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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