Transcript Chemistry 101 2007

Chemistry 101 2007
Instructor:
Dr. Robert D. Hancock, Ph.D., D.Sc.
Chemistry is the central science
MEDICINE
BIOLOGY
MATERIALS
SCIENCE
ENVIRONMENTAL
SCIENCE
AGRICULTURE
GEOLOGY
CHEMISTRY
PHYSICS
FUELS,
ENERGY
Classifications of matter.
Sections 1.1 through 1.3.
1.1 The Atomic and molecular
Perspectives of Chemistry.
Chemistry is the study of the properties
and behavior of matter.
A property is a characteristic that
allows us to recognize a particular type
of matter.
All the matter in the world is comprised
of about 116 elements.
The basic building blocks of matter are
atoms. Here are some atoms:
Hydrogen
Chlorine
carbon
sodium
nitrogen
oxygen
potassium
Atoms can combine to form molecules, in
which two or more atoms are joined together:
Dioxygen
Molecule
(O2)
Carbon
dioxide
carbon
oxygen
atom
Hydrogen
peroxide
ethanol
Red = oxygen
hydrogen
atom
cyan = carbon
white = hydrogen
1.2. Classifications of matter.
Matter can be classified according to
its physical state: solid, liquid or gas.
It can also be classified according to its
composition: element, compound, or
mixture.
States of matter.
Gas: Has no fixed volume or shape.
Expands to fill its container.
Gas molecules
all moving about
at high speed to
fill container
Liquid. Has a fixed volume but no fixed
shape – takes on the shape of that part of
the container that it fills.
water molecules
in liquid water are
loosely associated
Solid. Has a definite shape and a
definite volume, e.g. diamond:
carbon atoms
In a solid like diamond each
carbon atom is joined to four other
carbons in a definite arrangement
diamond lattice
viewed edge-on
Pure Substances:
Most forms of matter are not chemically
pure, e.g. air is a mixture. A pure
substance has distinct properties and
composition that do not vary from
sample to sample. Water and table salt
are pure substances. All pure
substances are either elements or
compounds.
ELEMENTS cannot be decomposed into
simpler substances.
These are like the pieces used to make Lego models.
Elements contain only one kind of atom. Some
elements are:
Oxygen
carbon
phosphorus
Compounds are substances
composed of two or more elements.
Sodium
chloride
(table
salt)
butanol
(brake
fluid)
octanol
(gasoline)
glucose
(sugar)
Mixtures are combinations of two or
more substances in which each
substance retains its chemical identity.
These can be heterogeneous or
homogeneous. Heterogeneous
mixtures are things like wood or rocks
or sand. One can see that these differ
from point to point in the mixture.
Heterogeneous mixture
is seen under microscope
to be composed of several
different types of materials
Homogeneous mixtures are also
called solutions.
Air is a homogeneous
mixture of oxygen and
nitrogen
A solution of NaCl
in water is a
homogeneous mixture
Some other mixtures:
Brass an alloy
Homogeneous
coffee – a solution
homogeneous
Some other mixtures:
Granite
(heterogeneous)
vinaigrette
(heterogeneous)
Compounds:
Most elements can interact with other
elements to form compounds (which
cannot?). e.g. H2 and O2 combine with
each other to form water, H2O. The
properties of water are very different
from those of H2 and O2.
O2 (gas) + H2 (gas) = H2O (liquid)
Law of constant composition or
constant proportions:
The elemental composition of a compound is
always the same. E.g. water is always 11% H
and 89% O. ‘Natural” water?
1.3. Properties of matter.
These can be physical properties,
which can be measured without
changing the identity and composition
of the substance. Examples are color,
odor, density, melting point, boiling
point, and hardness.
Chemical properties
Chemical properties describe how a
substance can change, or react, to form
other substances. E.g. flammability.
Octane
(gasoline)
oxygen
(gas)
(8 molecules)
carbon dioxide + water
(gas)
Intensive properties.
Intensive properties. Do not depend on
the amount of the substance, e.g.
melting point, temperature, density.
Big piece of ice melts
at 100 oC
small piece of ice melts
at 100 oC
Extensive properties.
Extensive properties. Depend on
amount, e.g. weight, volume.
Big piece of ice has volume
of 105 cc and weighs 100 g
small piece is 5.25 cc
and weighs 5 g
PHYSICAL AND CHEMICAL
CHANGES.
Physical change: Substance changes its appearance,
but not its composition. e.g. ice to water.
Chemical change. A substance is transformed into a
chemically different substance.
Burning of wood
(chemical change)
melting of ice
(physical change)
Physical or Chemical Property?
Zinc (Zn):
Silver-grey metal
physical property
Melting point 420 ºC
physical property
Reacts with O2 to form ZnO
chemical property
Density = 7.13 g/cm3
physical property
Dissolves in H2SO4
to give H2 gas
chemical property
Physical or Chemical Process?
Sugar dissolving in water.
Physical process
The picture on the left represents
a) compounds in the gas phase
b) Homogeneous mixture of
elements in the gas phase
c) Mixture of molecules in the
gas phase
d) a heterogeneous mixture of
elements
e) a mixture of molecules in the
liquid phase
HW: 1, 2
Chapter 1: Introduction
Classification of Matter
(2) Molecules, Elements, Compounds, Pure Substances, and Mixtures
Phase state?
Molecules
or atoms?
gas
solid and gas
solid
gas
Molecules
Atoms
Atoms
Molecules
and atoms
Compound?
yes
no
no
no
Mixture?
no
yes
yes
yes
-
heterogeneous
homogeneous
homogeneous
- what kind?
Separation of mixtures:
Mixtures can be separated by for example:
Filtration
distillation
chromatography