1. 1 Chapter 10 Molecular Structure: Liquids and Solids 10.2 Electron-Dot Formulas Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

2. 2 Number of Covalent Bonds The number of covalent bonds can be determined from the number of electrons needed to complete an octet. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Table 10.1

3. 3 Electron-Dot Formulas Electron-dot formulas show The order of bonded atoms in a covalent compound. The bonding pairs of electrons between atoms. The unshared (lone) valence electrons. A central atom with an octet. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

4. 4 Guide to Writing Electron-Dot Formulas STEP 1 Determine the arrangement of atoms. STEP 2 Add the valence electrons from all the atoms. STEP 3 Attach the central atom to each bonded atom using one pair of electrons. STEP 4 Add remaining electrons as lone pairs to complete octets (2 for H atoms). STEP 5 If octets are not complete, form one or more multiple bonds.

5. 5 Electron-Dot Formula of SF 2 Write the electron-dot formula for SF 2. STEP 1 Determine the atom arrangement. S is the central atom. F S F STEP 2 Total the valence electrons for 1S and 2F. 1S(6e - ) + 2F(7e - ) = 20e -

6. 6 Electron-Dot Formula SF 2 STEP 3 Attach F atoms to S with one electron pair. F : S : F Calculate the remaining electrons. 20e - - 4 e - = 16e - left STEP 4 Complete the octets of all atoms by placing remaining e - as 8 lone pairs to complete octets.             : F : S : F : or : F─S─F :            

7. 7 Electron-Dot Formula ClO 3 - Write the electron-dot formula for ClO 3 −. STEP 1 Determine atom arrangement. Cl is the central atom. O − O Cl O STEP 2 Add all the valence electrons for 1Cl and 3O plus 1e - for negative charge on the ion. 1Cl(7e - ) + 3 O(6e - ) + 1e − = 26e -

8. 8 Electron-Dot Formula ClO 3 - STEP 3 Attach each O atom to Cl with one electron pair. O −   O : Cl : O Calculate the remaining electrons. 26e - - 6 e - = 20e - left

9. 9 Electron-Dot Formula ClO 3 - STEP 4 Complete the octets of all atoms by placing the remaining 20 e - as 10 lone pairs to complete octets.   −   − : O : : O :         │   : O : Cl : O : or : O─Cl─O :            

10. 10 Multiple Bonds 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.

11. 11 Multiple Bonds in N 2 In nitrogen N 2, Octets are achieved by sharing three pairs of electrons, which is a triple bond. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

12. 12 Electron-Dot Formula of CS 2 Write the electron-dot formula for CS 2. STEP 1 Determine the atom arrangement. The C atom is the central atom. S C S STEP 2 Total the valence electrons for 1C and 2S. 1C(4e - ) + 2S(6e - ) = 16e -

13. 13 Electron-Dot Formula CS 2 STEP 3 Attach each S atom to C with electron pairs. S : C : S Calculate the remaining electrons. 16e - - 4 e - = 12e - left

14. 14 Electron-Dot Formula CS 2 STEP 4 Attach 12 remaining electrons as 6 lone pairs to complete octets..... : S : C : S :.... STEP 5 To complete octets, move two lone pairs between C and S atoms to give two double bonds......... : S : : C : : S : or : S = C = S : `

15. 15 Some Electron-Dot Formulas Table 10.2 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

16. 16 Resonance structures are Two or more electron-dot formulas for the same arrangement of atoms. Related by a double-headed arrow. Written by changing location of a double bond from the central atom to a different attached atom. Sometimes written as a hybrid resonance structure. Resonance Structures

17. 17 Resonance structures for NO 3 − are −   −   − : O : : O : : O : ║ │ │ N N N : O : : O : : O : : O : : O : : O :         Resonance Structures

18. 18 Carbonate has three resonance structures. If the following is one, what are the other two? 2- :O: C :O: :O:     Learning Check

19. 19 Carbonate has three resonance structures. If the following is one, what are the other two? 2−   2−   2− :O: :O: :O: │ │ C C C :O : :O: :O: :O : :O: :O:         Solution

20. 20 Cyanate ion NCO − has three resonance structures. STEP 1 Write the arrangement of atoms. N C O − STEP 2 Count the valence electrons. 1N(5e − ) + 1C(4e − ) + 1 O(6e − ) + charge (1e − ) = 16e − STEP 3 Connect bonded atoms by single electron pairs. N: C :O − 4e − used Determine the remaining electrons. 16e − - 4e − = 12e − Writing Resonance Structures

21. 21 STEP 4 Add 12 remaining electrons as 6 lone pairs     − : N─C─O :     STEP 5 Form double or triple bonds to make octets     −   −   − : N=C=O : : N─C  O : : N  C─O :     Writing Resonance Structures

22. 22 Write two resonance structures for nitrite NO 2 −. Learning Check

23. 23 NO 2 − = 18 e − Electron-dot formula       − : O─N─O :     Using a double bond to complete octets gives two resonance structures       −       − :O=N─O: :O─N=O:     Solution