A pure substance that
cannot be broken down
into simpler substances by
physical or chemical means.
Elements are considered pure…
…because all of the particles are identical.
of an element is
called an atom
of that element.
How are elements found?
• Some elements are found in nature in
their pure, natural form. (Gold &
• Other elements are chemically and/or
physically combined with other
elements in nature and need to be
separated from the other elements to
get a pure sample.
Scientists made a list of all the known elements
and organized it on a chart (table) called the
Periodic Table of the Elements.
Periodic Table of Elements
If it is an element, it is on the table
Periodic Table of Elements
If it is not an element, it is not on the table (chart).
Element Names and Symbols
• Some element names match their symbol
– Hydrogen (H)
– Helium (He)
– Oxygen (O)
– Carbon (C)
• Other Elements do not seem to match their
symbol at all.
– Gold (Au)
– Silver (Ag)
– Mercury (Hg)
• This is because their symbol matches their
name from a different language.
– Gold is Aurum in Latin so the Au matches it’s Latin
– Silver is Argentium in Latin so the Ag matches it’s
– Mercury is Hydragyrm in Latin so the Hg matches it’s
Scientists from all over the world use the same
symbols and the same Periodic Table even if they
have different common names for elements.
The symbol for gold is always (Au) even if its
common name is:
– Oro in Italian - Kin in Japanese
– Or in French - Jin l in Chinese
– Guld in Swedish - Geum in Korean
– Zloto in Polish - Thongkam in Thai
– Auksas in Lithuanian - Emas in Indonesian
– Dhahab in Arabic - Kulta in Finnish
– Zahaz in Hebrew - Chrysos in Greek
• The smallest possible particle of an
element is called an atom of that element.
•A pure substance made of two or
more elements that are chemically
•This new substance usually has very
different properties than the original
elements combined to form it.
•Each particle of a compound is called
a molecule of that compound.
Examples of Compounds
• Water (H20) is made of two parts Hydrogen
and one part Oxygen.
• Hydrogen is a clear gas that is highly volatile
and explodes if placed near a flame.
• Oxygen is a clear gas that reacts with many
substances and is required for most things to
• When chemically combined they form water
which is a clear liquid that will not burn and
does not react with many substances.
• Hydrogen (white) Again, it is a
• Oxygen (purple) pure substance
and all the
identical to each
other. But, each
particle is made
of more than one
Table Salt (Sodium Chloride) NaCl
• Table salt is made of one part sodium and
one part chlorine.
• Sodium (Na) is a silver solid that burns
violently when it touches water.
• Chlorine (Cl) is a yellowish gas that is so
poisonous that it is illegal to use in war.
• When Chemically combined they form the
compound sodium chloride (NaCl) which is
table salt, a white solid that is edible.
• Sodium (purple)
• Chlorine (green)
• When two or more compounds or elements are
physically (but not chemically) combined.
• The original substances keep their properties and
no new substances are created
• They can be separated by physical means.
• They are considered “not pure substances”.
Examples of Mixtures
• Sugar water - When sugar is mixed with
water, the sugar and the water keep their
properties because they still exist.
• The mixture can be separated by physical
Identify each as an element,
compound or mixture.
• Each element has its own symbol
• These symbols always begin with a
• If they have a second or third letter
they are always lower case
C for Carbon
O for Oxygen
Co for Cobalt
• The symbol for a compound is
composed of more than one chemical
• The chemical formula for carbon
dioxide is CO2.
• This means that a molecule of carbon
dioxide is composed of one atom of
carbon and two atoms of oxygen
• A chemical equation is a set of
symbols that describes what is
occurring in a chemical reaction.
• In the equation Na + Cl à NaCl
Na (sodium) and Cl (chlorine) are the
reactants and NaCl (salt) is the
Reactants and Products
• The reactants are the substances
that you have originally, before
the chemical change and the
products are what is created
during the chemical change.
Organization of the Periodic Table
• The periodic table is organized into
families based on their similar properties
• Elements in the same vertical column will
react similar when combined with a
• Example: Sodium reacts with Chlorine to
produce salt (NaCl). Lithium and Bromine
will react similarly with Chlorine.