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Scientists have developed a worldwide system for communicating chemical formulas to other scientists. This system uses the symbols for the elements off of the periodic table and a few basic rules. Read the following information and then answer both sets of practice problems.
H2O has 2 Hydrogen atoms and 1 Oxygen atom
Rule 1: Every new capital is a new element
Rule 2: The little number after a chemical symbol only applies to the symbol before it.
Rule 3: If a symbol does not have a number after it, it is assumed to be a one.
CO2 has 1 Carbon atom and 2 Oxygen atoms (not 2 Cobalt atoms)
Practice: write the number of atoms for each element in the following compounds. Use your periodic table for help with the symbols. Ex. C2O5 has 2 Carbon and 5 Oxygen.
1) O2 - 3) CO2 - 5) K2Na23F4Au5 -
2) C6H12O16 - 4) N2O - 6) MgCl2 -
Coefficients
Rule 4: A number in front of an equation applies to all numbers in the compound.
2KCl has 2 Potassium atoms and 2 Chlorine atoms
2H2O has 4 Hydrogen atoms and 2 Oxygen atoms
Parenthesis
Rule 5: A number outside the parenthesis applies to all elements inside the parenthesis
Ca (NO3) 2 has 1 Calcium atom, 2 Nitrogen atoms, and 6 Oxygen atoms
Practice: write the number of atoms for each element in the following compounds. Use your periodic table for help with the symbols.
1) 2CaO3 - 3) 3H2O - 5) Mg (OH) 2 -
2) 3KCl - 4) 2O2 - 6) Al2 (SO4) 3 -
Writing equations
Ex. When you burn charcoal, the carbon in the charcoal reacts with the oxygen in the air to create Carbon dioxide. Here is the easier way to write this:
C + O2 -> CO2 "->" means "equals" or "produces"
Reactants -> Products
Balancing equations
What is wrong with this equation? 4 + 2 = 7 - 3
Both sides must be balanced (4 + 2 = 7 - 1)
Chemical equations must be balanced, too.
H2 + O2 -> H2O is not balanced:
2 Hydrogen atoms + 2 Oxygen atoms = 2 Hydrogen atoms and 1 Oxygen atom
First you can balance it out by giving it two Oxygen atoms:
H2 + O2 -> 2H2O
Now it has four hydrogen atoms on the right side, so balance it by adding a 2 to the hydrogen
2H2 + O2 -> 2H2O
4 Hydrogen atoms + 2 Oxygen atoms = 4 Hydrogen atoms and 2 Oxygen atoms
Note: you can only balance equations by adding a coefficient (a big number in front)
Is this equation balanced?
F2 + 2KCl -> 2KF + Cl2
Yes - 2 F, 2 K, 2 Cl and 2K, 2F, and 2Cl
Practice: balance the flowing equations
1) Fe + O2 -> Fe2O4 (answer: 2Fe + 2O2 -> Fe2O4) 2) Al + Cl2 -> AlCl4
3) HCl + Na2S -> H2S + NaCl 4) Al + CuSO4 -> Al2 (SO4)3 + Cu
Look here for a good web site on writing equations
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