counting atoms
DESCRIPTION
Learn how to count atoms.TRANSCRIPT
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COUNT ATOMHow to count atoms
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How many elements?
• Remember the symbol for an element is made up of one or two letters.
• It is easy to figure out because they are capitalized.
• HF – (Hydrofluoric acid) is made up of H (hydrogen) and F (fluor)
• NaCl (sodium chloride) is made up of Na (sodium) and Cl (chlorine)
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What about these?
• H2Se H – hydrogen and Se - selenium
• Na4O7P2
Na – sodium O - oxygen P - phosphorus
• HCl H – hydrogen Cl - Chlorine
• K2Te K – Potassium Te - Tellurium
• C232 N92O139P22C – carbon N – nitrogenO – oxygen P - phosphorus
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Subscripts
• Subscripts tell us how many atoms of the element BEFORE them there are.
H2OSUBSCRIPT
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No subscript• If there are no subscripts it means
there is only one atom of the element.
• HF – Hydrogen = 1 Fluorine = 1
• CaCl2 – Calcium = 1 Chlorine = 2
• H3PO4 – Hydrogen = 3 Phosphorus = 1
Oxygen = 4
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What about these?
• C3H4O3
C = 3 H = 4O = 3
• H2OH = 2O = 1
• C232 N92O139P22
C = 232 H = 92O = 139P = 22
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But it has a parenthesis
• Parenthesis group atoms into polyatomic ions.
• Don’t worry, the only thing you have to
do is multiply the number of atoms inside the parenthesis by the subscript outside the parenthesis.
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Say what?
• Think distributive property:
Zn (MnO4)2
Zn = 1 atomMn = 1 x 2 = 2 atoms
O = 4 x 2 = 8 atoms
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What about these:
• Fe(OH)3Fe = 1O = 1 x 3 = 3H = 1 x 3 = 3
• Sr3(PO4)2Sr = 3P = 1 x 2 = 2O = 4 x 2 = 8
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Finally the Coefficient
2H2OCOEFFICIENT SUBSCRIPT
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2H2OThe coefficient gets applied to the
ENTIRE formula
-this means that there are 2 molecules of water present!
-you MULTIPLY this number by every subscript in the formula
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2H2O
2 MOLECULES!!!!
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2H2OHow many hydrogen atoms are present?
4
How many oxygen atoms are present?
2
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Let’s try an example:
4CaCO3
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1. Write down symbols
• 4CaCO3
Ca
C
O
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Write down the coefficient next to each symbol
4CaCO3
Ca
C
O
4
4
4
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Multiply by the subscript
4CaCO3
Ca
C
O
4
4
4
X
X
X
1
1
3
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Multiply…
4CaCO3
Ca
C
O
4
4
4
X
X
X
1
1
3
=
=
=
4
4
12
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Add totals together to get the total amount of atoms
4CaCO3
Ca
C
O
4
4
4
X
X
X
1
1
3
=
=
=
4
4
1220
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Now with your table
• 3CO2
• 2C6H12O6
• 6K2SO4
• CaMg(CO3)2
• 3Pb(NO3)2