Download SCH4C Junior Chemistry Review - Molecular Compounds

2/13/2011
Molecular Elements
• A MOLECULE is a combination of two or more
atoms held together by covalent bonds.
• A COVALENT BOND is a connection, between two
non-metals, in which the two atoms SHARE a pair
of electrons.
• Several non-metals exist as molecules
• DIATOMIC MOLECULES are made up of 2 atoms
Review Topic Five:
Molecular Compounds
Properties, Naming and Writing Chemical Formulas
• Bohr diagram can illustrate the SHARING
of electrons in a covalent bond between
two chlorine atoms.
Remember!
Covalent bonds
involving SHARING
of electrons
Elemental chlorine is a diatomic
molecule (Cl2). Chlorine
dissolves in water and is
used to disinfect water in drinking
supplies and swimming pools.
Properties of Molecular Compounds
• Molecular compounds are often
soft
• If they dissolve in water, they form
solutions that do NOT conduct
electricity
• Tend to have relatively LOW
melting points
– Table sugar (sucrose)
Naming Binary
Molecular Compounds
• Binary compounds consist
of exactly TWO elements.
• Naming binary molecular
compounds that do NOT
contain hydrogen atoms
use GREEK prefixes to
indicate how many atoms
are present
Writing Binary Molecular Compounds
Naming Binary Molecular Compounds
Steps
1. Name the first element.
Example
N2O
nitrogen
2. Name the second element
oxide
using the suffix “-ide”.
3. Add prefixes to indicate
the number of each atom.
dinitrogen
monoxide
Example
PBr3
phosphorus
bromide
phosphorus
tribromide
Steps
Example
disulphur
decafluoride
Example
carbon
tetrachloride
• The prefix “mono-” is NOT used when the first
element is only one atom.
1. Identify the first element,
and give its symbol.
S
C
• When the prefix “mono-” is required for
before “oxide”, the last “o” in the prefix is
dropped, it is “monoxide” NOT “monooxide”.
2. Identify the second
element, and give its
symbol.
3. Add subscripts to indicate
the numbers of atoms.
F
Cl
“di”  2
“deca”  10
“tetra”  4
S2F10
CCl4
Using “mono-” Properly
4. Write the formula
1