Molecular CompoundsSection 8.1
Objectives When you complete this
presentation, you will be able to … distinguish between the melting
points and boiling points of molecular compounds and ionic compounds.
describe the information provided by a molecular formula.
Introduction Molecular compounds are like the combinations we
can make from a Tinker-Toy set: There are a certain number of hub pieces that are
different colors. There are a certain number of connecting pieces.
Likewise, we have limits on the number and kinds of … atoms that we can use to make molecular compounds bonds that we can use to join the atoms together
Molecules and Compounds
Matter in nature takes on many forms. Noble gases exist as individual atoms.
They are monoatomic. They have very low melting points and boiling points.
We just learned about ionic compounds and metallic compounds. They exist as ions in a crystalline structure. They have high melting points and boiling points.
We will now learn about a different kind of matter that is much more varied in its properties.
This kind of matter is called a molecular compound.
Molecules and Compounds
Molecular compounds are bound together by sharing electrons between atoms. The bond formed is called a covalent bond.
The neutral compounds formed with covalent bonds are called molecules. Molecules formed from two atoms are called diatomic
molecules. HCl H2
O2
Molecules and Compounds
All of the molecules of a given molecular compound are all the same. All of the molecules in water are H2O.
All of the molecules in carbon dioxide are CO2.
Ionic compounds are not the same as molecular compounds. For example, there is no such thing as a CaCl2 molecule.
In general, molecular compounds tend to have relatively lower melting points and boiling points that ionic compounds. This mean that covalent bonds are weaker than ionic bonds.
Molecular Formulas A molecular formula is the chemical formula of a
molecular compound.
The molecular formula tells us exactly how many of each type of atom a molecule contains. Each molecule of water, H2O, contains two hydrogen
atoms and one oxygen atom. Each molecule of glucose, C6H12O6, contains six carbon
atoms, twelve hydrogen atoms, and 6 oxygen atoms.
A molecular formula has the total number of atoms in a molecule – it is not a lowest whole number ratio.
Molecular Formulas A molecular formula does not tell us anything about
the actual three-dimensional structure of the compound.
Molecular Formulas A molecular formula does not tell us anything about
the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH3,
does not show the distribution of atoms in space.
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH3,
does not show the distribution of atoms in space.
Molecular Formulas
NH3
Molecular formula
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH3,
does not show the distribution of atoms in space.
Molecular Formulas
H−N−H
H
. .−
NH3
Molecular formula Structural
formula
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH3,
does not show the distribution of atoms in space.
Molecular Formulas
H−N−H
H
. .−
NH3
Molecular formula Structural
formula Perspective drawing
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH3,
does not show the distribution of atoms in space.
Molecular Formulas
H−N−H
H
. .−
NH3
Molecular formula Structural
formula Perspective drawing
Space-filling molecular model
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH3,
does not show the distribution of atoms in space.
Molecular Formulas
H−N−H
H
. .−
NH3
Molecular formula Structural
formula Perspective drawing
Space-filling molecular model
Ball-and-stick molecular model
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O)
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O)
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O)
H H−
−O
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O) Carbon dioxide (CO2)
H H−
−O
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O) Carbon dioxide (CO2)
H H−
−O
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O) Carbon dioxide (CO2)
H H−
−O O=C=O
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O) Carbon dioxide (CO2) Ethanol (C2H6O)
H H−
−O O=C=O
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O) Carbon dioxide (CO2) Ethanol (C2H6O)
H H−
−O O=C=O
A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. We can look at other molecules to see the three
dimensional arrangement of atoms vs. the molecular formulas.
Molecular Formulas
Water (H2O) Carbon dioxide (CO2) Ethanol (C2H6O)
H H−
−O O=C=O CH3 OH−
−CH2
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