Chapter
9 Classification of Matter
9.1
Composition of Matter
Chemists
study and classify matter – the endless array of materials that we come into
contact with each day. Matter can be defined as anything that has mass and
takes up space. It can be classified into three groups: elements, compounds
and mixtures.
v The units that make up all matter are called atoms.
v If all the atoms in a sample
of matter have the same identity that kind of matter is called an element.
Oxygen, hydrogen, copper, zinc and lead are all elements.
v An element is a substance
that cannot be broken down into other substances.
v Altogether there are 111
recognized elements.
Compounds
v
Materials
called compounds are made from atoms of two or more elements that are
chemically combined. The ratio of the different atoms in a compound is always
the same.
v Hydrogen and oxygen can
combine to form the compound water (H20): 2 atoms of Hydrogen and 1
atom of oxygen.
v A compound that you eat
almost daily consisting of a black element and two invisible gases is called
sugar. It consists of carbon, oxygen and hydrogen.
v Compounds usually have a
different appearance from the elements that make them up. Water is made up of
two elements that are flamable gases
v
A
substance is either an element or a compound. Elements and compounds
cannot be reduced to more basic components by physical processes. (heating,
cooling, cutting, stretching etc.)
v
Oxygen,
carbon, water, sugar, baking soda and salt are all examples of materials
classified as a substance.
Mixtures
v
A
mixture is a material made up of two or more substances that can be separated
by physical means. Mixtures retain their individual properties. Saltwater is a
mixture of water (H20) and salt (NaCl). Both water and salt are
compounds.
v
A
mixture in which different materials can be easily distinguished is called a heterogeneous
mixture. Pizza, concrete (sand, gravel), dry soup mixes are examples.
Heterogeneous mixtures can be seen with the naked eye or with a microscope.
v
Mixtures
that are uniform throughout are homogeneous.
Solutions
v
Mixtures
that are clear (you can’t see any particles) and are uniformly spread out are
called a homogeneous mixture. Saltwater is a homogeneous mixture, so is
a carbonated beverage (CO2 in H2O). Solutions are always
clear. They can be colorless or colored.
v
A
solution is another name for a homogeneous mixture. In a solution particles are
so small they cannot be seen. They will never settle out.
Colloids
and Suspensions
v
A
colloid is a heterogeneous mixture that, like a solution, will never settle
out.
v
Colloids
scatter light. This effect is called the Tyndall effect.
v
A suspension is a heterogeneous mixture containing a liquid in which
visible parts will settle out. Muddy water is an example.
v
A
solute is any substance that dissolves into another substance. Salt is
the solute in saltwater.
v
A
solvent is the substance that some other substance dissolves into. Water is a
solvent. It is the most common solvent in the universe.
Kinds of
Solutions
|
Example
|
|
Solid in Solid |
Steel
(Carbon and Iron) |
|
Liquid in Solid |
Rubber
cement (benzene in rubber) |
|
Gas in Solid |
Alloy
of Palladium and hydrogen |
|
Solid in Liquid |
Saltwater
(salt in water) |
|
Liquid in Liquid |
Vinegar
(acetic acid in water) |
|
Gas in Liquid |
Carbonated
Beverage (carbon dioxide CO2 in water) |
|
Gas in Gas |
Air |
|
Solid in Gas |
Perfume
(perfume particles in air) |
|
Liquid in Gas |
Humid
Air (water in air) |