Chapter 2 Matter
CHAPTER OUTLINE
Section 1 Classifying Matter
Key Idea questions
> How can matter be classified?
> Why are carbon and copper classified as elements?
> How are elements related to compounds?
> What is the difference between a pure substance and a mixture?
What is Matter?
> How can matter be classified?
> Every sample of matter is either an element, a compound, or a mixture.
• matter: anything that has mass and takes up space
Elements
> Why are carbon and copper classified as elements?
> Each element is made of one kind of atom.
• element: a substance that cannot be separated or broken down into
simpler substances by chemical means
• atom: the smallest unit of an element that maintains the properties of
that element
• Elements are represented by symbols.
• Atoms that make up a molecule act as a unit.
• molecule: the smallest particle of a substance that has all of the
chemical properties of that substance; a molecule is made up of one
atom or two or more atoms bonded together
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Chapter 2 Matter
Compounds
> How are elements related to compounds?
> Each molecule of a compound contains two or more elements that are
chemically combined. Elements combine chemically to form a
compound.
• compound: a substance made up of atoms of two or more different
elements joined by chemical bonds
• Compounds have unique properties.
• Chemical formulas represent compounds.
–
The following chemical formula represents the compound for
indigo: C16H10N2O2
Pure Substances and Mixtures
> What is the difference between a pure substance and a mixture?
> Elements and compounds are pure substances, but mixtures are not.
• pure substance: a sample of matter, either a single element or a
single compound, that has definite chemical and physical properties
• mixture: a combination of two or more substances that are not
chemically combined
• Mixtures are classified by how thoroughly the substances mix.
–
heterogeneous mixture: substances aren’t mixed uniformly and
are not evenly distributed
–
homogeneous mixture: substances are evenly distributed, and the
mixture is the same throughout
–
miscible: substances that can be mixed
–
immiscible: substances that cannot be mixed
• Gases can mix with liquids.
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Chapter 2 Matter
Section 2 Properties of Matter
Key Idea questions
> Why are color, volume, and density classified as physical properties?
> Why are flammability and reactivity classified as chemical properties?
Physical Properties
> Why are color, volume, and density classified as physical properties?
> Physical properties are characteristics that can be observed without
changing the identity of the substance.
• Physical properties can help identify substances.
• Physical properties can be observed or measured.
– Examples: shape, color, odor, texture, state, melting point, boiling
point, strength, hardness, magnetism, the ability to conduct
electricity or heat
– melting point: the temperature and pressure at which a solid
becomes a liquid
– boiling point: the temperature and pressure at which a liquid
becomes a gas
• Physical properties help determine uses.
• Density is a physical property.
– density: the ratio of the mass of a substance to the volume of the
substance
– common unit of density is g/cm3
• Density is different from weight.
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Chapter 2 Matter
Chemical Properties
> Why are flammability and reactivity classified as chemical properties?
> A chemical property describes how a substance changes into a new
substance, either by combining with other elements or by breaking
apart into new substances.
• Flammability is a chemical property.
– flammability: the ability to burn
• Reactivity is a chemical property.
– reactivity: the capacity of a substance to combine chemically with
another substance
• Physical and chemical properties are different.
– Physical properties can be observed without changing the identity
of a substance.
– Chemical properties can be observed only in situations in which
the identity of the substance changes.
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Chapter 2 Matter
Section 3 Changes of Matter
Key Idea questions
> Why is getting a haircut an example of a physical change?
> Why is baking bread an example of a chemical change?
> How can mixtures and compounds be broken down?
Physical Changes
> Why is getting a haircut an example of a physical change?
> A physical change affects one or more properties of a substance
without changing the identity of the substance.
• physical change: a change of matter from one form to another
without a change in chemical properties
• Physical changes do not change a substance’s identity.
– Examples of physical changes: cutting, crushing, reshaping,
changing state
• Dissolving is a physical change.
Chemical Changes
> Why is baking bread an example of a chemical change?
> A chemical change happens when one or more substances are
changed into entirely new substances that have different properties.
•
chemical change: a change that occurs when one or more
substances change into entirely new substances with different
properties
•
Chemical changes happen everywhere.
–
•
Examples of chemical changes: burning, rusting, digesting,
decomposing
Chemical changes form new substances.
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Chapter 2 Matter
•
Chemical changes can be detected.
–
•
Signs include: change of color, change of smell, fizzing,
production of heat, production of sound, production of light
Chemical changes cannot be reversed by physical changes.
Breaking Down Mixtures and Compounds
> How can mixtures and compounds be broken down?
> Mixtures can be separated by physical changes, but compounds must
be broken down by chemical changes.
•
Mixtures can be physically separated.
•
Examples of separating a mixture:
–
Separating saltwater into its parts by heating it: When the water
evaporates, the salt remains.
–
Using a distillation device to heat a mixture whose components
have different boiling points: The component that boils and
evaporates first separates from the mixture.
–
Using a centrifuge: The mixture spins rapidly until the components
separate.
•
Some compounds can be broken down through chemical changes.
•
Examples of separating a compound:
–
When mercury(II) oxide is heated, it breaks down into the
elements mercury and oxygen.
–
When a current is passed through melted table salt, the elements
sodium and chlorine are produced.
–
When you open a bottle of soda, carbonic acid in the soda breaks
down into carbon dioxide and water.
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