Transcript Ppt Properties of Matter / Pure Substances

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Table of Contents
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Topic 1: Chemistry and Matter
Basic Concepts
Additional Concepts
Chemistry and Matter: Basic Concepts
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Composition, Structure, and Behavior
• Chemistry is the science that investigates
and explains the structure and properties of
matter.
• Matter is the stuff that’s all around you: the
metal and plastic of a telephone, the paper
and ink of a book, the glass and liquid of a
bottle of soda, the air you breathe, and the
materials that make up your body.
• A more formal definition of matter is
anything that takes up space and has mass.
Chemistry and Matter: Basic Concepts
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Composition, Structure, and Behavior
• Mass is the measure of the amount of matter
that an object contains.
• The structure of matter refers to its
composition—what matter is made of—as
well as how matter is organized.
• The properties of matter describe the
characteristics and behavior of matter,
including the changes that matter
undergoes.
Chemistry and Matter: Basic Concepts
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Macroscopic View of Matter
• Matter that is large enough to be seen is
called macroscopic, so all of your
observations in chemistry, and everywhere
else, start from this perspective.
• You may get hints of the actual structure
from a macroscopic view. You must go to a
submicroscopic perspective to understand
how the hidden structure of matter influences
its behavior.
Chemistry and Matter: Basic Concepts
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Submicroscopic View of Matter
• The submicroscopic view gives you a
glimpse into the world of atoms.
• It is a world so small that you cannot see it
even with the most powerful microscope,
hence the term submicroscopic.
• You learned in earlier science courses that
matter is made up of atoms.
Chemistry and Matter: Basic Concepts
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Using Models in Chemistry
• In your study of chemistry, you will use both
macroscopic and submicroscopic
perspectives.
• For example, sucrose and aspirin are both
composed of carbon, hydrogen, and oxygen
atoms, but they have different behaviors and
functions.
• These differences must come about because
of differences in the submicroscopic
arrangement of their atoms.
Chemistry and Matter: Basic Concepts
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Comparing the Structures of Aspirin
and Sucrose
• The different submicroscopic arrangements of
the atoms in aspirin and sucrose cause the
differences in their behavior.
aspirin
sucrose
Chemistry and Matter: Basic Concepts
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Using Models in Chemistry
• A scientific model is a
thinking device that helps
you understand and
explain macroscopic
observations. Scientific
models are built on
experimentation.
Chemistry and Matter: Basic Concepts
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Classification by Composition
A powerful way to classify matter is by its
composition. This is the broadest type of
classification.
When you examine an unknown piece of
stuff, you first ask, “What is it made of?”
Sucrose is composed of the elements carbon,
hydrogen, and oxygen. This is a qualitative
expression of composition.
A qualitative observation is one that can be
made without measurement.
Chemistry and Matter: Basic Concepts
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Classification by Composition
• After a qualitative analysis, the next question
that you might ask is how much of each of
the elements is present.
• For sucrose, the answer to that question is
that 100 g of sucrose contains 42.1 g of
carbon, 51.4 g of oxygen, and 6.5 g of
hydrogen. This is a quantitative expression of
composition.
• A quantitative observation is one that uses
measurement.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• A sample of matter is either pure—made up of
only one kind of matter—
or it is a mixture of
different kinds of matter.
• A substance is matter,
either an element or
compound, with the same
fixed composition and
properties.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• A mixture is a combination of two or more
substances in which the basic identity of each
substance is not
changed.
• Unlike pure substances,
mixtures do not have
specific compositions.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• A physical change is a change in matter that
does not involve a change in the chemical
identity of individual substances.
• Examples of physical changes include:
• boiling,
• evaporating,
• freezing,
• dissolving,
• melting,
• and crystallizing.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• Physical properties are characteristics that a
sample of matter exhibits without any change
in its identity.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• Examples of the physical properties of a
chunk of matter include its:
• solubility,
• melting point,
• boiling point,
• color,
• density,
• electrical conductivity,
• and physical state (solid, liquid, or gas).
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• A heterogeneous mixture is one with
different compositions, depending upon
where you look.
• The components of
the mixture exist as
distinct regions,
often called phases.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• Homogeneous mixtures are the same
throughout.
• Another name for a homogeneous mixture is
solution.
• Some solutions are gases. Air, for example, is
a homogeneous mixture of several gases.
• Some solutions are solid.
• Liquid solutions do not have to be liquid or
contain water.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• Alloys are solid
solutions that
contain different
metals and
sometimes
nonmetallic
substances.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• When you dissolve sugar in water, sugar is
the solute—the substance being dissolved.
• The substance that dissolves the solute, in
this case water, is the solvent.
• When the solvent is water, the solution is
called an aqueous solution.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
• Many of the solutions you
encounter are aqueous
solutions, for example, soda,
tea, contact-lens cleaner, and
other clear cleaning liquids.
• In addition, most of the
processes of life occur in
aqueous solutions.
Chemistry and Matter: Basic Concepts
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Pure substance or a mixture?
Chemistry and Matter: Basic Concepts
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Two Types of Substances
• One type of pure substance can be broken
down into simpler substances. This type of
substance is called a compound.
• Another type of substance cannot be broken
down into simpler substances. Such a
substance is called an element.
• All the substances of the universe are either
elements, compounds formed from elements,
or mixtures of elements and compounds.
Chemistry and Matter: Basic Concepts
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Two Types of Substances
• Of the known elements, only about 90 occur
naturally on Earth. The remainder are
synthesized, usually in barely detectable
amounts, in high-energy nuclear experiments.
• Less than half of the 90 naturally occurring
elements are abundant enough to play a
significant role in the chemistry of everyday
stuff.
Chemistry and Matter: Basic Concepts
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Organizing the Elements
• The periodic table organizes elements in a
way that provides a wealth of chemical
information—much more than is evident to
you now. It shows the chemical symbols for
the elements.
• Their symbols usually correspond to their
names in Latin.
Chemistry and Matter: Basic Concepts
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Periodic Table of the Elements
Chemistry and Matter: Basic Concepts
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Compounds Are More Than One Element
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• A more complete definition is that a
compound is a chemical combination of two
or more different elements joined together in a
fixed proportion with a unique set of chemical
and physical properties.
• More than 10 million compounds are known
and the number keeps growing.
Chemistry and Matter: Basic Concepts
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Compounds Are More Than One Element
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• Some new compounds are discovered and
isolated from natural chemical sources such as
plants and colonies of bacteria and are
synthesized in laboratories for many different
uses.
Chemistry and Matter: Basic Concepts
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Compounds Are More Than One Element
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• The properties of the compound are different
from the properties of the elements that
compose the compound.
silver
+
bromine = silver bromide
Chemistry and Matter: Basic Concepts
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Compounds Are More Than One Element
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• More than 10 million compounds are known
and the number keeps growing.
• New compounds are discovered and isolated
from natural chemical sources such as plants
and colonies of bacteria and are synthesized
in laboratories for many different uses.
Chemistry and Matter: Basic Concepts
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Compounds Are More Than One Element
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• A formula is a combination of the chemical
symbols that show what elements make up a
compound and the number of atoms of each
element.
Compound
Formula
Caffeine
C8H10N4O2
Chemistry and Matter: Basic Concepts
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Compounds Are More Than One Element
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• Formulas provide a shorthand way of
describing a submicroscopic view of a
compound.
• You probably already use formulas like H2O
and CO2 as a way of talking about water and
carbon dioxide.
Chemistry and Matter: Basic Concepts
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States of Matter
• Most matter on Earth exists in one of three
physical states: solid, liquid, or gas. A fourth
state of matter, called plasma, is less familiar.
• Changes in state are examples of physical
changes because there is no change in the
chemical composition identity of the
substance.
• Ice can melt back to form liquid water, and
steam will condense on a cool surface to
form liquid water.
Chemistry and Matter: Basic Concepts
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States of Matter
• Some substances are described as volatile,
which means that they change to a gas easily
at room temperature.
• Alcohol and gasoline are more volatile than
water.
• Density is the amount of matter (mass)
contained in a unit of volume.
• Styrofoam has a low density or small mass per
unit of volume.
Chemistry and Matter: Basic Concepts
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States of Matter
• Stones have a large
density or a large mass
per unit of volume.
• In science, the density of solids and liquids is
usually measured in units of grams (mass)
per milliliter (volume) or g/mL.
Chemistry and Matter: Basic Concepts
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Chemical Properties
• Chemical properties are those that can be
observed only when there is a change in the
composition of the substance.
• Rusting is a chemical reaction in which iron
combines with oxygen to form a new
substance, iron oxide.
• Inability to react is also a chemical property.
Chemistry and Matter: Basic Concepts
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Chemical Changes
• A chemical property always relates to a
chemical change, the
change of one or more
substances into other
substances.
• Another term for
chemical change is
chemical reaction.
Chemistry and Matter: Basic Concepts
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Chemical Changes
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Chemistry and Matter: Basic Concepts
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Chemical Changes
• All matter is made of atoms, and any
chemical change involves only a
rearrangement of the atoms. Atoms do not
just appear. Atoms do not just disappear.
• This is an example of the law of
conservation of mass, which says that in a
chemical change, matter is neither created
nor destroyed. It would be equally correct to
call this the law of conservation of matter.
Chemistry and Matter: Basic Concepts
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Chemical Reactions and Energy
• All chemical changes also involve some sort
of energy change.
• Energy is either taken in or given off as the
chemical change takes place. Energy is the
capacity to do work.
• Work is done whenever something is moved.
Chemistry and Matter: Basic Concepts
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Chemical Reactions and Energy
• Many reactions give off energy.
• For example, burning wood
is a chemical change in
which cellulose, and other
substances in the wood,
combine with oxygen from
the air to produce mainly
carbon dioxide and water.
Chemistry and Matter: Basic Concepts
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Chemical Reactions and Energy
• Energy is also produced and released in the
form of heat and light.
• Chemical reactions that give off heat energy
are called exothermic reactions.
• Chemical reactions that absorb heat energy
are called endothermic reactions.
Chemistry and Matter: Basic Concepts
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Chemical Reactions and Energy
• You can tell that the decomposition of water
into oxygen and hydrogen is an endothermic
reaction because it doesn’t occur unless
energy, in the form
of an electric
current, is passed
through water.
Chemistry and Matter: Basic Concepts
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Chemical Reactions and Energy
• Photosynthesis is
probably the most
important endothermic
process on Earth.
• Green plants, algae, and
many kinds of bacteria
carry out photosynthesis.
Basic Assessment Questions
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Question 1
Identify each of the following as either a
compound or a mixture.
A. sand
B. water
C. juice
Basic Assessment Questions
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Answers
A. sand
mixture
B. water
compound
C. juice
mixture
Basic Assessment Questions
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Question 2
Classify each of the following as a chemical
or physical property.
A. density
B. reactivity
C. color
D. melting point
Basic Assessment Questions
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Answers
A. density
physical property
B. reactivity
chemical property
C. color
physical property
D. melting point
physical property