Chapter 6 Covalent Compounds Table of Contents Section 1 Covalent Bonds Section 2 Drawing and Naming Molecules Section 3 Molecular Shapes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Bellringer • Make a list of the elements that form ionic bonds. Note that most ionic bonds contain a metal and a nonmetal. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Objectives • Explain the role and location of electrons in a covalent bond. • Describe the change in energy and stability that takes place as a covalent bond forms. • Distinguish between nonpolar and polar covalent bonds based on electronegativity differences. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Objectives, continued • Compare the physical properties of substances that have different bond types, and relate bond types to electronegativity differences. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Sharing Electrons • When an ionic bond forms, electrons are rearranged and are transferred from one atom to another to form charged ions. • In another kind of change involving electrons, the neutral atoms share electrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Sharing Electrons, continued Forming Molecular Orbitals • A covalent bond is a bond formed when atoms _______________one or more pairs of electrons. • The shared electrons move within a space called a molecular orbital. • A molecular orbital is the ______________of high probability that is occupied by an individual electron as it travels with a wavelike motion in the threedimensional space around one of two or more associated nuclei. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Formation of a Covalent Bond Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Visual Concepts Chemical Bond Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Energy and Stability Energy Is Released When Atoms Form a Covalent Bond Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Energy and Stability, continued Potential Energy Determines Bond Length • When two bonded hydrogen atoms are at their lowest potential energy, the distance between them is 75 pm. • The ___________________is the distance between two bonded atoms at their minimum potential energy. • However, the two nuclei in a covalent bond vibrate back and forth. The bond length is thus the average ______________________between the two nuclei. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Visual Concepts Bond Length Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Energy and Stability, continued Bonded Atoms Vibrate, and Bonds Vary in Strength • The bond length is the average distance between two nuclei in a covalent bond. • At a bond length of 75 pm, the potential energy of H2 is –436 kJ/mol. • Thus 436 kJ of energy must be supplied to break the bonds in 1 mol of H2 molecules. • The energy required to break a bond between two atoms is the _________________________. • Bonds that have the higher bond energies (stronger bonds) have the shorter bond lengths. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Electronegativity and Covalent Bonding • In covalent bonds between two different atoms, the atoms often have different attractions for shared electrons. • Electronegativity values are a useful tool to predict what kind of bond will form. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Visual Concepts Electronegativity Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Electronegativity and Covalent Bonding, continued Atoms Share Electrons Equally or Unequally • When the electronegativity values of two bonding atoms are similar, bonding electrons are shared equally. • A covalent bond in which the bonding electrons in the molecular orbital are shared equally is a _________________________covalent bond. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Electronegativity and Covalent Bonding, continued Atoms Share Electrons Equally or Unequally, continued • When the electronegativity values of two bonding atoms are different, bonding electrons are shared unequally. • A covalent bond in which the bonding electrons in the molecular orbital are shared unequally is a _______________________covalent bond. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Predicting Bond Character from Electronegativity Differences Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Electronegativity and Covalent Bonding, continued Polar Molecules Have Positive and Negative Ends • In a polar covalent bond, the ends of the bond have opposite partial charges. • A molecule in which one end has a partial positive charge and the other end has a partial negative charge is called a ________________________. • In a polar covalent bond, the shared pair of electrons is not transferred completely. Instead, it is more likely to be found near the more electronegative atom. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Electronegativity and Covalent Bonding, continued Polar Molecules Have Positive and Negative Ends, continued • The symbol is used to mean partial. • + is used to show a partial _______________charge • – is used to show a partial _______________charge • example: H+F– • Because the F atom has a partial negative charge, the electron pair is more likely to be found nearer to the fluorine atom Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Visual Concepts Comparing Polar and Nonpolar Covalent Bonds Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Polarity Is Related to Bond Strength • In general, the greater the electronegativity difference, the greater the polarity and the stronger the bond. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Electronegativity and Bond Types • Differences in electronegativity values provide one model that can tell you which type of bond two atoms will form. • Another general rule states: • A covalent bond forms between two _______________. • An ionic bond forms between a _______________and a __________________. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 1 Covalent Bonds Properties of Substances Depend on Bond Type • The type of __________that forms (metallic, ionic, or covalent) determines the properties of the substance. • The difference in the strength of attraction between the basic units of ionic and covalent substances causes these types of substances to have different properties. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Properties of Substances with Metallic, Ionic, and Covalent Bonds Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Bellringer • Classify the following compounds according to the type of bonds they contain: • NO • CO • HF • NaCl • HBr • NaI Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Objectives • Draw Lewis structures to show the arrangement of valence electrons among atoms in molecules and polyatomic ions. • Explain the differences between single, double, and triple covalent bonds. • Draw resonance structures for simple molecules and polyatomic ions, and recognize when they are required. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Objectives, continued • Name binary inorganic covalent compounds by using prefixes, roots, and suffixes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Lewis Electron-Dot Structures • _________________electrons are the electrons in the outermost energy level of an atom. • A _________________is a structural formula in which valence electrons are represented by dots. • In Lewis structures, dot pairs or dashes between two atomic symbols represent pairs in covalent bonds. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Lewis Electron-Dot Structures, continued Lewis Structures Show Valence Electrons • As you go from element to element across a period, you add a dot to each side of the element’s symbol. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Lewis Electron-Dot Structures, continued Lewis Structures Show Valence Electrons, continued • You do not begin to pair dots until all four sides of the element’s symbol have a dot. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Lewis Electron-Dot Structures, continued Lewis Structures Show Valence Electrons, continued • An element with an octet of valence electrons has a stable configuration. • The tendency of bonded atoms to have octets of valence electrons is called the _______________rule. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Lewis Electron-Dot Structures, continued Lewis Structures Show Valence Electrons, continued • When two chlorine atoms form a covalent bond, each atom contributes one electron to a shared pair. • An ____________________pair, or a lone pair, is a nonbonding pair of electrons in the valence shell of an atom. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Lewis Electron-Dot Structures, continued Lewis Structures Show Valence Electrons, continued • A _______________bond is a covalent bond in which two atoms share one pair of electrons • The electrons can pair in any order. However, any unpaired electrons are usually filled in to show how they will form a covalent bond. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Drawing Lewis Structures with Single Bonds Sample Problem A Draw a Lewis structure for CH3I. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Drawing Lewis Structures for Polyatomic Ions Sample Problem B 2SO Draw a Lewis structure for the sulfate ion, 4 . Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Multiple Bonds • For O2 to make an octet, each atom needs two more electrons. The two atoms share four electrons. • A _______________bond is a covalent bond in which two atoms share two pairs of electrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Multiple Bonds, continued • For N2 to make an octet, each atom needs three more electrons. The two atoms share six electrons. • A _______________bond is a covalent bond in which two atoms share three pairs of electrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Drawing Lewis Structures with Multiple Bonds Sample Problem C Draw a Lewis structure for formaldehyde, CH2O. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Resonance Structures • Some molecules, such as ozone, O3, cannot be represented by a single Lewis structure. • When a molecule has two or more possible Lewis structures, the two structures are called _______________structures. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Multiple Bonds, continued Naming Covalent Compounds • The first element named is usually the first one written in the formula. It is usually the less-electronegative element. • The second element named has the ending -ide. • Unlike the names for ionic compounds, the names for covalent compounds must often distinguish between two different molecules made of the same elements. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Naming Covalent Compounds, continued • This system of prefixes is used to show the number of atoms of each element in the molecule. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Section 2 Drawing and Naming Molecules Naming Covalent Compounds, continued • Prefixes can be used to show the numbers of each type of atom in diphosphorus pentasulfide. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 6 Visual Concepts Naming Compounds Using Numerical Prefixes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.