CompoundsChemistry Lecture #3

Elements Entangled

Element – the simplest type of pure substance

Pure substances that are made of more than one element are called

compounds.

A compound is two or more elements chemically combined.

Examples:

sugarwater

carbon dioxide

Compounds are cool!

The properties of the elements that make up a compound are often quite different than the compound itself.

 Compounds are made of

molecules. A molecule is made of two or more atoms chemically bonded together.

Chemical Formulas

Chemical Formulas are a shorthand way of representing chemical substances.

H2O = chemical formula for water

(two hydrogen atoms + 1 oxygen atom)

Water (hydrogen hydroxide)

Some more chemical formulas:

NH3 (ammonia) = 1 nitrogen atom +3 hydrogen atoms

C3H7OH (rubbing alcohol) = 3 carbons+ 7 hydrogen+ 1 oxygen + 1 hydrogen

AgNO3 (silver nitrate) = 1 silver + 1 nitrogen +

3 oxygen atoms

There are formulas that represent a molecule of an element.

Example: In nature, oxygen occurs as a molecule that contains 2 oxygen atoms bonded together.

O2 subscript indicates 2 atoms of oxygen

(H2 = hydrogen, N2 = nitrogen, F2 = fluorine, Cl2 = chlorine)

Equations

During a chemical reaction, substances are changed into new and different substances through a rearrangement of their atoms.

C + O2 CO2

This description of a chemical reaction using symbols and formulas is called a

chemical equation.