Atoms, Molecules, Compounds and Mixtures
Atoms
Atoms: The smallest unit into which an
element can be divided and still retain
the properties of that element.
An atom refers to a single unit.
Examples:
Atoms
In a sphere and stick model, an atom is
represented by a circle, a bond is
represented by a straight line.
Atom
Examples:
Bond
Molecule
Molecule: Formed when two or more atoms
combine through a chemical bond.
Molecules can be formed by:
1.Two or more different atoms (Compound)
2.One type of atom (Element)
Examples:
Compound
Element
Chemical Bonds
Chemical bonds are formed between atoms- the
result of electron sharing in an attempt to
gain stability.
When one pair of electrons is shared, it is
called a single bond.
Example:
Quick Check
Look at the diagram below. How many unbonded
atoms are there?
Quick Check
How many atoms are there total (bonded and
unbonded)?
Quick Check
How many molecules are in this picture?
Quick Check
How many compounds are in this picture?
Quick Check
How many element molecules are in this
picture?
Mixtures
Mixtures are substances that are
physically mixed, but not chemically
bonded.
Examples:
Mixtures will
have no single
chemical formula.
Chemical Formulas
Chemical formulas are an abbreviated
way to write out the chemical
composition of a substance.
For example, the substance dichlorofluoromethane, can
be written by its chemical formula:
CF2Cl2 (This is commonly
called Freon)
Chemical Formulas
Chemical formulas show exactly what
elements can be found in a molecule.
CF2Cl2
Carbon
Fluorine
Chlorine
Subscripts
Subscripts are used to note how many of each
atom are present in the molecule. No
subscript behind an element indicates there
is 1 atom.
CF2Cl2
Carbon (1)
Fluorine
(2)
Chlorine (2)
Coefficients
Coefficients are large numbers in front
of the chemical formula. They are used
to indicate how many molecules are
present. No number in front indicates 1
molecule.
CF2Cl2
No number = 1
molecule of
Freon (CF2Cl2)
Quick Check
How many molecules of baking soda are
shown by the chemical formula here:
2NaHCO3
This is the coefficient.
It tells you how many
molecules there are.
Quick Check
How many elements can be found in
baking soda ?
2NaHCO3
Na – Sodium
H – Hydrogen
C – Carbon
O - Oxygen
Quick Check
How many atoms can be found in 1
molecule of baking soda?
NaHCO3
1 Na
1 H 1 C
3 O
TOTAL = 6
Coefficients and Subscripts
When your formula contains BOTH a
coefficient AND subscripts, an
additional step must be taken to
calculate the total number of atoms:
H2O =
Coefficients and Subscripts
When your formula contains BOTH a coefficient
AND subscripts, an additional step must be
taken to calculate the total number of atoms:
3H2O =
Coefficients and Subscripts
3H2O =
The coefficient must be multiplied
through the entire formula to calculate
the total number of atoms.
Coefficients and Subscripts
3H2O =
3 x (2) = 6 H
3 x (1) = 3 O
TOTAL ATOMS = 9
Quick Check
How many total atoms are found in
this formula for bleach?
5NaClO
5 x (1) = 5 Na
5 x (1) = 5 Cl
5 x (1) = 5 O
TOTAL =
15 Atoms
Quick Check
How many atoms of Oxygen are found
in this formula for quartz?
3SiO2
3 x (2) = 6 atoms of
Oxygen
Quick Check
How many atoms of Silicon are found
in this formula for quartz?
3SiO2
3 x (1) = 3 atoms of
Silicon