Mrs. Burt’sPhysical Science Class

Unit 3: ChemistryLesson 3, 4, 5

Lesson 3Chemical 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.

Lesson 3Chemical 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).

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?

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?

Let’s try some more!

• Hydrochloric Acid: – Hydrogen = H+– Chlorine= Cl-– H+ + Cl - =– (Hydrogen + Chlorine = )

• Calcium Fluoride:– Calcium= Ca2+– Fluoride=F-– Ca2+ + F- =– (Calcium + Fluorine = )

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

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.

Let’s try some Molecular Formulas!!

• Sulfur Trioxide:– 1 Sulfur and 3 Oxygen

• Dinitrogen trioxide:– Nitrogen and Oxygen

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.

Butanol

• What is the chemical formula?

Glucose

• What is the chemical formula?• C=• H=• O=• Magnesium Chloride?

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

Examples of Chemical Formulas

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:

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

Thank you!