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Chapter 10 Lecture Basic Chemistry Fourth Edition Chapter 10 Properties of Solids and Liquids 10.1 Electron-Dot Formulas Learning Goal Draw the electron-dot formulas for molecular compounds or polyatomic ions with multiple bonds and show resonance structures. © 2014 Pearson Education, Inc. Chapter 10 Readiness Core Chemistry Skills • Using Significant Figures in Calculations (2.4) • Using Conversion Factors (2.7) • Classifying Matter (3.1) • Identifying Physical and Chemical Changes (3.2) • Using Energy Units (3.4) • Using the Heat Equation (3.4) • Drawing Electron-Dot Symbols (5.6) © 2014 Pearson Education, Inc. Electron-Dot Symbols Electron-dot symbols show • one to four valence electrons as single dots on the sides of an atomic symbol • five to eight valence electrons with one or more pairs of dots on the sides of an atomic symbol © 2014 Pearson Education, Inc. Electron-Dot Symbols of Some Representative Elements © 2014 Pearson Education, Inc. Electron-Dot Formulas Electron-dot formulas show • the sequence of bonded atoms in a molecule or polyatomic ion • the bonding pairs of electrons shared between atoms • the nonbonding or unshared (lone pairs) of electrons • the central atom bonded to other atoms © 2014 Pearson Education, Inc. Lone Pairs and Bonding Pairs The electron-dot formula for H O H H2O contains: • 8 valence electrons (6 from O plus 1 from each hydrogen atom) • O as the central atom • two bonding pairs (between the H and O atoms) and two lone pairs (on the O atom) © 2014 Pearson Education, Inc. Drawing Electron-Dot Formulas © 2014 Pearson Education, Inc. Writing Electron-Dot Formulas Draw the electron-dot formula for PCl3, phosphorus trichloride, used to prepare insecticides and flame retardants. Step 1 Determine the arrangement of atoms. The central atom is P; there is only one P atom. © 2014 Pearson Education, Inc. Writing Electron-Dot Formulas Draw the electron-dot formula for PCl3. Step 2 Determine the total number of valence electrons. © 2014 Pearson Education, Inc. Writing Electron-Dot Formulas Draw the electron-dot formula for PCl3. Step 3 Attach each bonded atom to the central atom with a pair of electrons. Bonding electrons can also be represented by a line. © 2014 Pearson Education, Inc. Writing Electron-Dot Formulas Draw the electron-dot formula for PCl3. Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. © 2014 Pearson Education, Inc. Writing Electron-Dot Formulas Draw the electron-dot formula for PCl3. Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. Use the remaining 20 e− as lone pairs on P and Cl atoms to complete octets. © 2014 Pearson Education, Inc. Learning Check Write the electron-dot formula for ClO3−. © 2014 Pearson Education, Inc. Solution Draw the electron-dot formula for ClO3−. Step 1 Determine the arrangement of atoms. The central atom is Cl; there is only one Cl atom. O O Cl O © 2014 Pearson Education, Inc. - − Solution Draw the electron-dot formula for ClO3− . Step 2 Determine the total number of valence electrons. Element Cl O © 2014 Pearson Education, Inc. Group 7A (17) 6A (16) Atoms 1 Cl 3O Valence Electrons × 7 e− × 6 e− Total = 7− = 18 e− Solution Draw the electron-dot formula for ClO3−. Step 3 Attach each bonded atom to the central atom with a pair of electrons. Bonding electrons can also be represented by a line. O O Cl O © 2014 Pearson Education, Inc. -− O O Cl O -− Solution Draw the electron-dot formula for ClO3− . Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. © 2014 Pearson Education, Inc. Solution Draw the electron-dot formula for ClO3−. Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. Use the remaining 20 e− as lone pairs on Cl and O atoms to complete octets. O O Cl O © 2014 Pearson Education, Inc. - − O O Cl O - − Multiple Bonds Multiple bonds form when there are not enough valence electrons to complete 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. © 2014 Pearson Education, Inc. Multiple Bonds, CO2 In carbon dioxide, CO2, octets are achieved by sharing two pairs of electrons between atoms; this is called a double bond. © 2014 Pearson Education, Inc. Multiple Bonds, N2 In nitrogen, N2, octets are achieved by sharing three pairs of electrons between atoms; this is called a triple bond. © 2014 Pearson Education, Inc. Resonance Structures Resonance structures • may be written for molecules or polyatomic ions with multiple bonds • consist of two or more electron-dot formulas for the same arrangement of atoms • are shown with a double-headed arrow • are written by changing the location of a double bond © 2014 Pearson Education, Inc. Resonance Structures, O3 Molecules that contain multiple bonds may contain more than one electron-dot formula. Ozone, O3 is a component in the stratosphere that protects us from the ultraviolet rays of the Sun. © 2014 Pearson Education, Inc. Resonance Structures, O3 The electron-dot formula for O3 contains • 18 valence electrons • 3 bonding pairs • 5 lone pairs It is possible to draw two electron-dot structures or resonance structures for O3. © 2014 Pearson Education, Inc. Learning Check Carbonate has three resonance structures. If the following is one, what are the other two? - 2 2− O O © 2014 Pearson Education, Inc. C O Solution Carbonate has three resonance structures. If the following is one, what are the other two? The double bond can also exist between the other two oxygen atoms and the central carbon atom. - 2 O O © 2014 Pearson Education, Inc. C O - 2 O O C O - 2 O O C O Learning Check Draw the two resonance structures for SO2. © 2014 Pearson Education, Inc. Solution Draw the two resonance structures for SO2. Step 1 Determine the arrangement of atoms. The central atom is S, because there is only one S atom in the formula. S O © 2014 Pearson Education, Inc. O Solution Draw the two resonance structures for SO2. Step 2 Determine the total number of valence electrons. Element S O © 2014 Pearson Education, Inc. Group 6A (16) 6A (16) Atoms 1S 2O Valence Electrons × 6 e− × 6 e− Total = 6e− = 12e− Solution Draw the two resonance structures for SO2. Step 3 Attach each bonded atom to the central atom with a pair of electrons. S O © 2014 Pearson Education, Inc. O Solution Draw the two resonance structures for SO2. Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. © 2014 Pearson Education, Inc. Solution Draw the two resonance structures for SO2. Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. Use the remaining 14 e− as lone pairs on S and O atoms. To complete the octet on S, make a double bond. O © 2014 Pearson Education, Inc. S O O S O Exceptions to the Octet Rule Exceptions to the octet rule include: • hydrogen, H, only gets a single bond • boron, B, has only 3 electrons around it to form bonds • compounds of P, S, Cl, Br, and I can have expanded octets with 10, 12, or even 14 valence electrons around them © 2014 Pearson Education, Inc. Using Valence Electrons to Draw ElectronDot Formulas © 2014 Pearson Education, Inc.