Download Do Now: (5 min) - Schurz High School

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 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!
Atomic Structure: Mass Number
10/22/09
HAPPY THURSDAY!
Agenda:
1. Cornell Notes (short!!)
2. Tic-Tac-Toe Practice
3. Atom Brochures
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

Mass Number
The number of protons and neutrons in an
atom
Mass number = protons + neutrons
-orprotons = mass number - neutrons
-orneutrons = 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 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!
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!
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!
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!
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:
1
2
3
4
5
6
7
8
9
Tic-Tac-Toe Practice







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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