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UNIT 1.3 ATOMIC STRUCTURE

Chemistry is the study of matter and interactions.  Chemistry overlaps with many other sciences.

Below is the contents for this sub unit.  This will allow you to jump to any section you desire.  If you have taken Chemistry 1, this should all be review but it is always good to brush up on the basics (significant figures especially).

TABLE OF CONTENTS

PURE SUBSTANCE COMPOSITION

DEFINITE PROPORTIONS

EMPIRICAL AND MOLECULAR FORMULA

Science
Water

PURE SUBSTANCE COMPOSITION

Pure substance can be an atom, combination of the same element, or combination of different elements.  

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So Atoms that are stable alone are often metals like iron. 


BrINClHOF - There are several elements that form diatoms of the same element.  These are Br2, I2, N2, Cl2, H2, O2, F2.  These are all stable in diatom form on Earth.  Ozone is actually O3 and stable in the upper atomosphere.   

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Most substances are compounds that mix different elements.  These include water (H2O), Carbon Dioxide (CO2), etc.

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DEFINITE PROPORTIONS

Each compound is unique and has a definite proportion of elements.  This means a compound, like water, will always be made out of the same number of hydrogen (2) and oxygen (1) atoms.  This makes H2O.

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If you change the ratio to hydrogen 2 and oxygen 2, you get H2O2.  This is no longer water but hydrogen peroxide.  The properties change (more reactive and less stable).  

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But each compound is made out of whole number ratio of elements.  

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EMPIRICAL VS MOLECULAR FORMULA

Molecules can have 2 different types of formulas, empirical and molecular.  Let's take sugar.

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A simple sugar is C6H12O6.  This is it's molecular formula.

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An empirical formula is the simplest whole number.  So we can divide everything by 6 to get CH2O6.  That would be the empirical formula.

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Let's see a few more examples:

                    Name      Molecular Formula        Empirical Formula     

Methane                   CH4                 CH4

Ethane                       C2H6               CH3

Propane                      C3H8               C3H8

Butane                     C4H10               C2H5

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Ethene                 C2H4              CH2

Butene                  C4H8               CH2

So each compound has a unique molecular formula but some can have the same empirical formula.

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WHY does this matter?

The instrument we use to help analyze samples can output the relative amounts of each sample, giving the empirical formula.  So that is how we are able to help identify compounds.  More on this later.  

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