• A molecule is a group of 2 or more atoms linked together
chemically. Ex: H20, CH4, O2 ,H2 ,O3
• A compound is a molecule that contains 2 or more different
atoms. Ex: CH3COOH (vinegar)
Interesting molecules
• The caffeine molecule
• Lactic acid (in milk)
• Adrenalin!
Sugar
C12H22O11
Vitamin C
Fat molecule
Are you hungry?
Properties of molecules
• A molecule has different properties than the
atoms it’s composed of.
Example: Sodium, Na, is a reactive metal and
chlorine (Cl is a toxic gas!)
But the two atoms linked together give table
salt, that we eat. NaCl
Nomenclature and chemical formula
• Chemical formula: it is the name of a molecule
using symbols. Ex: NaCl, H2O, l, etc.
H2O
Subscript: indicates how
many atoms are
present. Affects the
atom on the left of it.
There are 2 atoms of
H and 1 atom of O
H2SO4 has 2 atoms of Hydrogen, 1 atom of sulfur, and 4 atoms
of oxygen.
Let’s practice!
Tell how many atoms of each kind there are in the following molecules:
a) MgCl2
b) Al2O3
c) H3PO4
d) NH3
e) HCN
f) C2H2
• Nomenclature: is the scientific name we use
to name a molecule.
• The common name of NaCl is table salt. The
scientific name is sodium chloride.
• The common name of CH3COOH is vinegar!
The scientific name is acetic acid.