Classification of Matter
1. Introduction
2. Classifying Matter
2.1. Examples of Homogeneous Mixtures, also known as Solutions
2.2. Examples of Heterogeneous Mixtures
2.3. Example of a Colloidal Mixture Whose Components Tend Not to Settle Out
3. Separation of Mixtures
4. States of Matter
4.1. Solids
4.2. Liquids
4.3. Gases
5. Other States of Matter
6. Outside links
7. References
8. Problems
9. Contributors
Introduction
A substance is a sample
of matter whose physical and chemical properties are the same
throughout the sample because the matter has a constant composition. It
is common to see substances changing from one state of matter to
another. To differentiate the states of matter at least at a particle level, we look at the behavior of the particles within the substance. When substances
change state, it is because the spacing between the particles of the
substances is changing due to a gain or loss of energy. For
example, we all have probably observed that water can exist in three
forms with different characteristic ways of behaving: the solid
state (ice), liquid state (water), and gaseous state (water vapor and
steam). Due to water's prevalence, we use it to exemplify and describe
the three different states of matter. As ice is heated and the particles
of matter that make up water gain energy, eventually the ice melts in
to water that eventually boils and turns into steam.
Before we examine the states of matter,
we will consider some ways samples of matter have been classified by
those who have studied how matter behaves.
Classifying Matter
Evidence suggests that substances
are made up of smaller particles that are ordinarily moving around. Some
of those particles of matter can be split into smaller units using
fairly strong heat or electricity into smaller rather uniform bits of
matter called atoms. Atoms are the building blocks of elements.
Elements are all those substances that have not ever been decomposed or
separated into any other substances through chemical reactions, by the
application of heat, or by attempting to force an direct electric
current through the sample.
Atoms in turn have been found to be made up of yet smaller units of matter called electrons, protons, and neutrons.
Elements can be arranged into what is called the periodic table of elements
based on observed similarities in chemical and physical properties
among the different elements. When atoms of two or more elements come
together and bond, a compound is formed. The compound formed can later
be broken down into the pure substances that originally reacted to form
it.
Compounds such as water are composed of
smaller units of bonded atoms called molecules. Molecules of a compound
are composed of the same proportion of elements as the compound as a
whole since they are the smallest units of that compound. For example,
every portion of a sample of water is composed of water molecules. Each
water molecule contains two hydrogen atoms and one oxygen atom, and so
water as a whole has, in a combined state, twice as many hydrogen atoms
as oxygen atoms..
Water can still consist of the same
molecules, but its physical properties may change. For instance, water
at a temperature below 0 degrees Celsius (32 degrees Fahrenheit) is ice,
whereas water above the temperature of 100. degrees Celsius (212
degrees Fahrenheit) is a gas, water vapor. When matter changes from one
state to another, temperature and pressure may be involved in the
process and the density and other physical properties change. The
temperature and pressure exerted on a sample of matter determines the
resulting form of that the matter takes, whether solid, liquid, or gas.
Since the properties of compounds and elements are uniform, they are classified as substances.
When two or more substances are mixed together, the result is called a
mixture. Mixtures can be classified into two main categories:
homogeneous and heterogeneous. A homogeneous mixture is
one in which the composition of its constituents are uniformly mixed
throughout. A homogeneous mixture in which on substance, the solute,
dissolves completely in another substance, the solvent, may also be
called a solution. Usually the solvent is a liquid,
however the solute can be either a liquid, solid, or a gas. In a
homogeneous solution, the particles of solute are spread evenly among
the solvent particles and the extremely small particles of solute cannot
be separated from the solvent by filtration through filter
paper because the spaces between paper fibers are much greater than the
size of the solute and solvent particles. Other examples of homogeneous
mixtures include sugar water, which is the mixture of sucrose and water,
and gasoline, which is a mixture of dozens of compounds.
A heterogeneous mixture
is a nonuniform mixture in which the components separate and the
composition varies. Unlike the homogeneous mixture, heterogeneous
mixtures can be separated through physical processes. An example of a
physical process used is filtration, which can easilty separate the sand
from the water in a sand-water mixture by using a filter paper. Some
more examples of heterogeneous mixtures include salad dressing, rocks,
and oil and water mixtures. Heterogeneous mixtures involving at least
one fluid are also called suspension mixtures and
separate if they are left standing long enough. Consider the idea of
mixing oil and water together. Regardless of the amount of time spent
shaking the two together, eventually oil and water mixtures will
separate with the oil rising to the top of the mixture due to its lower
density.
Mixtures that fall between a solution and a heterogeneous mixture are called colloidal suspensions
(or just colloids). A mixture is considered colloidal if it typically
does not spontaneously separate or settle out as time passes and cannot
be completely separated by filtering through a typical filter paper. It
turns out that a mixture is colloidal in its behavior if one or more
of its dimensions of length, width, or thickness is in the range of
1-1000 nm. A colloidal mixture can also be recognized by shining a beam
of light through the mixture. If the mixture is colloidal, the beam of
light will be partially scattered by the suspended nanometer sized
particles and can be observed by the viewer. This is known as the Tyndall effect. In
the case of the Tyndall effect, some of the light is scattered since
the wavelengths of light in the visible range, about 400nm to 700 nm,
are encountering suspended colloidal sized particles of about the same
size. In contrast, if the beam of light were passed through a solution,
the observer standing at right angles to the direction of the beam
would see no light being reflected from either the solute or solvent
formula units that make up the solution because the particles of solute
and solvent are so much smaller than the wavelength of the visible light
being directed through the solution.
- Solutions: molecules ~0.1-2 nm in size
- Colloids: molecules ~ 2-1000 nm in size
- Suspensions: molecules greater than ~ 1000 nm in size
Examples of Homogeneous Mixtures, also known as Solutions
Filtered seawater is solution of the compounds of water, salt (sodium chloride), and other compounds.
Examples of Heterogeneous Mixtures
separation of sand and water separation of salad dressing various mixtures within a rock
Example of a Colloidal Mixture Whose Components Tend Not to Settle Out
Figure 4: milk is a colloid of liquid butterfat globules suspended in water
Separation of Mixtures
Most substances are naturally found as
mixtures, therefore it is up to the chemist to separate them into their
natural components. One way to remove a substance is through the
physical property of magnetism. For example, separating a mixture of
iron and sulfur could be achieved because pieces of iron would be
attracted to a magnet placed into the mixture, removing the iron from
the remaining sulfur. Filtration is another way to
separate mixtures. Through this process, a solid is separated from a
liquid by passing through a fine pored barrier such as filter paper.
Sand and water can be separated through this process, in which the sand
would be trapped behind the filter paper and the water would strain
through. Another example of filtration would be separating coffee
grounds from the liquid coffee through filter paper. Distillation
is another technique to separate mixtures. By boiling a solution of a
non-volatile solid disolved in a liquid in a flask, vapor from the lower
boiling point solvent can be driven off from the solution by heat,
be condensed back into the liquid phase as it comes in contact with
cooler surfaces, and be collected in another container. Thus a solution
such as this may be separated into its original components, with the
solvent collected in a separate flask and the solute left behind in the
original distillation flask. An example of a solution being separated
through distillation would be the distillation of a solution of
copper(II) sulfate in water, in which the water would be boiled away and
collected and the copper(II) sulfate would remain behind in the
disllation flask.
States of Matter
Everything that is familiar to us in our daily lives - from the land we walk on, to the water we drink and the air we breathe - is based upon the states of matter called gases, liquids, and solids.Solids
When the temperature of a liquid is lowered to the freezing point of the substance (for water the freezing point is 0oC), the
movement of the particles slows with the spacing between the particles
changing until the attractions between the particles lock the particles
into a solid form. At the freezing point, the particles are closely
packed together and tend to block the motions of each other. The
attractions between the particles hold the particles tightly together so
that the entire ensemble of particles takes on a fixed shape. The
volume of the solid is constant and the shape of a solid is constant
unless deformed by a sufficiently strong external force. (Solids are
thus unlike liquids whose particles are slightly less attracted to one
another because the particles of a liquid are a bit further apart than
those in the corresponding solid form of the same substance.) In a
solid the particles remain in a relatively fixed positions but continue
to vibrate. The vibrating particles in a solid do not completely stop
moving and can slowly move into any voids that exist within the solid.
Figure 2: The diagram on the left represents a solid whose constituent particles are arranged in an orderly array, a crystal lattice. The
image on the right is a ice cube. It has changed from liquid into a
solid as a result of absorbing energy from its warmer environment.
Liquids
When the temperature of a sample
increases above the melting point of a solid, that sample can be found
in the liquid state of matter. The particles in the liquid state are
much closer together than those in the gaseous state, and still have a
quite an attraction for each other as is apparent when droplets of
liquid form. In this state, the weak attractive forces within the liquid
are unable to hold the particles into a mass with a definite shape.
Thus a liquid's shape takes on the shape of any particular container
that holds it. A liquid has a definite volume but not a definite shape.
Compared to to the gaseous state there is less freedom of particle
movement in the liquid state since the moving particles frequently are
colliding with one another, and slip and slide over one another as a
result of the attractive forces that still exist between the particles,
and hold the particles of the liquid loosely together. At a given
temperature the volume of the liquid is constant and its volume
typically only varies slightly with changes in temperature.
Figure 3: The diagram on the left represents a container patially filled with a liquid. The image on the right is of water being poured out of a glass. This shows that liquid water has no particular shape of its own.
Gases
In the gas phase, matter does not have a
fixed volume or shape. This occurs because the molecules are widely
separated with the spaces between the particles typically around ten
times further apart in all three spatial directions, making the gas
around 1000 times less dense than the corresponding liquid phase at the
same temperature. (A phase is a uniform portion of mater.) As the
temperature of a gas is increased, the particles to separate further
from each other and move at faster speeds. The particles in a gas move
in a rather random and independent fashion, bouncing off each other and
the walls of the container. Being so far apart from one another, the
particles of a real gas only weakly attract each other such that the gas
has no ability to have a shape of its own. The extremely weak forces
acting between the particles in a gas and the greater amount of space
for the particles to move in results in almost independent motion of the
moving, colliding particles. The particles freely range within any
container in which they are put, filling its entire volume with the net
result that the sides of the container determine the shape and volume of
gas. If the container has an opening, the particles heading in the
direction of the opening will escape with the result that the gas as a
whole slowly flows out of the container.
Figure 4: The image on
the left represents an enclosed container filled with gas. The images
are meant to suggest that the gas particles in the container are moving
freely and randomly in myriad directions.The image on the right shows
condensing water forming from the water vapor that escaped from the
container.
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