Molecules and Compounds

Compound

• Formed from 2 or more elements in a specific proportion

• When combined, new properties are created

• They contain 2 or more different elements

• Examples: H20, NaCl, CO2

Molecule

• A molecule is the smallest unit of a compound

• They are made up of 1 or more elements

• The elements can either be the same or different

• Examples: O2, O3, H2O, CO2

So…

• All compounds are molecules, BUT not all molecules are compounds.

• Why?

Chemical Formulas

• Scientists use chemical formulas to write the name of compounds

• It is a combination of numbers ( subscripts and coefficients) and symbols

• The subscript (small number) indicate how many of each atom are present

• The coefficient (larger number) indicate how many of each molecule is present

Example

• C3H8O is the chemical formula for rubbing alcohol.

• There are ___carbon, ___ hydrogen, and 1 oxygen atom that make up one molecule of alcohol.

Example

• NaCl is the chemical formula for salt

• There is ____ Na atom and ____ Cl atom

Example

• NH3 is the chemical formula for ammonia

• There is ____ N atom and _____ H atoms

Example

• 4CO2

• How many C and how many O?

Example Cont.

• Think about it like a math problem- 4 X (CO2)

• So there are ____ C atoms and ____ O atoms

Example

• 6H2O

• There are ___ H atoms and ____ O atoms

Example

• 3C6H12O6

• There are ____ C atoms, ____ H atoms, and ____ O atoms

Chemical Equations

• Chemists way of showing a chemical reaction with elements

• Reactant yields the product

• The arrow means “yields”

• Must be balanced (must have the same number of elements on both sides)

Chemical Equations

Chemical Equations

Chemical Equations

• Important thing to remember is the law of conservation of matter

• If there are 4 carbons on one side, there must be 4 on the other side because matter can not be created or destroyed