In which you will learn about:
•Modeling atoms & molecules
•Chemical symbols & formulas
 We
live in a macroscopic world
• Large-scale, readily observed things
 Chemistry
explains what we observe in
the macroscopic world by describing the
interactions in the microscopic (particle)
world
 Scientists
use models to show objects that
are either really big or really small
• Models can also be used as simplifications of
complicated ideas
 It
is useful to use models of atoms &
molecules to “see” chemistry happening
 Draw
a model of two gaseous compounds
in a homogeneous mixture.
• A homogeneous mixture is uniform throughout,
so the two compounds should be intermingled
and evenly distributed.
• Compounds are composed of atoms of two or
more different elements linked together by
chemical bonds.
 An
international “chemical language” for
use in oral and written communication
was developed to represent atoms,
elements, and compounds
• The letters in this language’s alphabet are
chemical symbols which are understood by
scientists throughout the world
 Each
element is assigned a chemical
symbol
• Only the first letter of the symbol is capitalized
• All other letters are lowercase
 All
known elements are organized in the
periodic table of elements
 You are responsible for memorizing all of
the elements and symbols on the Elements
& Symbols sheet found in the Reference
Sheet section of the Honors Page
• Each set will be tested through quizzes
 Words
in the language of chemistry are
composed of letters (which represent
elements) from the periodic table
• Each word is a chemical formula, which
represents a different chemical substance
• A subscript (a number written below the normal
line of letters) indicates how many atoms of the
element just to the left of the subscript are in one
unit of the substance
H2O
2 atoms of hydrogen
1 atom of oxygen
 The
chemical formula for propane, a
compound commonly used as a fuel, is
C3H8. What elements are present in a
molecule of propane, and how many
atoms of each element are there?
 Answer: 3
hydrogen
atoms of carbon, 8 atoms of
 If
formulas are words in the language in
chemistry, then chemical equations can
be regarded as chemical sentences.
• Each chemical equation summarizes the details
of a particular chemical reaction
 Chemical
reactions entail the breaking
and forming of chemical bonds, causing
atoms to become rearranged into new
substances.
 The
new susbtances formed from a
chemical reaction have different
properties than those of the original
materials
• Starting material = reactant
• New substances formed = products
 An
arrow () represents the word
“yield”
• Reactants are on the left of the arrow
• Products are on the right of the arrow
 Two
hydrogen molecules react with one
oxygen molecule to yield two molecules
of water

2 H2 + O2  2 H2O
 The
large number out front of a formula is
called a coefficient
• Coefficients represent the number of molecules
of that type
 Perhaps
you noticed that in the chemical
equation on the previous slide, hydrogen
and oxygen had two atoms in their molecule
• These are examples of diatomic molecules
 There
are 7 diatomic elements that must be
memorized: hydrogen, nitrogen, oxygen,
fluorine, chlorine, bromine, iodine
 “GEN – U –INE DIATOMICS” serves as a
useful memory device for all common
diatomic elements.
• The names of all diatomic elements end in GEN or
INE and U should remember them!
 1)
Sketch a visual model on the
molecular level that represents each of
the following types of mixtures. Label
and explain the features of each sketch.
• A. a solution B. a suspension
 2) What
two pieces of information does a
chemical formula provide?

3) Name the elements and list the number of each
atom indicated in the following substances:
• A. phosphoric acid, H3PO4 (used in soft drinks)
• B. Sodium hydroxide, NaOH (found in some drain cleaners)
• C. sulfur dioxide, SO2 (an air pollutant)

4) Represent each chemical equation by drawing the
molecules and their component atoms. Use circles of
different sizes, colors, or shading for atoms of each
element. In H2O2, the oxygens are bonded in the
middle with hydrogens on the outside.
• A. H2 (g) + Cl2 (g)  2 HCl (g)
• B. 2 H2O2 (aq)  2 H2O (l) + O2 (g)
• C. Using complete sentences, write word equations for the
chemical equations given in A and B. Include the numbers of
molecules involved.