Compounds

Compound: a substance made up of atoms of different elements joined together (involves a chemical change) a substance made up of atoms of different elements joined together (involves a chemical change)

Example: *There is no atom of water. *There is no atom of water. *Two atoms of hydrogen join with one atom of oxygen. (chemical bond) *Two atoms of hydrogen join with one atom of oxygen. (chemical bond) *The smallest unit of water is called a molecule. *The smallest unit of water is called a molecule.

Chemical Formula: the arrangement of symbols and numbers that describe a compound the arrangement of symbols and numbers that describe a compound

Example: H 2 O H 2 O H = Hydrogen H = Hydrogen How many atoms of hydrogen? How many atoms of hydrogen? 2 atoms of hydrogen

O = Oxygen If there is no number behind the element symbol, there is just one atom of that element.If there is no number behind the element symbol, there is just one atom of that element. Therefore, there is only 1 atom of oxygen in H 2 0.Therefore, there is only 1 atom of oxygen in H 2 0.

NaCl How many elements? How many elements? 2 Name of elements Name of elements Sodium, chlorine Atoms of each element Atoms of each element Na = 1 Cl = 1 Total # of atoms Total # of atoms2 Name of compound Name of compound Table Salt

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Other Chemical Formulas

one atom of nitrogen one atom of nitrogen two atoms of oxygen two atoms of oxygen NO 2 nitrogen dioxide

aluminum oxide two atoms of aluminum two atoms of aluminum three atoms of oxygen three atoms of oxygen Al 2 O 3

acetylene two atoms of carbon two atoms of carbon two atoms of hydrogen two atoms of hydrogen C2H2C2H2C2H2C2H2

sodium carbonate two atoms of sodium two atoms of sodium one atom of carbon one atom of carbon three atoms of oxygen three atoms of oxygen Na 2 CO 3

glucose six atoms of carbon six atoms of carbon twelve atoms of hydrogen twelve atoms of hydrogen six atoms of oxygen six atoms of oxygen C 6 H 12 O 6

ammonia one atom of nitrogen one atom of nitrogen three atoms of hydrogen three atoms of hydrogen NH 3

benzene six atoms of carbon six atoms of carbon six atoms of hydrogen six atoms of hydrogen C6H6C6H6C6H6C6H6

Recipes for Compound Molecules

Write the following as a formula: # 1. hydrogen peroxide two atoms of hydrogen, two atoms of oxygen two atoms of hydrogen, two atoms of oxygen H2O2H2O2H2O2H2O2

Here are some formulas. You write out the recipe.

# 1. aluminum phosphate AlPO 4 one atom of aluminum one atom of aluminum one atom of phosphorus one atom of phosphorus four atoms of oxygen four atoms of oxygen

Do you know how to read formulas? Read through the following formulas for molecules of different compounds. Then tell how many different elements and atoms are in each molecule.

# 4. Fe 2 O 3 # of elements # of elements2 # of atoms # of atoms 5 common name common namerust

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