Elements are pure substances that can not be broken down into simpler substances.Ex. Calcium, Hydrogen, Fluorine

A pure substance is one that contains only one type of particle.Ex. Sugar contains only sugar particles

Compounds are pure substances that contain two or more different elements in a fixed proportion or ratio.Ex. H2O contains only hydrogen and oxygen atoms - 2 hydrogen atoms for every one oxygen atom

A molecule contains two or more atoms joined together.

The atoms may all be the same - Ex. O2 is an oxygen molecule with two

oxygen atoms joined together. The atoms may be different- Ex. CH4 (methane) or CH3COOH

(vinegar)

Proportion is important!Sugar, C12H22O11 also contains C, H and O (like vinegar) but the proportion is different

Chemical FormulasThe chemical formula is a combination of chemical symbols that represents a compound.

It tells us what elements are present and in what proportion or ratio.

The subscripts in the formula tell us how many atoms of a particular element are present in the compound.

Examples

Sugar - C12H22O11 Vinegar - CH3COOH - 12 carbon atoms - 2 carbon atoms- 22 hydrogen atoms - 4 hydrogen atoms- 11 oxygen atoms - 2 oxygen atoms

Ratio = 12C:22H:11O Ratio = 2C:4H:2O

Same elements but in a different proportion!

Now You Try!Sodium bicarbonate (baking soda!) – NaHCO3

Now You Try More!

Calcium phosphate (fertilizer) – Ca3(PO4)2

…and more!

Text book : page 47 # 3 and 4page 59 # 3, 4 and 5

Worksheet