elements are pure substances that can not be broken down into simpler substances. ex. calcium,...

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