1. Henry R. Kang (1/2010)
General Chemistry
Lecture 2
Matter
2. Henry R. Kang (1/2010)
Matter and Substance
• Matter is anything that has mass and volume.
This definition practically includes everything in
this universe, except energy.
Einstein brought mass and energy together
E = mc2
E is the energy, m is the mass, and c is the velocity of
light.
• Matters are classified into two groups:
Substance
Examples: water, ammonia, gold, and oxygen
Mixture
Examples: coffee, sea water, air, etc.
3. Matter
Mixtures
(A combination of two or more
substances. No constant composition)
Heterogeneous
mixtures
(Components are
not uniformly
distributed.
Boundaries exist
between
components)
Homogeneous
mixtures
(Same
composition at
any part of the
mixture. No
boundary
between
components)
Substances
(Definite composition
and distinct properties)
Compounds
(A substance composes of
atoms of two or more
elements chemically united
in fixed proportions)
Elements
(Cannot be divided into
simpler substances by
chemical means. There
are 117 elements)
Separation by
physical methods
Separation by
chemical methods
Ionic compound Molecule AtomAllotrope
Subatomic particles
(proton, neutron, electron, etc.)
Cation Anion
Isotopes
Henry R. Kang (1/2010)
4. Henry R. Kang (1/2010)
Substance
• A substance is a form of matter that has a
definite composition and distinct properties.
A substance always has the same characteristic
properties, regardless where and when it is
obtained and how it is prepared.
Example:
Sodium chloride is a solid at room temperature and the
melting point is always 801°C.
• A substance cannot be separated into other
kinds of matter by any physical process.
5. Henry R. Kang (1/2010)
Element
• An element is a substance that cannot be
separated into simpler substances by chemical
means (or chemical reaction).
• 117 elements have been identified.
They are organized in a table called “periodic table”.
See next slide
82 elements occur naturally on Earth
carbon (6), aluminum (13), gold (79), lead (82), etc.
35 elements have been created by scientists
Americium (95), curium (96), berkelium (97), californium
(98), einsteinium (99), fermium (100), etc.
8. Henry R. Kang (1/2010)
Compound
• A compound is a substance that is composed of two or
more atoms of different elements chemically united in
fixed proportions.
For examples, carbon monoxide (CO: C/O=1/1), nitrogen
dioxide (NO2: N/O=1/2), water (H2O: H/O=2/1), ammonia
(NH3: N/H=1/3), glucose (C6H12O6: C/H/O=1/2/1).
The fixed proportions are usually in small integer ratios (Law of
definite proportions).
Note that H2, O2, and O3 are not compounds (only one
element); they are elements and molecules.
• Compounds can be separated into their pure
components (elements) by chemical means.
9. Henry R. Kang (1/2010)
Mixture
• A mixture is a combination of two or more
substances in which the substances retain
their distinct identities.
The components of a mixture coexist.
The ratios of substances in the mixture can be
varied.
A mixture can be separated by physical
means into substances.
10. Henry R. Kang (1/2010)
Type of Mixtures
• Homogenous mixture (or solution)
The composition and appearance of the mixture is
the same everywhere, having the same properties
throughout a given sample.
Examples: soft drink, milk, solder, gasoline, etc.
• Heterogeneous mixture
The composition is not uniform throughout,
containing physically distinct parts, separated by
boundaries (phases), each with different properties.
Examples: cement, iron filings in sand, a piece of
wood, etc.
11. Henry R. Kang (1/2010)
Separation of Mixture
• Physical means (filtration, evaporation,
precipitation, etc.) can be used to separate a
mixture into its pure components (or
substances).
• Examples
Distillation to separate mixtures of two liquids such
as alcohol from water.
Evaporation to separate solid from liquid such as
salt from sea water.
Magnet to separate iron filings from sand.
12. Henry R. Kang (1/2010)
Physical State
and
Chemical Constitution
of Substances
13. Henry R. Kang (1/2010)
Three Physical States of Matter
• Solid
Solid has fixed shape and volume, independent with respect to the
container.
Practically incompressible
Molecules or atoms are held close together in an orderly fashion with a rigid
structure, having little freedom of movement.
• Liquid
A given amount of liquid has a fixed volume but no fixed shape, which is
defined by the container.
Relatively incompressible fluid
Molecules or atoms are relatively close together but are not held so rigidly in
position and can move past one another.
• Gas
A given quantity of gas has no fixed size and shape, they are defined by
the container.
Easily compressible fluid
Particles are separated by long distances (much longer than the size of the
substance) with large void space between them.
Gas particles move freely within the container.
14. Henry R. Kang (1/2010)
Phase Change
• Phase change is a change of the state of a single matter,
accompanying by the transform of physical properties
and appearance.
Three states of a matter can be inter-transformed without
changing the composition of the substance, but there is a
change of appearance with a distinct boundary between
states.
• Example:
Water at normal conditions (e.g. room temperature) is in a
liquid state.
Put a glass of water in a refrigerator, the liquid water freezes
to solid ice.
A pot of liquid water when heats above 100°C becomes
steam.
15. Henry R. Kang (1/2010)
Changes of Matter
• Physical change
Physical change is the changes of physical properties and
appearance of a matter, but not its chemical composition.
Examples:
Ice melting.
Sugar dissolving in water.
• Chemical change
Chemical change, or chemical reaction, is the change of
chemical composition of a matter into a different kind of
matter or several different kinds of matter.
Examples:
Burn gasoline to form carbon dioxide and water.
Sodium metal in water produces hydrogen gas and sodium hydroxide
16. Henry R. Kang (1/2010)
Properties of Matter
• Physical Property
It can be measured and observed without changing
the chemical composition and identity of a matter.
Examples: Color, density, melting point, etc.
• Chemical Property
Chemical property of a matter can only be measured
where the chemical composition of the matter is
changed.
Example: To know the energy release by propane, we
need to burn it.
