Comparing covalent compounds
Intermolecular bonds
• To determine relative melting points for ionic
compounds, we looked at the strength of
intramolecular bonds (bonds between atoms).
Intermolecular bonds
• To determine relative melting points for ionic
compounds, we looked at the strength of
intramolecular bonds (bonds between atoms).
• To determine relative melting points for
covalent compounds, we looked at the
strength of intermolecular bonds (bonds
between adjacent molecules).
Intermolecular bonds
• To determine relative melting points for ionic
compounds, we looked at the strength of
intramolecular bonds (bonds between atoms).
• To determine relative melting points for
covalent compounds, we looked at the
strength of intermolecular bonds (bonds
between adjacent molecules).
• Single, double, and triple bonds tell us nothing
about relative melting point.
Melting point for covalent compounds
• First, we must determine the polarity of the
molecule. Polar molecules have higher
melting points than nonpolar molecules.
Melting point for covalent compounds
• First, we must determine the polarity of the
molecule. Polar molecules have higher
melting points than nonpolar molecules.
• If both compounds are polar, the one with the
greater electronegativity difference will have a
higher melting point.
Melting point for covalent compounds
• First, we must determine the polarity of the
molecule. Polar molecules have higher
melting points than nonpolar molecules.
• If both compounds are polar, the one with the
greater electronegativity difference will have a
higher melting point.
• If both compounds are nonpolar, the one with
a greater number of overall electrons will have
the higher melting point.
Melting point visual aid
Which substance has a higher melting
point, CO or CO2?
Which substance has a higher melting
point, CO or CO2?
• We need to determine the polarity of each
substance. The difference in electronegativity
will be the same for each compound, 0.89.
Which substance has a higher melting
point, CO or CO2?
• We need to determine the polarity of each
substance. The difference in electronegativity
will be the same for each compound, 0.89.
• Lewis structure for CO will not be symmetrical
and is polar.
Which substance has a higher melting
point, CO or CO2?
• We need to determine the polarity of each
substance. The difference in electronegativity
will be the same for each compound, 0.89.
• Lewis structure for CO will not be symmetrical
and is polar.
• Lewis structure for CO2
O = C = O  nonpolar
Which substance has a higher melting
point, CO or CO2?
• We need to determine the polarity of each
substance. The difference in electronegativity
will be the same for each compound, 0.89.
• Lewis structure for CO will not be symmetrical
and is polar.
• Lewis structure for CO2
O = C = O  nonpolar
• CO has the higher melting point
Which substance is more likely to be a gas
at room temperature, NH3 or PBr3?
Which substance is more likely to be a gas
at room temperature, NH3 or PBr3?
• NH3 is polar according to the Lewis structure.
Which substance is more likely to be a gas
at room temperature, NH3 or PBr3?
• NH3 is polar according to the Lewis structure.
• PBr3 is also polar according to its Lewis
structure.
Which substance is more likely to be a gas
at room temperature, NH3 or PBr3?
• NH3 is polar according to the Lewis structure.
• PBr3 is also polar according to its Lewis
structure.
• The substance with the smaller difference in
electronegativity will will have weaker
intermolecular bonds and is more likely to be
a gas at room temperature.
Which substance is more likely to be a gas
at room temperature, NH3 or PBr3?
• NH3 is polar according to the Lewis structure.
• PBr3 is also polar according to its Lewis
structure.
• The substance with the smaller difference in
electronegativity will will have weaker
intermolecular bonds and is more likely to be
a gas at room temperature.
• PBr3
Which substance has a higher boiling point,
N2 or O2?
Which substance has a higher boiling point,
N2 or O2?
• Both substances have an electronegativity
difference of zero and are nonpolar.
Which substance has a higher boiling point,
N2 or O2?
• Both substances have an electronegativity
difference of zero and are nonpolar.
• The substance with more electrons will have
the higher boiling point.
Which substance has a higher boiling point,
N2 or O2?
• Both substances have an electronegativity
difference of zero and are nonpolar.
• The substance with more electrons will have
the higher boiling point.
• N2 has 14 electrons, O2 has 16 electrons,
oxygen has the higher boiling point.
Naming binary covalent compounds
• A binary covalent compound consists of
exactly two nonmetals.
Naming binary covalent compounds
• A binary covalent compound consists of
exactly two nonmetals.
• The name of the first nonmetal is the name of
the element with a latin prefix to represent
the subscript (unless it’s 1).
Naming binary covalent compounds
• A binary covalent compound consists of
exactly two nonmetals.
• The name of the first nonmetal is the name of
the element with a latin prefix to represent
the subscript (unless it’s 1).
• The name of the second nonmetal must end
in -ide with a latin prefix to represent the
subscript (even if it’s 1).
Latin prefixes
1. mono-
Latin prefixes
1. mono2. di-
Latin prefixes
1. mono2. di3. tri-
Latin prefixes
1.
2.
3.
4.
monoditritetra-
Latin prefixes
1.
2.
3.
4.
5.
monoditritetrapenta-
Latin prefixes
1.
2.
3.
4.
5.
6.
monoditritetrapentahexa-
Latin prefixes
1.
2.
3.
4.
5.
6.
7.
monoditritetrapentahexahepta-
Latin prefixes
1.
2.
3.
4.
5.
6.
7.
8.
monoditritetrapentahexaheptaocta-
Examples
• CCl4 =
Examples
• CCl4 = carbon tetrachloride
• P2O5 =
Examples
• CCl4 = carbon tetrachloride
• P2O5 = diphosphorus pentoxide
• CO =
Examples
• CCl4 = carbon tetrachloride
• P2O5 = diphosphorus pentoxide
• CO = carbon monoxide