Chemical Equations Study Guide •
Molecules are made of atoms that have been joined together.
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There are two types of molecules: o Elements (H2) o Compound (NaCl)
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An element is when two or more of the same atoms join together. o
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Example: O2 (the oxygen we breath) is made out of two oxygen atoms.
A Compound is a combination of two or more different elements (atoms). o Example: 1 Na (sodium) atom + 1 Cl (Chlorine) atom = the compound NaCl
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The example above is a compound because the molecule is made out of different atoms.
The subscript in the below example shows that in O2 there are 2 oxygen atoms. The coefficient in 2H2O shows that there are 2 H2O water molecules.
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The 3 particles found in an atom are the proton, electron, and neutron.
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Protons have a positive charge and are found inside the nucleus.
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Electrons have a negative charge and are found outside the nucleus.
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Neutrons have no (zero) charge and are found inside the nucleus.
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The atomic massis made up of the massof both the proton and neutron.
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The first energy level can only hold 2 electrons.
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The second energy level can only hold 8 electrons.
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The third energy level can only hold 8 electrons.