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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.
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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
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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.
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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 H2H2 O2O2
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Molecules and Compounds All of the molecules of a given molecular compound are all the same. All of the molecules in water are H 2 O. All of the molecules in carbon dioxide are CO 2. Ionic compounds are not the same as molecular compounds. For example, there is no such thing as a CaCl 2 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.
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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, H 2 O, contains two hydrogen atoms and one oxygen atom. Each molecule of glucose, C 6 H 12 O 6, 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.
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Molecular Formulas A molecular formula does not tell us anything about the actual three-dimensional structure of the compound.
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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, NH 3, does not show the distribution of atoms in space.
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A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH 3, does not show the distribution of atoms in space. Molecular Formulas NH 3 Molecular formula
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A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH 3, does not show the distribution of atoms in space. Molecular Formulas H−N−H H. − NH 3 Molecular formula Structural formula
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A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH 3, does not show the distribution of atoms in space. Molecular Formulas H−N−H H. − NH 3 Molecular formula Structural formula Perspective drawing
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A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH 3, does not show the distribution of atoms in space. Molecular Formulas H−N−H H. − NH 3 Molecular formula Structural formula Perspective drawing Space-filling molecular model
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A molecular formula does not tell us anything about the actual three-dimensional structure of the compound. For example: the molecular formula for ammonia, NH 3, does not show the distribution of atoms in space. Molecular Formulas H−N−H H. − NH 3 Molecular formula Structural formula Perspective drawing Space-filling molecular model Ball-and-stick molecular model
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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
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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 (H 2 O)
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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 (H 2 O)
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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 (H 2 O) HH − − O
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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 (H 2 O)Carbon dioxide (CO 2 ) HH − − O
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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 (H 2 O)Carbon dioxide (CO 2 ) HH − − O
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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 (H 2 O)Carbon dioxide (CO 2 ) HH − − O O=C=O
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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 (H 2 O)Carbon dioxide (CO 2 )Ethanol (C 2 H 6 O) HH − − O O=C=O
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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 (H 2 O)Carbon dioxide (CO 2 )Ethanol (C 2 H 6 O) HH − − O O=C=O
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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 (H 2 O)Carbon dioxide (CO 2 )Ethanol (C 2 H 6 O) HH − − O O=C=O CH 3 OH − − CH 2
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