Download A chemical property produces a change in the composition of matter

Chapter Three : Properties & Changes
Chapter Three Section One:
Properties of Matter
Matter is the “stuff” that everything is
composed of. It can also be defined as
anything that has mass and takes up
space (volume)
Matter can be divided into pure
substances and mixtures based on their
compositions.
Pure Substances – any matter that always
has exactly the same composition –
Examples : Water, Table Sugar and Sodium
Hydrogen Carbonate
Any sample of a pure substance has the
same properties because it has a fixed,
uniform composition.
Pure Substances can be classified into two
categories:
elements or compounds
Classification of Matter
© 2009, Prentice-Hall, Inc.
Classification of Matter
© 2009, Prentice-Hall, Inc.
Classification of Matter
© 2009, Prentice-Hall, Inc.
Classification of Matter
© 2009, Prentice-Hall, Inc.
Classification of Matter
© 2009, Prentice-Hall, Inc.
The classification of matter is
summarized below.
Prentice Hall © 2007
Chapter One
Elements – Simplest Forms of Matter
• Elements cannot be broken down into
simpler substances
• An element has a fixed composition
because it is made up of only one type of
atom
• The atom is the smallest particle of an
element. The atoms of each element differ
from the atoms of every other element.
Characteristics of Elements
Most elements exist as solids at room temperature (200 C
or 680 F)
Some elements are gases at room temperature
Only two elements (bromine-Br and mercury-Hg) are
liquids at 00 C
Element symbols consist of either a single letter or two
letters. Single element symbols are always capitalized;
element symbols consisting of two letters have the first
letter capitalized while the second letter is not capitalized
(lower case)
Compounds
• Compounds are made from two or more
simpler substances (elements) and can
be broken down into those simpler
substances
• The properties of a compound differ from
those substances from which it is made
• The two or more elements composing a
compound are always joined in a fixed
proportion (H2O)
Capsaicin biosynthetic pathway.
Prasad B C N et al. PNAS 2006;103:13315-13320
©2006 by National Academy of Sciences
Mixtures
• The properties of a mixture can vary
because the composition of a mixture is
not fixed
• Mixtures are classified by how well the
parts of a mixture mix with each other
• Mixtures can be heterogeneous or
homogeneous
Characteristics of Heterogeneous and
Homogeneous Mixtures
• Heterogeneous mixtures are not well mixed.
The parts of the mixtures are noticeably
different from one another.
Examples: Grains of Sand; Mud and Water; Oil
and Water
• Homogeneous mixtures are so well mixed the
substances in the mixture cannot be
distinguished from one another.
Examples: Sweetened Tea; Swimming Pool
Water; Stainless Steel Dinnerware
Special Types of Mixtures
• Certain mixtures are classified according to the size of
their largest particles: Solutions; Suspensions; Colloids
• Solutions – the largest particles are so small that they
dissolve in the mixture so they are no longer visible –
sugar and water
• Solutions do not separate into distinct layers over time;
solutions cannot be filtered and they remain clear.
• Suspensions are mixtures which mix in such a way that
the particles remain suspended in the liquid for an
extended period of time but will eventually separate
out. Suspensions can be filtered into their component
parts.
• Colloids contain some particles that are
intermediate in size between the small
particles of a solution and the larger
particles of suspension. Colloids do not
separate into layers and cannot be
filtered into their different particles. –
• Examples: Milk; Fog
2.2 Physical Properties of Matter
• A physical property is any characteristic
of a material that can be observed or
measured without changing the
composition of the substances in the
material.
Examples of physical properties are:
viscosity, conductivity, malleability,
hardness, melting point, boiling point,
density
• Viscosity – the resistance of a liquid to flow; the
greater the viscosity of a liquid the slower the
liquid flows – Examples: high viscosity -honey
and corn syrup; low viscosity – vinegar and
milk
• Conductivity – the materials ability to allow heat
to flow – Examples: all metals are good
conductors of heat; wood is a poor conductor
of heat
• Malleability – the ability of a solid to be
hammered without shattering ; Examples – most
metals can be hammered into different shapes
solids which break or shatter when hammered
are said to be brittle Examples: ice and glass
• Hardness – compares the hardness of two or
more materials to each other – which material
will scratch another material or be scratched
by that material – Example: stainless steel knife
scratching a copper sheet
• Melting and Boiling Points – the temperature at
which a substance changes from a solid to a
liquid (melting point); the temperature at which
a substance boils (boiling point)
• Density – the ratio of the mass of a substance to
its volume (Density(g/cm3 ) =
mass(g)/volume(cm3) Density is used to test
the purity of a substance
Figure 12
• Physical properties are used to identify a
material, to choose a material for a specific
purpose or to separate the substances in a
mixture.
• Examples:
Calculating densities of metals to determine
what they are made of using the conductivity
rating of materials to determine if they could
be used to make pots for cooking
•
Filtration and distillation are two common
methods used to separate the parts of a
mixture
2.3 Chemical Properties of Matter
• A chemical property produces a change in the
composition of matter; these properties can be
observed only when the substances in a
sample of matter are changing into different
substances – Examples:
Flammability – the burning of a material in the
presence of oxygen
Reactivity - describes how readily a
substance combines chemically with other
substances
Recognizing Chemical Changes
• A chemical change occurs when a substance
reacts and forms one or more new substances
Three common ways to recognize a chemical
change:
• Color change – copper metal changing color;
iron metal rusting
• Production of a gas – mixing baking soda
with vinegar produces carbon dioxide gas
• Formation of a precipitate – a solid forms and
separates when two substances are mixed
What Makes a Change Physical or
Chemical?
• A chemical change produces a change
in the composition of matter
• A physical change occurs when some of
the characteristics of matter change but
the composition of matter remains the
same
Separation
of Mixtures
© 2009, Prentice-Hall, Inc.
Distillation
Distillation uses
differences in the
boiling points of
substances to
separate a
homogeneous
mixture into its
components.
© 2009, Prentice-Hall, Inc.
Filtration
In filtration solid
substances are
separated from
liquids and solutions.
© 2009, Prentice-Hall, Inc.
Chromatography
This technique separates substances on
the basis of differences in solubility in a
solvent.
© 2009, Prentice-Hall, Inc.