Elements Combine to Form Compounds
Compounds
 Compound: a pure substance made up of more than one
kind of element in which the atoms of the elements are
joined together.
 Compounds form through chemical bonds: these are
links between two or more atoms that hold the atoms
together
 Two types of compounds
 Ionic Compounds: typically formed between metals and
non-metals. Ex. NaCl
 Molecular (covalent) compounds: formed between nonmetals only. Ex CO2
Compounds…
 Compounds are represented by a combination of element
symbols known as a chemical formula
 Chemical formulas indicate the proportion in which the
elements are present.
 Identify the elements and number of atoms for each
element in the following Chemical Formulas
CH4 Elements Present:
Carbon and Hydrogen
Proportion: (number of each element)
1 carbon atom and 4 hydrogen atoms
Complete the table below
Compound
CO2
CaCO3
C3H8
H2O
Elements Present
Proportion or
Number of each
element
Ionic Compounds
Name
Chemical Formula
Sodium Chloride (table salt)
NaCl
Calcium Carbonate (chalk)
CaCO3
Sodium Sulfate ???
Na2SO4
Sodium Hydroxide
NaOH
These are some common chemical ionic compounds
that you should know
Chemical Names of Compounds
 When given a chemical formula, you can write the
chemical name which indicates the elements present
in the compound
 IUPAC (International Union of Pure and Applied
Chemistry): a group that represent chemists around
the world and is responsible for the rules when naming
compounds.
Naming Ionic Compounds
 The first element is typically a metal and the name of
the metal is left unchanged
 The second element is a non-metal and the name always
end in “ide”
 Put the two names together
 What is the chemical name for the compound CaF?
 The first element is Ca: Calcium
 The second element is F: Fluorine but it needs to end in “ide”
so it becomes fluoride
 The name for CaF is calcium fluoride.
Task
 Complete the Practice Problems at the bottom of page
82.
Molecular Compounds
Compound Name
Chemical Formula
Table sugar (sucrose)
C12H22O11
Carbon Dioxide
CO2
Methane
CH4
Water
H2O
These are some common chemical molecular
compounds that you should know
Naming molecular Compounds
 Name the first Element
 Name the second element and use the suffix “ide”
 Add prefixes to the names to indicate the number of each atom in the
compound (see next slide for prefix names)
 Write the name of the compound
 Example: Name PF4
 First element is Phosphorous
 The second element is fluorine but the ending changes to ide so it is
fluoride
 There is only one P, so no prefix needed
 There are 4 F, so the prefix is tetra which gives tetrafluoride.
 The compound name is phosphorus tetrafluoride
Prefixes (table 3.4, page 83)
Number of atoms
Prefix
1
Mono (used only for the second atom)
2
di
3
tri
4
tetra
5
penta
6
hexa
7
hepta
8
octa
9
nona
10
deca
Task
 Practice problems on page 83
Physical and Chemical Changes
 Physical Change: the appearance of a substance may
be changed but the bonds holding the atoms together
have not been broken and new bonds have not been
made. NO NEW SUBSTANCE IS PRODUCED.
 Examples of Physical Changes:
 Change of state
 Cutting
 Dissolving
 Chemical Change: produces new substances with
new properties. New bonds are formed while other
bonds are broken
 Examples of Chemical Changes
 Corrosion (metals combining with oxygen)
 Combustion (burning)
 Fruit Ripening
Useful Websites
 http://videos.howstuffworks.com/hsw/8685-states-of-
matter-chemical-changes-video.htm
 http://www.quia.com/quiz/303980.html
Evidence that a chemical change
may have occurred
 Heat is produced or absorbed
 A new color appears
 A precipitate is formed
 A gas is produced
 Difficult to reverse
Note: these observations do not prove conclusively that
a chemical change has occurred but it supports the
possibility that it is a chemical change.
Brainstorm
 Are there examples of changes that are not easily
identified as chemical or physical?
 It is not always a clear cut situation!
Core Lab
Observing Changes in Matter
Chemical Change
 During a chemical change, elements are conserved but
compounds are not
 Corrosion or the rusting of iron: In a piece of steel, iron
atoms are bonded together.
 Overtime, oxygen will combine with the iron to form
something new, rust.
 The number of iron atoms has not changed but they are
now combined with oxygen to form a new compound
Task
 How many different structures has you make from 5 red
leggos, 6 blue and 4 white. Will everyone's structure be the
same? No, but the number of red, blue and white leggos in
the structures will be the same.
 If the colored leggos represent 3 different elements,
then the same number and types of elements can
produce different compounds (or structures in this
case)