How to Count Atoms

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# How to Count Atoms - PowerPoint PPT Presentation

How to Count Atoms. Coefficient. If an element or molecule has a LARGE number (called a coefficient) in front of it, this is how many of each atom there are. The LARGE number (coefficient) applies to every element that follows. Example: 4 Na – FOUR Sodium atoms

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## PowerPoint Slideshow about 'How to Count Atoms' - heaton

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Presentation Transcript

### How to Count Atoms

Coefficient
• If an element or molecule has a LARGE number (called a coefficient) in front of it, this is how many of each atom there are.
• The LARGE number (coefficient) applies to every element that follows.
• Example:

4Na –FOUR Sodium atoms

2HCl –TWO Hydrogen atoms and

TWO Chlorine atoms

Subscript
• If an element has a small number directly after it, this is how many of that particular atom there are.
• Example

H2O – TWO Hydrogen atoms and

ONE Oxygen atom

C2H4 – TWO Carbon atoms and

FOUR Hydrogen atoms

REMEMBER
• IF AN ATOM DOES NOT HAVE A NUMBER IN FRONT OR BEHIND, IT IS ALWAYS

ONE

Putting the Two Together
• If you have coefficients AND subscripts, multiply the coefficient by the subscript.
• Example:

2MnO4 –TWO Manganese atoms and

EIGHT(2 x 4) Oxygen atoms

3HPO4 –THREE Hydrogen atoms and

THREE Phosphorous atoms and

TWELVE(3 x 4) Oxygen atoms

Brackets
• If there are brackets within your molecule...
• A) The coefficient STILL applies to all atoms within the molecule
• B) a subscript still applies to the atom it DIRECTLY follows.
• C) A subscript directly OUTSIDE the bracketapplies to ALL atoms INSIDE the bracket
EXAMPLES

Al(NO3)3 –ONE Aluminum atom,

THREE Nitrogen atoms (1 x 3), and

NINE Oxygen atoms (3 x 3)

3Au2(SeO4)3 –SIX Gold atoms (3 x 2),

NINE Selenium atoms (3 x 3), and

THIRTY-SIX Oxygen atoms (3 x 4 x 3).