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 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds In nature, only the noble gas elements exist as uncombined atoms. They are monatomic; that is, they consist of single atoms. Helium, which is less dense than air, is often used to inflate balloons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds There are two ways elements can be like the nearest noble gas. Transfer electrons to form an ionic compound. Share electrons to form covalent compounds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electronegativity – ability of an atom to attract electrons when it is in a compound. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

Molecules and Molecular Compounds The electronegativity difference between two atoms tells you what kind of bond is likely to form. >2.0 tends to form an ionic bond <2 tends to form a covalent bond Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Covalent bond: a bond in which atoms are held together through the sharing of electrons Electron sharing usually occurs so that atoms attain the electron configuration of noble gases Molecule: a neutral group of atoms joined together by covalent bonds Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Work out how Flourine atoms would share electrons to form covalent bonds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Covalent bond: a bond in which atoms are held together through the sharing of electrons Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Molecule: a neutral group of atoms joined together by covalent bonds Examples: F2 H2O CH4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Diatomic molecule—a molecule that contains two atoms. Other elements found in nature in the form of diatomic molecules include hydrogen, nitrogen, oxygen, and the halogens. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Draw the electron dot structures for the following molecules. Chlorine Bromine Iodine Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Molecules can also be made of atoms of different elements. - Examples: H2O (water), CO2 (carbon dioxide), and N2O (nitrous oxide) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Molecular formula - chemical formula of a molecular compound. shows how many atoms of each element a substance contains H2O – 2 Hydrogen, 1 Oxygen C4H10 – 4 Carbon, 10 Hydrogen Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Identify the number and kinds of atoms present in a molecule of each compound. C6H8O6 – ascorbic acid (vitamin C) C12H22O11 – sucrose (table sugar) C7H5N3O6 – trinitrotoluene (TNT) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Properties of Molecular Compounds Lower melting and boiling points than ionic compounds Gases or liquids at room temperature Composed of atoms of two or more nonmetals Do not conduct electricity Usually do not dissolve in water Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule in Covalent Bonding Structural Formula: represents the covalent bonds as a line/dash between the two atoms that share electrons and shows the arrangement of covalently bonded atoms. H:H H-H Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule in Covalent Bonding Single Covalent Bond: atoms held together by sharing one pair of electrons Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule in Covalent Bonding Double Covalent Bond: a bond that involves two shared pairs of electrons Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule in Covalent Bonding Triple Covalent Bond: a bond formed by sharing three pairs of electrons Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bond Dissociation Energies Bond Dissociation Energy: energy required to break the bond between two covalently bonded atoms. Bond Bond Dissociation Energy (kJ/mol) Bond Length (pm) C C 347 154 C = C 657 133 908 121 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule of Covalent Bonding Draw Lewis Dot Structures for each molecular compound: SiO2 HCl H2O HCN Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule of Covalent Bonding Drawing Lewis Dot Structures: Determine # of valence electrons. Determine # of “octet” electrons. *Note*– Hydrogen gets 2 # bonds = (# octet e- - # valence e- ) Arrange atoms with # bonds from step 3. Hydrogen & halogens bond one time Group 6A elements bond 2 times Group 5A elements bond 3 times Carbon always bonds 4 times Add electron pairs until all atoms have the correct number of electrons around them Recheck your answer. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule of Covalent Bonding Exceptions to the Octet Rule Molecules whose total number of valence electrons is an odd number. 2. Boron wants 6 electrons for neutral molecules. 3. Phosphorus and sulfur expand the octet to 10 or 12 electrons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The Octet Rule of Covalent Bonding Resonance structures: structures that occur when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion. The ozone molecule has two possible electron dot structures. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Water, which is a molecular compound, and sodium chloride, which is an ionic compound, are compared here. Array of sodium ions and chloride ions Collection of water molecules Formula unit of sodium chloride Molecule of water Chemical formula H2O NaCl Chemical formula Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Classify compounds into groups according to their chemical bonding (ionic, covalent, or metallic). High or low melting point? Conduct electricity? Sodium chloride, NaCl Ammonia, NH3 Methane, CH4 Magnesium Oxide, MgO Aluminum, Al Barium Iodide, BaI2 Magnesium, Mg Cesium, Cs Oxygen, O2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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