MATTER
Since the study of chemistry is the study of matter and the changes it goes
through we need to know what is considered matter and how it is classified.
Below you will find some information about matter.
matter - anything that takes up space (has volume) and has mass
mass - a measure of the amount of matter in an object
Mass is used as the measurement of the amount of matter in an object
because it is a constant. The volume of an object can change with
temperature and the weight of an object can change with location. Matter
normally exists in 3 states (phases).
Solids
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matter with with definite shape and volume
solids usually have a high density compared to their liquid or gas form
solids only expand slightly when heated
solids are almost incompressible
Liquids
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matter that flows and takes the shape of its container
liquids have a fixed volume
liquids are usually less dense than their solid form (water is the
exception)
liquids only expand slightly when heated
liquids are almost incompressible
Gases
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matter that takes the shape and volume of its container
gases are less dense than their solid or liquid form
gases expand without limit when heated
gases are easily compressed
The terms gases and vapor are often used interchangeably, but in science
their is a difference between the two. The term gas is used for a substance
that normally exists as a gas at room temperature, like oxygen. The term
vapor is used for a substance that normally exists as a liquid or solid at room
temperature, like water. Water can exist in the gaseous state in the air at
room temperature, but normally it is found in the liquid state.
It is possible for matter to exist in a fourth state under extreme conditions.
This fourth state of matter is called plasma. Plasma is a gas that has been
heated to a very high temperature. When a gas is heated to high
temperatures the molecules separate into atoms and electrons are stripped
from the atoms. In order to form plasma a gas must be heated to
temperatures of 50,000 °C or higher.
Matter can be classified into two main categories, Pure Substances and
Mixtures.
Pure Substances - matter that has a uniform and definite composition. All
pure substances have the same properties and characteristics. For example,
pure water (H2O) has the same properties and characteristics whether it is
found in Minnesota or in Africa. Pure substances can be either elements or
compounds.
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Element - An element is the simplest form of matter that cannot be
broken down into other substances. Elements can be found on the
Periodic Table and there are 109 of them, of which 91 are found in
nature. Examples of elements are: sulfur, iron, oxygen, hydrogen
Compound - A compound is a substance that is made up of two or
more elements chemically combined. Elements in a compound can
only be separated by a chemical reaction. Examples of compounds
are: NaCl, H2O, CO2
Mixtures - a physical blend of 2 or more substances where each substance
retains its properties. An example would be a mixture of sugar and salt.
Each substance retains its properties and they can be separated by physical
means (without a chemical reaction). Mixtures are either homogeneous or
heterogeneous.
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Homogeneous Mixture - a mixture with uniform composition
throughout (evenly distributed). Homogeneous mixtures are also
called solutions in chemistry. Examples would be: saltwater,
homogenized milk, or brass (a mixture of copper and zinc).
Heterogeneous Mixture - a mixture that is not uniform in
composition. The substances are not evenly distributed in this type of
mixture and they may even contain more than one phase. Examples
would be: vegetable soup, soil, or pizza.
We can describe and identify matter by physical and chemical properties.
We can also observe matter undergoing change during physical and
chemical changes.
Physical Property - a property that can be observed without changing the
substance's composition. Examples sould be: density, melting points,
boiling points, color, odor, or hardness. All of these properties can be
measured or observed without changing the compostion of the substance.
Chemical Property - a property that describes the ability of a substance to
undergo a chemical reaction and form a new substance. For example, a
chemical property of sodium is that it will react in water to form hydrogen
gas and sodium hydroxide.
Extensive Property – a property that depends on the amount of matter in
the sample. Examples would be mass, weight, and volume.
Intensive Property – a property that does not depend on the amount of
matter in the sample. Examples would be density, melting and boiling
points.
Physical Change - altering a substance without changing its composition.
Examples would be: cutting, tearing, melting, boiling, or grinding. You can
perform any of these actions on a substance without changing what it is
made of.
Chemical Change - a change that results in the formation of 1 or more new
substances. Chemical changes cannot take place without a chemical reaction
occuring. Examples would be: rusting of iron, or burning of paper. In each
example one or more new substances are forming.
Chemical Reactions
When a chemical reaction takes place the starting substances in the reaction
are called reactants and the new substances that form are called products.
Chemical equations are an abbreviated way to show what is reacting and
what is forming in a chemical reaction by using the symbols of the elements
involved. An example of a chemical reaction is: solid sodium metal reacts
with chlorine gas to yield solid sodium chloride with the release of heat.
The chemical equation for this reaction is shown below.
Na(s) + Cl2(g) ------------------- 2NaCl + heat
Reactants
Products
The reaction shown above is exothermic because heat is released in the
reaction. In an exothermic reaction heat is shown on the side with the
products. A reaction where heat is taken in is said to be endothermic and
the heat is shown on the side with the reactants. In any reaction, whether it
is physical or chemical, the total energy on the reactants side must equal the
total energy on the products side. This is true because of the Law of
Conservation of Energy which states: energy cannot be created or
destroyed in any physical or chemical reaction; energy is just converted from
one form to another. Energy that is stored (potential energy) in the
substances reacting gets converted into other forms of energy, such as heat.
In an exothermic reaction the reactants have more stored (potential) energy
than the products since the stored energy of the products plus the heat
released must equal the total energy of the reactants. In an endothermic
reaction the stored energy of the products is greater than the stored energy of
the reactants because the reactants are taking in heat to increase their total
stored energy.
Element Types & the Periodic Table
The periodic table is a tool used in chemistry that has elements arranged in
rows (periods) and columns (groups) based on the elements properties. The
left side of the periodic table is composed of metals and the upper right side
of the periodic table is composed of nonmetals. The diagonal stairway in
outlined on our periodic table on the wall is the boundary between these two
types of elements. Elements that border on the stairway are called
metalloids and can have properties of both metals or nonmetals, depending
on conditions. The following properties are associated with the different
types of elements.
Metals
 Good conductors of electricity and heat
 Malleable (can be pounded into sheets)
 Ductile (can be stretched into wires)
 Lustrous (shiny)
Nonmetals
 Poor conductors of electricity and heat
 Brittle
 Non-lustrous (with a very few exceptions)
The nonmetals in the far right column on the periodic table are called Noble
gases and are very unreactive. They are found in very few compounds while
most of the elements on the rest of the periodic table react with each other to
form many different compounds.