Elements vs. Compounds
Elements
Elements are found on the periodic table. There are ~120 elements. The
individual units of elements are atoms. For example, we can refer to the element
“gold” or we can refer to individual gold atoms.
Elements are represented with either a capital letter or a capital letter and a
lowercase letter. This is the element’s chemical symbol. You can count the
number of capital letters to determine how many elements are present.
Examples:
C – 1 element – carbon
O – 1 element – oxygen
Co – 1 element – cobalt
CO – 2 elements – carbon and oxygen
Compounds
Everything around us (solids, liquids and gases) is made from combinations
of one or more of the atoms of elements on the periodic table. When atoms of
elements combine chemically (or bond) they form molecules or compounds.
Signs that a molecule or compound are present rather than just an atom are:
 Subscripts – numbers written below and after the element symbol.
Subscripts indicate how many atoms of that particular element are present.
No subscript written after the chemical symbol indicates only 1 atom of that
element is present.
EXAMPLE: H2 – molecule of hydrogen gas made from two
hydrogen atoms
 More than one capital letter
EXAMPLE: CO – molecule of carbon monoxide made from one
carbon atom and one oxygen atom
 There may also be a combination of the above
EXAMPLE: H2O – molecule of water made from two atoms of
hydrogen and one atom of oxygen
Organic Compounds
 Organic compounds have at least 1 carbon atom and 2 hydrogen atoms
(CH2). They may have more of each, but this is the minimum.
 They often also have other atoms such as Sulfur (S), oxygen (O),
phosphorus (P), and nitrogen (N).
Atoms and Compounds
Written Atom or
formula molecule?
Al
Coefficient:
# of separate
atoms or
molecules
3Zn
Model
1
aluminum
atom
Al
1 atom
3 atoms
Atoms
involved
Zn
Zn
Zn
H2
1 molecule
H
2H2
2
molecules
H
H
2
hydrogen
atoms
H
Subscript: #
of atoms in
one molecule
O
2SiO2
2
molecules
O
3 zinc
atoms
H
H
4
hydrogen
atoms
O
2 silicon
atoms
Si
Si
O
4 oxygen
atoms
None of these are organic compounds since they do
not contain at least 2 carbon atoms and 1 hydrogen
atom together.
Name ________________________
Science Teacher ______________________
Complete the table for each of the formulas listed:
Formula
Atom or
molecule?
Model
Organic?
Reason
CO2
3C
N2
2CH3
Name ________________________
Science Teacher ______________________
Complete the table for each of the formulas listed:
Formula
CO2
3C
N2
2CH3
Atom or
molecule?
Model
Organic?
Reason