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.

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)

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

Electron-Dot Symbols of Some Representative Elements

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

Lone Pairs and Bonding Pairs The electron-dot formula for 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)

Drawing Electron-Dot Formulas

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.

Writing Electron-Dot Formulas Draw the electron-dot formula for PCl3. Step 2 Determine the total number of valence electrons.

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.

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.

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.

Learning Check Write the electron-dot formula for ClO3−.

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. −

Solution Draw the electron-dot formula for ClO3− . Step 2 Determine the total number of valence electrons. Element Group Atoms Valence Electrons Total Cl 7A (17) 1 Cl × 7 e− = 7 − O 6A (16) 3 O × 6 e− = 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. − −

Solution Draw the electron-dot formula for ClO3− . Step 4 Place the remaining electrons using single or multiple bonds to complete the octets.

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. − −

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.

Multiple Bonds, CO2 In carbon dioxide, CO2, octets are achieved by sharing two pairs of electrons between atoms; this is called a double bond.

Multiple Bonds, N2 In nitrogen, N2, octets are achieved by sharing three pairs of electrons between atoms; this is called a triple bond.

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

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.

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.

Learning Check Carbonate has three resonance structures. If the following is one, what are the other two? 2−

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.

Learning Check Draw the two resonance structures for SO2.

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.

Solution Draw the two resonance structures for SO2. Step 2 Determine the total number of valence electrons. Element Group Atoms Valence Electrons Total S 6A (16) 1 S × 6 e− = 6e− O 2 O = 12e−

Solution Draw the two resonance structures for SO2. Step 3 Attach each bonded atom to the central atom with a pair of electrons.

Solution Draw the two resonance structures for SO2. Step 4 Place the remaining electrons using single or multiple bonds to complete the octets.

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.

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

Using Valence Electrons to Draw Electron-Dot Formulas