representing matter
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Representing Matter
• The fundamental unit of matter is the atom.– Greek-”unbreakable”
• A neutral group of atoms held together by chemical bonds is called a molecule
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Matter cont.
• Elements are the simplest pure substances. – Contain only one kind
of atom.– Each has their own set
of physical and chemical properties
Diatomic
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Matter cont.
• If a molecule has at least two different kinds of atoms present then it is a compound
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Classifying Matter
• Use the symbols of the elements– Ag, Na, H2, NaCl, H2O, etc
• Subscripts tell how many of an atom is in the molecule– H2O, H2SO4, CaCl2
• Coefficients tell how many of the atom/molecule– Ag, 2Na, 3H2, 4NaCl, 5H2O, etc
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Pure Substances
• Fixed composition
• Cannot be separated into simpler substances by physical methods (physical changes)
• Can only be changed in identity and properties by chemical methods
• Properties do not vary
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Mixtures
• Variable composition• Components retain their
characteristic properties• May be separated into
pure substances by physical methods
• Mixtures of different compositions may have widely different properties
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Homogeneous Mixtures
• Homogenous mixtures look the same throughout but can be separated by physical means (dissolution, centrifuge, gravimetric filtering, etc.). Examples: milk, yogurt, solutions
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Heterogeneous Mixtures
• Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).