Chapter 5 Compounds and Their Bonds

1. Chapter 5Compounds and Their Bonds 5.5Covalent Compounds

2. Covalent Bonds Covalent bonds form • when atoms share electrons to complete octets • between two nonmetal atoms from from Groups 4A(14), 5A(15), 6A(16), and 7A(17)

3. Formation of H2 In the simplest covalent molecule, H2, the H atoms • increase attraction as they move closer • share electrons • form a covalent bond

4. Formation of H2 (continued)

5. Forming Octets in Molecules In a fluorine (F2)molecule, each F atom • shares one electron • acquires an octet

6. Diatomic Elements • These elements share electrons to form diatomic, covalent molecules.

7. Learning Check What is the name of each of the following diatomic molecules? H2 _______________ N2 _______________ Cl2 _______________ O2 _______________ I2 _______________

8. Solution What is the name of each of the following diatomic molecules? H2 hydrogen N2 nitrogen Cl2 chlorine O2 oxygen I2 iodine

9. Carbon Forms 4 Covalent Bonds In a methane (CH4) molecule, • the central C atom shares 4 electrons to attain an octet • each H atom shares 1 electron with the carbon atom to become stable like He

10. Electron-Dot Formula for NH3 • In NH3, a N atom is bonded to three H atoms. • The electron-dot structure is written as: Lone pair of electrons

11. Number of Covalent Bonds The number of covalent bonds can be determined from the number of electrons needed to complete an octet.

12. Electron-Dot Formulas and Models of Some Covalent Compounds

13. Guide to Writing Electron-Dot Formulas

14. Guide to Writing Electron-Dot Formulas STEP 1 Determine the arrangement of atoms. STEP 2 Determine the total number of valence electrons. STEP 3 Attach each bonded atom to the central atom with a pair of electrons. STEP 4 Place remaining electrons as lone pairs to complete octets (2 for H atoms). STEP 5 If octets are not complete, form a multiple bond by converting a lone pair to a bonding pair.

15. Single and 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.

16. Electron-Dot Formula of CS2 Write the electron-dot formula for CS2. STEP 1Determine the atom arrangement. The C atom is the central atom. S C S STEP 2Determine the total number of valence electrons for 1C and 2S. 1 C(4e–) + 2 S(6e–) = 16e–

17. Electron-Dot Formula of CS2 (continued) STEP 3Attach each S atom to the central C atom using one electron pair. S : C : S 16e– – 4e– = 12e– remaining STEP 4Attach 12 electrons as 6 lone pairs. .. .. : S : C : S :

18. Electron-Dot Formula of CS2 (continued) To complete octets, form one or more multiple bonds. Convert two lone pairs to bonding pairs between C and S atoms to make two double bonds.

19. A Nitrogen Molecule has A Triple Bond In a nitrogen molecule, N2, • each N atom shares 3 electrons • each N atom attains an octet • the sharing of 3 sets of electrons is a multiple bond called a triple bond

20. 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

21. Writing Resonance Structures Sulfur dioxide has two resonance structures. STEP 1Write the arrangement of atoms. O S O STEP 2Determine the total number of valence electrons. 1 S(6e−) + 2 O(6e−) = 18e− STEP 3Connect bonded atoms by single electron pairs. O : S : O4e− used 18e− – 4e− = 14e−remaining

22. Writing Resonance Structures (continued) STEP 4Add 14 remaining electrons as 7 lone pairs. STEP 5Form a double bond to complete octets. Two resonance structures are possible.

23. Learning Check FNO2, a rocket propellant, has two resonance structures. One is shown below. What is the other resonance structure?

24. Solution FNO2, a rocket propellant, has two resonance structures. One is shown below. What is the other resonance structure?