General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 5.5 Covalent Compounds: Sharing Electrons Chapter 5 Compounds and Their Bonds © 2013 Pearson Education, Inc. Lectures

© 2013 Pearson Education, Inc. Chapter 5, Section 5 2 Covalent bonds form when atoms of nonmetals share electrons to complete octets. Valence electrons are not transferred, but shared to achieve stability. Covalent Bonds

© 2013 Pearson Education, Inc. Chapter 5, Section 5 3 Formation of H 2 In the simplest covalent molecule, H 2, the H atoms  increase attraction as they move closer.  share electrons to achieve a stable configuration.  form a covalent bond.

© 2013 Pearson Education, Inc. Chapter 5, Section 5 4 Formation of H 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 5 Electron-Dot Formulas of Covalent Molecules In a fluorine (F 2 ) molecule, the F atoms  share one of their valence electrons.  acquire an octet.  form a covalent bond.

© 2013 Pearson Education, Inc. Chapter 5, Section 5 6 Elements That Exist as Diatomic Molecules These seven elements share electrons to form diatomic, covalent molecules.

© 2013 Pearson Education, Inc. Chapter 5, Section 5 7 What is the name of each of the following diatomic molecules? H 2 _______________ N 2 _______________ Cl 2 _______________ O 2 _______________ I 2 _______________ Learning Check

© 2013 Pearson Education, Inc. Chapter 5, Section 5 8 What is the name of each of the following diatomic molecules? H 2 hydrogen N 2 nitrogen Cl 2 chlorine O 2 oxygen I 2 iodine Solution

© 2013 Pearson Education, Inc. Chapter 5, Section 5 9 The number of covalent bonds a nonmetal forms is usually equal to the number of electrons it needs to acquire a stable electron configuration. Typical bonding patterns for some nonmetals are shown in the table below. Bonding Patterns of Some Nonmetals

© 2013 Pearson Education, Inc. Chapter 5, Section 5 10 Electron-Dot Formulas for Some Covalent Compounds

© 2013 Pearson Education, Inc. Chapter 5, Section 5 11 Guide to Drawing Electron-Dot Formulas

© 2013 Pearson Education, Inc. Chapter 5, Section 5 12 Step 1 Determine the arrangement of atoms. In NH 3, N is the central atom and is bonded to three H atoms. Step 2 Determine the total number of valence electrons. Total valence electrons for NH 3 = 8 e− Draw the Electron-Dot Formula for NH 3

© 2013 Pearson Education, Inc. Chapter 5, Section 5 13 Step 3 Attach each bonded atom to the central atom with a pair of electrons. Draw the Electron-Dot Formula for NH 3

© 2013 Pearson Education, Inc. Chapter 5, Section 5 14 Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. 8 valence e − − 6 bonding e − = 2 e − remaining Use the remaining 2 e − to complete the octet around the N atom. Draw the Electron-Dot Formula for NH 3

© 2013 Pearson Education, Inc. Chapter 5, Section 5 15 Learning Check Draw the electron-dot formula for CCl 4.

© 2013 Pearson Education, Inc. Chapter 5, Section 5 16 Step 1 Determine the arrangement of atoms. In CCl 4, C is the central atom and is bonded to four Cl atoms. Solution

© 2013 Pearson Education, Inc. Chapter 5, Section 5 17 Step 2 Determine the total number of valence electrons. Total valence electrons for Solution

© 2013 Pearson Education, Inc. Chapter 5, Section 5 18 Step 3 Attach each bonded atom to the central atom with a pair of electrons. Solution

© 2013 Pearson Education, Inc. Chapter 5, Section 5 19 Step 4 Place the remaining electrons, using single or multiple bonds to complete the octets. 32 valence e − − 8 bonding e − = 24 e − remaining Use the remaining 24 e − to complete the octets around the Cl atoms. Solution

© 2013 Pearson Education, Inc. Chapter 5, Section 5 20 Exceptions to the Octet Rule Not all atoms have octets.  Some can have less than an octet, such as H, which requires only 2 electrons, B, which requires only 3 electrons, and Be, which requires only 4 electrons.  Some can have expanded octets, such as P, which can have 10 electrons, S, which can have 12 electrons, and Cl, Br and I, which can have 14 electrons

© 2013 Pearson Education, Inc. Chapter 5, Section 5 21 Single and Multiple Bonds In many covalent compounds, atoms share two or three pairs of electrons to complete their octets.  In a single bond, one pair of electrons is shared.  In a double bond, two pairs of electrons are shared.  In a triple bond, three pairs of electrons are shared.

© 2013 Pearson Education, Inc. Chapter 5, Section 5 22 Step 1 Determine the arrangement of atoms. In CS 2, C is the central atom and is bonded to two S atoms. Draw the Electron-Dot Formula for CS 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 23 Step 2 Determine the total number of valence electrons. Total valence electrons for Draw the Electron-Dot Formula for CS 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 24 Step 3 Attach each bonded atom to the central atom with a pair of electrons. A pair of bonding electrons (single bond) is placed between each S atom and the central C atom. Draw the Electron-Dot Formula for CS 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 25 Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. 16 valence e − - 4 bonding e − = 12 e − remaining The remaining 12 electrons are placed as six lone pairs of electrons on both S atoms. However, this does not complete the octet for the C atom. Draw the Electron-Dot Formula for CS 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 26 Step 4 Continued: Double and Triple Covalent Bonds: To complete the octet for the C atom, it needs to share an additional lone pair from each of the S atoms, forming a double bond with each S atom. Draw the Electron-Dot Formula for CS 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 27 A Nitrogen Molecule has a Triple Bond In a nitrogen molecule, N 2,  each N atom shares 3 electrons,  each N atom attains an octet, and  the sharing of 3 sets of electrons is called a triple bond.

© 2013 Pearson Education, Inc. Chapter 5, Section 5 28 Resonance structures are  two or more electron-dot formulas for the same arrangement of atoms.  related by a double-headed arrow ( ).  written by changing the location of a double bond between the central atom and a different attached atom. Resonance Structures

© 2013 Pearson Education, Inc. Chapter 5, Section 5 29 Sulfur dioxide has two resonance structures. Step 1 Determine the arrangement of atoms. In SO 2, the S atom is the central atom. O S O Step 2 Determine the total number of valence electrons. Total valence electrons for Writing Resonance Structures for SO 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 30 Step 3 Attach each bonded atom to the central atom with a pair of electrons. Writing Resonance Structures for SO 2 O S O O S O or

© 2013 Pearson Education, Inc. Chapter 5, Section 5 31 Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. The remaining 14 electrons are drawn as lone pairs of electrons to complete the octets of the O atoms, but not the S atom. Writing Resonance Structures for SO 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 32 Step 4 Continued: To complete the octet for S, an additional lone pair from one of the O atoms is shared to form a double bond. Because the shared lone pair of electrons can come from either O atom, two resonance structures can be drawn. Writing Resonance Structures for SO 2

© 2013 Pearson Education, Inc. Chapter 5, Section 5 33 FNO 2, a rocket propellant, has two resonance structures. One is shown below. What is the other resonance structure? Learning Check

© 2013 Pearson Education, Inc. Chapter 5, Section 5 34 FNO 2, a rocket propellant, has two resonance structures. One is shown below. What is the other resonance structure? Solution