1. 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.

2. 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)

3. 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

4. Electron-Dot Symbols of Some Representative Elements

5. 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

6. 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)

7. Drawing Electron-Dot Formulas

8. 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.

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

10. 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.

11. 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.

12. 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.

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

14. 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. −

15. 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−

16. 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. − −

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

18. 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. − −

19. 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.

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

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

22. 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

23. 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.

24. 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.

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

26. 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.

27. Learning Check
Draw the two resonance structures for SO2.

28. 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.

29. 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−

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

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

32. 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.

33. 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

34. Using Valence Electrons to Draw Electron-Dot Formulas