General Organic and Biological Chemistry Fourth Edition Karen

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

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 3

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

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 5

Elements That Exist as Diatomic Molecules These seven elements share electrons to form diatomic,

Learning Check What is the name of each of the following diatomic molecules? H

Solution What is the name of each of the following diatomic molecules? H 2

Bonding Patterns of Some Nonmetals 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 9

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

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

Draw the Electron-Dot Formula for NH 3 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− © 2013 Pearson Education, Inc. Chapter 5, Section 5 12

Draw the Electron-Dot Formula for NH 3 Step 3 Attach each bonded atom to

Draw the Electron-Dot Formula for NH 3 Step 4 Place the remaining electrons usingle 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 14

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

Solution Step 1 Determine the arrangement of atoms. In CCl 4, C is the

Solution Step 2 Determine the total number of valence electrons. Total valence electrons for

Solution Step 3 Attach each bonded atom to the central atom with a pair

Solution Step 4 Place the remaining electrons, usingle 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 19

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 20

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 21

Draw the Electron-Dot Formula for CS 2 Step 1 Determine the arrangement of atoms.

Draw the Electron-Dot Formula for CS 2 Step 2 Determine the total number of

Draw the Electron-Dot Formula for CS 2 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 24

Draw the Electron-Dot Formula for CS 2 Step 4 Place the remaining electrons usingle 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 25

Draw the Electron-Dot Formula for CS 2 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 26

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 27

Resonance Structures 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 28

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

Writing Resonance Structures for SO 2 Step 3 Attach each bonded atom to the

Writing Resonance Structures for SO 2 Step 4 Place the remaining electrons usingle 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 31

Writing Resonance Structures for SO 2 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. © 2013 Pearson Education, Inc. Chapter 5, Section 5 32