1. January 12, 2016 Today’s Schedule Today you will need Q/A
Starting Counting Atoms
Today you will need
Pen/Pencil
Paper/ Notebook

2. Q/A
Draw a Bohr Diagram for the following Elements
Hydrogen
Oxygen

3. Counting Atoms

4. Counting Atoms The symbol of an element = one atom of that element
Ex. Na= 1 Sodium atom
So how many atoms are in:
Mg=
Ni= K=

5. More than …
But when atoms make compounds (two or more elements combined) Sometimes we get more than one atom in a molecule.
Remember, atoms = letters, molecules= words
Ex: H2O
In water there is two hydrogen atoms for every one Oxygen atom

6. How do we know ?
We know because water has a subscript in its molecule.
A subscript= any number written at the lower right corner behind the symbol of an element. The subscript tells us the number of atoms.

7. H2O Oxygen doesn’t have a subscript so there is only one Oxygen atom.
2 is the subscript, so there are two hydrogen atoms

8. More than one…
When there is more than one atom in a compound, we can break it apart to tell how many there are.
Ex: Sugar C 6 H12 O 6
First we write the different elements that are in this compound.
Carbon
Hydrogen
Oxygen

9. C6H12O6 Then we match up the subscript to the element. Carbon= 6 atoms
Hydrogen= 12 atoms
Oxygen= 6 atoms

10. Try it !
Break these compounds apart into separate elements and find out how many atoms are in each.
H2CO3
C 2H6O
H2O2

11. Try it: H2CO3 C 2H6O Hydrogen= 2 atoms Carbon = 2 atoms
Carbon= 1 atom Hydrogen= 6 atoms
Oxygen= 3 atoms Oxygen= 1 atom

12. H2O2
Hydrogen= 2 atoms
Oxygen= 2 atoms

13. Sometimes… there are more
A subscript outside a bracket multiplies all the elements inside the bracket.
Ex: (H2O)3
The subscript outside the bracket shows us that there are 3 water molecules.
Subscript outside the bracket

14. (H2O)3 Now lets break it apart the same way as before
Hydrogen= 2 X 3 = 6 atoms
Oxygen= 1 X 3 = 3 atoms

15. Try it!
Mg3(PO4)2
Magnesium=
Phosphorous=
Oxygen=

16. Magnesium= 3 atoms Phosphorous= 1 X 2= 2 atoms Oxygen= 4 X 2 = 8 atoms
Mg3(PO4)2
Magnesium= 3 atoms
Phosphorous= 1 X 2= 2 atoms
Oxygen= 4 X 2 = 8 atoms

17. Q/ A
Break down the following compound to its elements and how many atoms of each element are there.
Fe3(KO4)3

18. Fe3(KO4)3
Iron= 3 atoms
Potassium= 1 X 3= 3 atoms
Oxygen= 4 X3= 12 atoms

19. And sometimes there is a coefficient
A coefficient is a number written IN FRONT of a chemical symbol and indicates the number of atoms of the element.
Ex: C
So there are 3 Carbon atoms.
Coefficient

20. So how many ?
How many atoms are in the following elements that have coefficients ?
2 Ca
2 Calcium atoms
6 Ni
6 nickle atoms

21. But what if there is more than one element ?
When a coefficient is a number written IN FRONT of a molecule, it indicates the number of molecules in that compound.
So? You have to multiply the coefficient by the number of atoms.
Ex. 3 CuSO4

22. 3 CuSO4 Break it down: Copper= 3 X 1= 3 atoms Sulfur= 3 X 1 = 3 atoms
Oxygen= 3 X 4 = 12 atoms

23. Practice
Work on the back of the how to count atoms notes for practice.