Compounds

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

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

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

Example: H2O H = Hydrogen How many atoms of hydrogen?

O = Oxygen 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 H20.

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

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Other Chemical Formulas

nitrogen dioxide one atom of nitrogen two atoms of oxygen NO2

aluminum oxide two atoms of aluminum three atoms of oxygen Al2O3

acetylene two atoms of carbon two atoms of hydrogen C2H2

Na2CO3 sodium carbonate two atoms of sodium one atom of carbon three atoms of oxygen Na2CO3

C6H12O6 glucose six atoms of carbon twelve atoms of hydrogen six atoms of oxygen C6H12O6

ammonia one atom of nitrogen three atoms of hydrogen NH3

benzene six atoms of carbon six atoms of hydrogen C6H6

Recipes for Compound Molecules

Write the following as a formula: # 1. hydrogen peroxide two atoms of hydrogen, two atoms of oxygen H2O2

Here are some formulas. You write out the recipe.

# 1. aluminum phosphate AlPO4 one atom of aluminum one atom of phosphorus four atoms of oxygen

Do you know how to read formulas 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. Fe2O3 # of elements 2 5 # of atoms common name rust

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