1. Mrs. Burt’s Physical Science Class
Unit 3: Chemistry
Lesson 3, 4, 5

2. Lesson 3 Chemical Formulas
Compare ionic and covalent compounds and their molecular formulas.
Identify various compounds by their chemical formulas.
Explain and give examples of how chemical formulas can express chemical reactions.

3. Lesson 3 Chemical Formulas
First, Let’s review Ionic and Covalent bonds:
Ionic bonds are formed from the attraction of two oppositely charged ions (NaCl).
A covalent bond forms when atoms share pairs of electrons (CO2).

4. Chemical Formula?
A chemical formula is a combination of symbols and numbers that how many atoms of each kind of element are in a molecule of a particular compound.
Let’s look at H2O. Who can tell me what these Letters and numbers mean?

5. Ionic Compound Formulas
Formulas tell us how many atoms are in a molecule of a compound. But, how do we know how many atoms there should be?!
All ionic compounds are electrically balanced or neutral with a charge of zero.
Remember when we looked at the charges of sodium and Chlorine in NaCl? What charge did Na have? Cl?
Is it an electrically balanced compound?

6. Let’s try some more! Hydrochloric Acid: Calcium Fluoride:
Hydrogen = H+
Chlorine= Cl-
H+ + Cl - =
(Hydrogen + Chlorine = )
Calcium Fluoride:
Calcium= Ca2+
Fluoride=F-
Ca2+ + F- =
(Calcium + Fluorine = )

7. Covalent Compound Formulas
For a covalent compound, the chemical formula shows how many atoms of each kind join together to form the molecules of the compound. Molecular Formula! (no + or – charges needed)
Instead of charges, we use prefixes

8. Prefix Table Number of Atoms Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5
penta- 6
hexa- 7
hepta- 8
octa- 9
Nona-
We have all heard of Carbon Dioxide. What is the molecular formula?
One Carbon atom and two Oxygen atoms.

9. Let’s try some Molecular Formulas!!
Sulfur Trioxide:
1 Sulfur and 3 Oxygen
Dinitrogen trioxide:
Nitrogen and Oxygen

10. Structural Formulas
Structural formulas are used to represent a covalent molecule.
Let’s look at some photos (structural formulas) and see if we can figure out their chemical formulas.
Start with Carbon atoms, then hydrogen atoms, then oxygen.

11. Butanol
What is the chemical formula?

12. Glucose
What is the chemical formula? C= H= O=
Magnesium Chloride?

13. Writing Chemical Formulas
A chemical equation shows a relationship between substances on the left (_________) and substances on the right (________) sides of the equation.
reactants products

14. Examples of Chemical Formulas

15. Terms
A polymer is a covalently bonded molecule consisting of repeating chemical units.
These units can form long chains.
Each of the repeating units is called a monomer.
The chemical formula of the monomer is simply repeated many times in the polymer.
It’s a fancy way of saying what the pic on the next slide shows:

16. Mono means single or alone. Poly means much or many. So…..many of one!

21. Thank you!