Embed Size (px)
Citation preview
12/2/13
1
8.1 Molecular Compounds >
1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Chapter 8 Covalent Bonding 8.1 Molecular Compounds 8.2 The Nature of Covalent Bonding 8.3 Bonding Theories 8.4 Polar Bonds and Molecules
8.1 Molecular Compounds >
2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
What information does a molecular formula provide?
Molecules and Molecular Compounds
8.1 Molecular Compounds >
3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
In nature, only the noble gas elements, such as helium and neon, exist as uncombined atoms.
Molecules and Molecular Compounds
• Monatomic molecules
8.1 Molecular Compounds >
4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
But not all elements are monatomic.
Molecules and Molecular Compounds
• O2 represents two oxygen atoms that are bonded together.
• What are the 7 diatomic molecules?
12/2/13
2
8.1 Molecular Compounds >
5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
Ionic compounds are generally crystalline solids with high melting points.
Molecular compounds, however, have very different properties.
• Water (H2O) is a liquid at room temperature.
• Carbon dioxide (CO2) and nitrous oxide (N2O) are both gases at room temperature.
8.1 Molecular Compounds >
6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• do not involve the transfer of electrons.
Molecules and Molecular Compounds
The attractions that hold together the atoms in O2, H2O, CO2, and N2O are not ionic bonds.
8.1 Molecular Compounds >
7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• Molecular compounds combine by sharing electrons.
Molecules and Molecular Compounds
Sharing Electrons
– covalent bond
8.1 Molecular Compounds >
8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• Oxygen gas consists of oxygen molecules; each oxygen molecule consists of two covalently bonded oxygen atoms.
Sharing Electrons
Molecules and Molecular Compounds
A molecule is a neutral group of atoms joined together by covalent bonds.
12/2/13
3
8.1 Molecular Compounds >
9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• A molecular formula shows how many atoms of each element a substance contains.
Molecules and Molecular Compounds
Representing Molecules
8.1 Molecular Compounds >
10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
Representing Molecules
The molecular formula of water is H2O.
• The subscript after an element’s symbol indicates the number of atoms of each element in the molecule.
• the subscript 1 is omitted.
8.1 Molecular Compounds >
11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• The molecular formula for butane is C4H10.
• One molecule of butane contains four carbon atoms and ten hydrogen atoms.
Molecules and Molecular Compounds
Representing Molecules Butane is also a molecular compound.
8.1 Molecular Compounds >
12 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• The subscripts are not necessarily the lowest whole-number ratios.
Molecules and Molecular Compounds
Representing Molecules A molecular formula reflects the actual number of atoms in each molecule.
12/2/13
4
8.1 Molecular Compounds >
13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
Representing Molecules
A molecular formula does not tell you about a molecule’s structure.
8.1 Molecular Compounds >
14 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
8.1 Molecular Compounds >
15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
Representing Molecules
The arrangement of atoms within a molecule is called its molecular structure.
8.1 Molecular Compounds >
16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
Representing Molecules The arrangement of atoms within a molecule is called its molecular structure.
12/2/13
5
8.1 Molecular Compounds >
17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Molecules and Molecular Compounds
Representing Molecules
The arrangement of atoms within a molecule is called its molecular structure.
8.1 Molecular Compounds >
18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Acetylsalicylic acid, also known as aspirin, has a molecular formula of C9H8O4. What elements make up acetylsalicylic acid? How many atoms of each element are found in one molecule of acetylsalicylic acid?
8.1 Molecular Compounds >
19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Comparing Molecular and Ionic Compounds
What representative units define molecular compounds and ionic compounds?
Comparing Molecular and Ionic Compounds
8.1 Molecular Compounds >
20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
The representative unit of a molecular
compound is a molecule. For an ionic compound, the smallest
representative unit is a formula unit.
Comparing Molecular and Ionic Compounds
12/2/13
6
8.1 Molecular Compounds >
21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• Recall that a formula unit is the lowest whole-number ratio of ions in an ionic compound.
– A molecule is made up of two or more atoms that act as a unit.
– No such units exist in an ionic compound
– continuous array of ions
– There is no such thing as a molecule of sodium chloride or magnesium chloride.
Comparing Molecular and Ionic Compounds
8.1 Molecular Compounds >
22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• So, Many molecular compounds are gases or liquids at room temperature.
Comparing Molecular and Ionic Compounds
Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.
8.1 Molecular Compounds >
23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
• Ionic compounds
• formed from a metal combined with a nonmetal
• Higher melting points and boiling points
• Solids at room temperature
Comparing Molecular and Ionic Compounds
8.1 Molecular Compounds >
24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Comparing Molecular and Ionic Compounds
Collection of water molecules
1 Molecule of Water made up of 3
atoms
Chemical formula H2O
Array of sodium ions and chloride ions in a
crystal
Formula unit of sodium chloride
made up of 2 ions
Chemical formula NaCl
12/2/13
7
8.1 Molecular Compounds >
25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
How is the formula unit of an ionic compound different from a molecule?
