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1. Atoms, Elements, Molecules,&
Compounds
What happens when substances combine?
8.8B Identify the properties of an atom.
8.9A Demonstrate that substances may react
chemically to form new substances.

2. Atoms, Elements, Molecules,& Compounds
Substance — Matter that has the same composition and
properties throughout.
Atom means “cannot be divided” – smallest unit
of element that retains properties
Element — simplest form of substance, pure substance,
Listed on Periodic Table
 smallest unit only one kind of atom.
Molecule — two or more atoms combined
 smallest particle of a substance
 May be two atoms of one element O2 N2
 May also be two or more atoms of different
elements CO H O
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3. Compound: more than one element combined
 in definite proportion (fixed ratio)
 makes new substance different from elements.
Water: H2O Carbon Dioxide: CO2 Sugar: C6H12O6
Substances can react and form new substances.
 Changes occur during these reactions.
 List the types of Chemical Changes:
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Can you distinguish between elements and molecules?
Between molecules and compounds? Name the chemical
reactions? Write your summary.