Chemistry Matter and Change Chapter 8 Covalent Bonding
Chapter 8 Main Idea Covalent bonds form when atoms share electrons.
Chemistry Matter and Change Chapter 8 The Covalent Bond
Atoms gain stability when they share electrons and form covalent bonds. 8.1 Main Idea
8.1 Objectives • Apply the octet rule to atoms that form covalent bonds. • Describe the formation of single, double, and triple covalent bonds. • Contrast sigma and pi bonds. • List the diatomic elements • Relate the strength of a covalent bond to its bond length and bond dissociation energy.
Review Vocabulary & Concepts • Chemical bond • Valence electrons • Electronegativity • Lewis structure
New Vocabulary & Concepts • Covalent bond • Molecule • Sigma (σ)bond • Pi (π)bond • Endothermic reaction • Exothermic reaction • Single bond • Double bond • Triple bond
Why do Atoms Bond? • Sharing electrons takes less energy than being “alone” • Octet is usually the most stable electron configuration
What is a covalent bond? • Shared pairs of electrons • http://www.glencoe.com/sites/common_assets/science/cmc/cim/animations/ch8_3_1.swf
Single Covalent Bonds • Two atoms share one pair of electrons • Sigma bond (σ) • Either : or _ for a Lewis Structure ·+ · · · H H H HorH-H
Multiple Covalent Bonds • Two atoms share more than one pair of electrons • One pair is a sigma bond (σ)the others are pi (π)bonds • Double bond shares 2 pair of electrons • Triple bond shares 3 pair of electrons
Double Covalent Bonds A π bond A σ bond
Comparing Bonds Sigma (σ) Bonds Pi (π) Bonds • Single • Centered • s orbital electrons • One pair of electrons is shared • Paired • Parallel • p orbital electrons • Multiple pairs of electrons are shared
Diatomic Molecules • Br I N Cl H O F I couldn't exist without you! Oh, Ha Ha!
Video • http://www.glencoe.com/sites/common_assets/science/cmc/cim/animations/ch8_1.swf
Lewis Structures and Octet • Practice by drawing • H2 • O2 • N2 • H2O • CO2 - + + -
Lewis Structures and Octet • Practice by drawing • H2 - + + -
Lewis Structures and Octet • Practice by drawing O2 σ - - - - - - - - - - - + - - - - - + + + - - - - - - - - π
Strength of Covalent Bonds • Strength depends on distance of the atoms from each other • With more bonds comes stronger bonds • O2 is stronger than H2
Bonds and Energy • Endothermic reactions require additional energy for bonds to break • Exothermic reactions release energy when the bonds break (spontaneous)
Can you… • Apply the octet rule to atoms that form covalent bonds. • Describe the formation of single, double, and triple covalent bonds. • Contrast sigma and pi bonds. • Relate the strength of a covalent bond to its bond length and bond dissociation energy.
Section 8.2 Chemistry Matter & Change Naming Molecules
Specific rules are used when naming binary molecular compounds, binary acids and oxyacids 8.2 Main Idea
objectives • Translate molecular formulas into binary molecular names. • Name acidic solutions.
Review Vocabulary & Concepts • Ionic bond • Covalent bond • Formula unit • Oxyanion • Naming ionic substances • Molecule
New Vocabulary & Concepts • Oxyacid • Binary acid
Naming Binary Molecular Compounds • Name the first element using the entire name of the element. • The second element in the formula is named using the root and suffix “-ide.” • Prefixes are used to indicate the numbers of each element.
Naming Binary Molecular Compounds • Exceptions to the rules: • The first element never uses “mono-” • There is an understood 1 if nothing is specified. • Awkward vowels can be dropped
Naming Binary Molecular Compounds Exception • The first element never uses “mono-” • There is an understood 1 if nothing is specified. • CO2 is carbon dioxide not monocarbon dioxide • CO is carbon monoxide, not monocarbon monoxide
Naming Binary Acids • The first word has the prefix “hydro-” followed by the root of the second element followed by “-ic” • The second word is “acid” • HCl- hydrochloric acid
Practice Naming Binary Acids • Hydrobromic acid • Hydrophosphic acid • Hydrosulfuric acid • HF • H2Se • HI
Naming Oxyacids • First word consists of the root of the oxyanion (with prefixes if needed) followed by a suffix as specified • If oxyanion ends in • The second word is always “acid.”
Naming Oxyacids • First word consists of the root of the oxyanion (with prefixes if needed) followed by a suffix as specified • The second word is always “acid.”
Look at the formula of the molecule Is it an acid? No Yes Is there oxygen present in the compound? Name the first element using a prefix if necessary Name the second element indicating the number of atoms and changing the suffix to –ide. Yes No Hydro(root) ic acid Root + -ic if the anion ends in –ate, or Root + -ous if the anion ends in –ite, then acid
Can You • Translate molecular formulas into binary molecular names. • Name acidic solutions.
Section 8.3 Chemistry Matter & Change Molecular Structure
Structural formulas show the relative positions of atoms within a molecule. 8.3 Main Idea
objectives • List the basic steps used to draw Lewis structures. • Explain why resonance occurs and identify resonance structures. • Identify three exceptions to the octet rule and name molecules in which these exceptions occur.
Review Vocabulary & Concepts • Ionic bond • Covalent bond • Lewis-dot structure • Octet
New Vocabulary & Concepts • Structural formula • Resonance • Coordinate covalent bond • Space filling model • Ball and stick model
Molecular Structures • Many different ways to depict the same thing • Molecular formula • Structural formula • Lewis Structure • Space-filling model • Ball-and-stick model
Molecular Formula • Indicates number of each element in a molecule • H2O • C6H12O6 • NH3
Structural Formulas • Molecular model that shows the relative positions of the atoms O H H
Lewis Structure • Shows shared electrons and lone pairs • Shared pairs are usually depicted as lines • Lone pairs may be lines or dots