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!

Do Now DiscussionWhy are atoms neutral in charge?Protons and electrons have

opposite chargesAtoms have the same number of

protons and electronsThe charges cancel each other

out!

Atomic Structure: Mass Number

10/22/09HAPPY THURSDAY!

Agenda:1. Cornell Notes (short!!)

2. Tic-Tac-Toe Practice3. Atom Brochures

What we’ve learned3 subatomic particles

◦Proton◦Neutron◦Electron

Atoms are neutral because# protons = # electrons

Atomic number = # of protons which determines the type of element

Mass NumberThe number of protons and

neutrons in an atom

Mass number = protons + neutrons

-or-protons = mass number - neutrons

-or-neutrons = mass number - protons

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

Examples: Calculating the Number of ProtonsIf 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!

Examples: Calculating the Number of NeutronsAn 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!

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 = 33 protons + 3 electrons = 6 charged

particles!

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 particlesF has 9 + 9 = 18 charged particlesKF has 38 + 18 = 56 charged particles!

Tic-Tac-Toe PracticeOn 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:1 2 3

4 5 6

7 8 9

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