1. Do Now: (5 min) Explain why atoms are neutral in charge. When you are finished, bring it up to the front within the first 5 minutes of class to get credit for your work!

2. Do Now Discussion Why are atoms neutral in charge? Protons and electrons have opposite charges Atoms have the same number of protons and electrons The charges cancel each other out!

3. Atomic Structure: Mass Number 10/22/09 HAPPY THURSDAY! Agenda: 1. Cornell Notes (short!!) 2. Tic-Tac-Toe Practice 3. Atom Brochures

4. What we’ve learned 3 subatomic particles ◦ Proton ◦ Neutron ◦ Electron Atoms are neutral because # protons = # electrons Atomic number = # of protons which determines the type of element

5. Mass Number The number of protons and neutrons in an atom Mass number = protons + neutrons -or- protons = mass number - neutrons -or- neutrons = mass number - protons

6. Examples: Calculating Mass Number If an atom has 8 protons and 4 neutrons, what is the mass number? Mass number = protons + neutrons = 8 + 4 = 12 If an atom has 7 protons as 15 neutrons, what is the mass number? Mass number = 7 + 15 = 22

7. Examples: Calculating the Number of Protons If an atom has a mass number of 20 and has 14 neutrons, how many protons does it have? Protons = mass number – neutrons = 20 – 14 = 6 protons! If an atom has a mass number of 45 and has 15 neutrons, how many protons does it have? Protons = 45 – 15 = 30 protons!

8. Examples: Calculating the Number of Neutrons An atom has a mass number of 12 and has 9 protons. How many neutrons does it have? neutrons = mass number – protons = 12 – 9 = 3 neutrons! If an atom has 31 protons and a mass number of 56, how many neutrons does it have? neutrons = 56 – 31 = 25 neutrons!

9. Calculating the number of charged particles in an atom/compound # charged particles = protons + electrons Example Problem: 1. A lithium atom (Li) has how many charged particles? Atomic Number = 3 3 protons + 3 electrons = 6 charged particles!

10. Examples: Calculating the number of charged particles A potassium (K) has an atomic number of 19. How many charged particles does it have? charged particles = electrons + protons = 19 + 19 = 38 charged particles! One formula unit of KF has how many charged particles? K has 19 + 19 = 38 charged particles F has 9 + 9 = 18 charged particles KF has 38 + 18 = 56 charged particles!

11. Tic-Tac-Toe Practice On a separate sheet of paper, draw a 3 x 3 table that takes up the entire page! And number the boxes 1 to 9 like the following picture: 123 456 789

12. Tic-Tac-Toe Practice There are 9 practice activities to choose from You will choose and complete one activity at a time from the board You will complete the activity in the designated box on your board (i.e. answers for activity 1 go in box 1) Make sure you show all your work! When you are finished with an activity, have Ms. Akagi check it off The Mission: complete three activities so that you get a Tic-Tac-Toe! You will be turning in your work at the end of class! When finished, you can use the rest of the time to finish your atom brochure