1. ELECTRONS

2. Review Electrons were discovered by ______________ Electrons have a ___________ charge Electrons are located…. Outside of the nucleus in an electron cloud

3. Objectives Learn how to determine the charge of an atom Learn the difference between atomic number, atomic mass number, and atomic mass

4. Atomic number Atomic number = the number of protons in an atom The atomic number is always a whole number – you can never have “part” of a proton Atomic Number

5. What is the atomic number for Sodium, Oxygen, and Gold?

6. How many protons does Sodium, Oxygen, and Gold have?

7. Determining the number of Electrons The number of electrons is the same as the number of protons for neutral atoms Neutral Atom # of protons = # of electrons

8. How many electrons does Sodium, Oxygen, and Gold have? Assume they are all neutral.

9. Atomic Mass Number The atomic mass number is equal to the sum of protons and neutrons Atomic Mass Number = Protons + Neutrons

10. Determine the mass number for the following atoms. Oxygen has 8 protons, 12 electrons, and 8 neutrons Hydrogen has 1 proton, 0 electrons, and 1 neutron Carbon has 6 neutrons.

11. Solve the following problems Helium (He) is a neutral atom. How many electrons does it have? Nitrogen (N) has 9 neutrons. How many protons does it have and what is its atomic mass number? Aluminum (Al) is a neutral atom with an atomic mass number of 27. How many electrons, protons, and neutrons does it have? 2 Protons = 7 Atomic Mass Number = 16 Electrons = 13 Protons = 13Neutrons = 14

12. The number of protons classifies what type of element the atom is. Example Carbon always has 6 protons If any atom has 8 protons, what element is it?

13. The number of neutrons and electrons change from atom to atom Example Carbon can have 6 neutrons, 7 neutrons, or 8 neutrons Carbon can also have 6 electrons, 7 electrons, or 8 electrons

14. Ions Atoms that are not neutral are called ions All ions have a charge Example If carbon has 6 protons and 7 electrons, it is an ion.

15. Isotopes Atoms with the same number of protons but different number of neutrons are called isotopes.

16. The difference between Atomic Mass and Atomic Mass Number The atomic mass of an atom is the average mass of all the different isotopes for that element