many neutrons? n How many electrons (if the atom is neutral?)

12. SUMMING UP… n How many protons? –The atomic number n How many neutrons? –Atomic mass minus atomic number n How many electrons (if the atom is neutral?) –Same as # of protons

13. Make sure you have these definitions in your notes!! n Ion: n Isotope: n Atomic number: n Atomic mass: