Download Section 2.6

Section 2.6
Molecules and Molecular
Compounds
Remember…
• Atoms are the smallest representative
sample of an element Building Blocks
of Matter!
• BUT- only the noble gases are found as
isolated atoms
• The rest exist as molecules or ions
Molecules
• Assembly of two or more atoms tightly
bound together, behaving as a single
object
Chemical Formula
• Notation that uses chemical symbols and
subscript notation to convey relative
proportions of atoms of elements in a
molecule
Diatomic Molecule
• Molecule composed of two atoms
• Elements normally occurring as diatomic:
–Hydrogen (H2)
–Oxygen (O2)
–Nitrogen (N2)
–The halogens (F2, Cl2, Br 2, I2)
Molecular Compounds
• Compounds composed of molecules
• Contain more than one type of atom
• Examples: CH4, H2O, H2O2
Most molecular compounds contain only
nonmetals!!
Chemical Formulas
Molecular Formula
Empirical Formula
Molecular Formula
Empirical Formula
• Indicate the actual
• Only give the
numbers and types of
relative number of
atoms in a molecule.
atoms of each type in
a molecule.
• Subscript is always
the smallest possible
whole-number ratio
Examples
Hydrogen Peroxide
Molecular:
H 2 O2
Empirical:
HO
Ethylene
Molecular:
C 2H 4
Empirical:
CH2
Now You Try…
Glucose
Molecular:
Empirical:
Glucose
Molecular:
C6H12O6
Empirical:
Glucose
Molecular:
C6H12O6
Empirical:
CH2O
If we know the molecular
formula, we can determine the
empirical formula!
Does the converse hold true?
Structural Formula
• Shows which atoms are attached to each
other within a molecule
• Atoms are represented by their chemical
symbol
• Lines represent bonds
• Do not depict the geometry of the
molecule (the angles of the bonds)
Acetone
Perspective Drawings
• Structural formula that gives a sense of the
three-dimensional shape of a molecule
Methane
Ball-and-stick models
• Shows atoms as spheres and bonds as sticks
• Accurately represents angles of the bonds
• Also demonstrates relative size of atoms
Water
Space-filling models
• Depict a molecule scaled up to size
• Show relative size of atoms
• Difficult to see the angles of the bonds