Elements are pure substances that can not bebroken down into simpler substances.
Ex. Calcium, Hydrogen, Fluorine
A pure substance is one that contains only one typeof particle.
Ex. Sugar contains only sugar particles
Compounds are pure substances that contain two ormore different elements in a fixed proportion orratio.
Ex. H2O contains only hydrogen and oxygen atoms
- 2 hydrogen atoms for every one oxygen atom
A molecule contains two or more atoms joinedtogether.
The atoms may all be the same
-Ex. O2 is an oxygen molecule with two oxygenatoms joined together.
The atoms may be different
-Ex. CH4 (methane) or CH3COOH (vinegar)
Proportion is important!
Sugar, C12H22O11 also contains C, H and O (likevinegar) but the proportion is different
Chemical Formulas
The chemical formula is a combination of chemicalsymbols that represents a compound.
It tells us what elements are present and in whatproportion or ratio.
The subscripts in the formula tell us how manyatoms of a particular element are present in thecompound.
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 4
page 59 # 3, 4 and 5
Worksheet