UNIT 9: Matter-1
• Matter is anything that occupies space and has mass.
Classification of Matter
• A mixture has a variable composition, whereas a substance has a fixed or definite composition.
• Two containers of pure water may have different amounts of water, but the water is composed
of hydrogen and oxygen in a fixed ratio by weight.
• A substance has one set of properties--characteristics that describe the material.
• A mixture has properties that depend on relative amounts of its components.
• Water is a substance.
• Water freezes at zero degrees Celsius.
• At normal pressure, water boils at one hundred degrees Celsius.
• Sugar water is a mixture.
• The freezing point of sugar water depends on the ratio of sugar in water.
• The boiling point of sugar water also depends of the ratio.
• A mixture may be homogeneous or it may be nonhomogeneous.
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• A mixture of salt and sugar may look homogeneous, but if you begin tasting the individual
crystals some will be sweet and others salty.
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• A substance has a definite composition and a set of properties, so any sample of a substance is
homogeneous.
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• A substance may be either a compound or an element.
• A compound can be decomposed into simpler substances.
• An element can not be decomposed into simpler substances.
Compounds
• Compounds are composed of two or more elements that are chemically combined in definite
proportions.
• Two broad classes of compounds are inorganic and organic.
• Organic compounds contain carbon as a major component.
• Inorganic compounds are the non-carbon compounds.
• Originally organic compounds were defined as those produced by living organisms, but now
there are many man-made organic compounds. We now think of most carbon compounds as
organic.
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Elements
• Elements are the basic substances.
• An element is either a metal or a non-metal.
• There are about 100 known elements and each is represented by a symbol.
• The symbol of an element is composed of one or two letters, the first is uppercase. If there is a
second letter, it is lowercase.
• The symbols for several of the elements were derived from non-English names, so they may be
a little harder to remember.
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• In general metals are
• Good conductors of heat and electricity.
• Malleable
• Ductile
• In general solid non-metals are
• Poor conductors of heat and electricity (insulators).
• Hard
• Brittle
• Two elements are liquid at room temperature (mercury and bromine).
• Eleven elements are gases at room temperature.
• The other elements are solids at room temperature.
Law of Conservation of Matter
• Matter is neither created nor destroyed in a chemical reaction.
Law of Definite Composition
• Each compound has a fixed weight ratio of its component elements.
• Near the beginning of the nineteenth century, John Dalton formulate what we now call Dalton’s
Atomic Theory.
Dalton’s Atomic Theory
• All matter is composed of tiny, indestructible particle called atoms.
• The atoms of any one element are identical, in other words, they have the mass, size and shape.
• The atoms of different elements are different.
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• Compounds are formed from atoms of two or more elements combining in small, whole
number ratios.
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• A chemical reaction involve a rearrangement of atoms; atoms are not created or destroyed.
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• The theory explains the law of conservation of matter by assuming that all matter is composed
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of indivisible, indestructible particles.
• The law of definite proportions is explained by assuming that all atoms of a given element are
alike and they are different from atoms of any other element.
• And a compound is composed of atoms of different elements in fixed number ratios.
• Therefore, a compound has a fixed mass ratio of the elements that are in it.
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• The theory allowed Dalton to formulate a new law: the law of multiple proportions.
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• Atomic Weights
• Combining ratios - valances
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