Chapter 5 Compounds and Their Bonds 5.5 Covalent Compounds

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)

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

Formation of H2 (continued)

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

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

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

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

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

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

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

Electron-Dot Formulas and Models of Some Covalent Compounds

Guide to Writing Electron-Dot Formulas

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.

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.

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

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

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.

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

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

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

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

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

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