Describing Molecular Compounds
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Transcript Describing Molecular Compounds
Molecular Compounds:
Formulas & Naming
Ch 6.3b - Covalent Bonds
What type of bond?
Covalent
– Electrons are shared between atoms
– Forms between non-metals
– Covalent Bonds Molecular
Compounds
Which
elements are non-metals?
Describing Molecular
Compounds
What information do the name and formula
of a molecular compound provide?
Ionic Bonds (Ionic Compounds) – The name distinguishes the compound from
other ionic compounds containing the same
elements.
– The formula of an ionic compound describes
the ratio of the ions in the compound.
Describing Molecular
Compounds
Covalent Bonds (Molecular
Compounds)
– The name and formula of a
molecular compound describe the
type and number of atoms in a
molecule of the compound.
Naming Molecular Compounds
Naming Order:
Step 1: Element that is farthest to the left side of the
periodic table is typically named 1st. (left to right)
– The most metallic element appears first in the name.
These elements are farther to the left in the periodic
table.
If both elements are in the same group, the more metallic
element is closer to the bottom of the group.
– Formulas are written same way
Example:
–
Sulfur is named before chlorine SCl2
Naming Molecular Compounds
Exception: Oxygen & Halogens
–
–
Oxygen comes 2nd when combined with lowerelectronegativity halogens (Group 17)
Example: ClO2 (electronegativity: Cl = 3.0; O = 3.5)
Step 2: Second element name is changed to end in
“ide” (like the anion in an ionic compound)
Examples:
–
–
Chlorine becomes chloride
Oxygen becomes oxide
Naming Molecular Compounds
There may be more than one molecular compound
that can exist with the same two elements.
–
Greek prefixes are used to name molecular compounds.
Step 3: Add prefixes to elements names to specify
the number of atoms of each element in the
compound.
mono - one hexa - six
di - two
hepta - seven
tri - three
octa - eight
tetra - four nona - nine
penta - five deca - ten
Naming Molecular Compounds
Prefixes:
• mono - one
• di - two
• tri - three
• tetra - four
• penta - five
Example:
Both Compounds contain
Nitrogen and Oxygen
N2O
Dinitrogen monoxide
N4O5
Tetranitrogen pentoxide
Naming Molecular Compounds
Exception
to Step 3– No prefix is used
if there is only one atom of the 1st
element in the compound.
Carbon monoxide
CO2 Carbon dioxide
SO10 Sulfur decaoxide
CO
Naming Molecular Compounds
More Examples:
– Dinitrogen
pentachloride
N2Cl5
– Dinitrogen
pentoxide
N2O5
– Pentaphosphorous
hexachloride
P5Cl6
– Sulfur decaoxide
SO10
Writing Molecular Formulas
Step 1: Write the symbols for the elements in
the order the elements appear in the name.
Step 2: Write the numerical value of the prefixes
as subscripts for the corresponding element in
the formulas.
– The prefixes indicate the number of atoms of each
element in the molecule.
– If there is no prefix for an element in the name, there
is only one atom of that element in the molecule.
Writing Molecular Formulas
Examples:
– Diphosphorus Pentoxide P2O5
– Silcon Dioxide SiO2
– Carbon Tetrachloride CCl4
– Trineptunium Octoxide Np3O8
You Try
Give
the formula for:
– Oxygen Difluoride
– Phosphorus Tribromide
– Trisilicon Tetranitride
Give the Name
– NO2
– N2O3
– SO3
for:
You Try - Answers
Give
the formula for:
– Oxygen Difluoride OF2
– Phosphorus Tribromide PBr3
– Trisilicon Tetranitride Si3N4
Give
the Name for:
– NO2 Nitrogen Dioxide
– N2O3 Dinitrogen Trioxide
– SO3 Sulfur Trioxide