TABLE 1.4 How to Write Lewis Structures Step Illustration 1. The molecular formula and the connectivity are Methyl nitrite has the molecular formula CH3No2. All determined experimentally and are included hydrogens are bonded to carbon, and the order of among the information given in the statement of atomic connections is CONO the problem 2. Count the number of valence electrons available Each hydrogen contributes 1 valence electron, car or a neutral molecule this is equal to the sum of on contributes 4, nitrogen contributes 5, and each the valence electrons of the constituent atoms oxygen contributes 6 for a total of 24 in CH3 NO 3. Connect bonded atoms by a shared electron pair For methyl nitrite we write the partial structure ond()represented by a dash(-) 4. Count the number of electrons in shared electron The partial structure in step 3 contains 6 bonds pair bonds (twice the number of bonds), and sub- equivalent to 12 electrons. Since CH3No, contains 24 tract this from the total number of electrons to electrons. 12 more electrons need to be added give the number of electrons to be added to com- plete the structure 5. Add electrons in pairs so that lany atoms as With 4 bonds, carbon already has 8 electrons. The re possible have 8 electrons(Hydrogen is limited to 2 maining 12 electrons are added as indicated. Both electrons. )When the number of electrons is insuffi- oxygens have 8 electrons, but nitrogen(less electro- cient to provide an octet for all atoms, assign elec- negative than oxygen) has only 6. trons to atoms in order of decreasing electronega- tivity. H-C-0—N-O H 6. If one or more atoms have fewer than 8 electrons, An electron pair on the terminal oxygen is shared se unshared pairs on an adjacent atom to form a with nitrogen to give a double bon double(or triple)bond d to complete the octet H|C|H The structure shown is the best (most stable) Lewis structure for methyl nitrite. All atoms except hydro- gen have 8 electrons(shared unshared) in their va lence shell 7. Calculate formal charges None of the atoms in the lewis structure shown in step 6 possesses a formal charge. An alternative Lewis structure for methyl nitrite Ithough it satisfies the octet rule, is less stable than the one shown in step 6 because it has a separation of positive charge from negative charge Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteTABLE 1.4 How to Write Lewis Structures Step 1. The molecular formula and the connectivity are determined experimentally and are included among the information given in the statement of the problem. 2. Count the number of valence electrons available. For a neutral molecule this is equal to the sum of the valence electrons of the constituent atoms. 6. If one or more atoms have fewer than 8 electrons, use unshared pairs on an adjacent atom to form a double (or triple) bond to complete the octet. 7. Calculate formal charges. 4. Count the number of electrons in shared electron pair bonds (twice the number of bonds), and sub￾tract this from the total number of electrons to give the number of electrons to be added to com￾plete the structure. 5. Add electrons in pairs so that as many atoms as possible have 8 electrons. (Hydrogen is limited to 2 electrons.) When the number of electrons is insuffi￾cient to provide an octet for all atoms, assign elec￾trons to atoms in order of decreasing electronega￾tivity. Illustration Methyl nitrite has the molecular formula CH3NO2. All hydrogens are bonded to carbon, and the order of atomic connections is CONO. Each hydrogen contributes 1 valence electron, car￾bon contributes 4, nitrogen contributes 5, and each oxygen contributes 6 for a total of 24 in CH3NO2. An electron pair on the terminal oxygen is shared with nitrogen to give a double bond. For methyl nitrite we write the partial structure The structure shown is the best (most stable) Lewis structure for methyl nitrite. All atoms except hydro￾gen have 8 electrons (shared
unshared) in their va￾lence shell. None of the atoms in the Lewis structure shown in step 6 possesses a formal charge. An alternative Lewis structure for methyl nitrite, although it satisfies the octet rule, is less stable than the one shown in step 6 because it has a separation of positive charge from negative charge. The partial structure in step 3 contains 6 bonds equivalent to 12 electrons. Since CH3NO2 contains 24 electrons, 12 more electrons need to be added. With 4 bonds, carbon already has 8 electrons. The re￾maining 12 electrons are added as indicated. Both oxygens have 8 electrons, but nitrogen (less electro￾negative than oxygen) has only 6. H±C±O±N±O H W W H 3. Connect bonded atoms by a shared electron pair bond ( ) represented by a dash (±). H±C±O±N±O H W W H H±C±O±NœO H W W H H±C±OœN±O
H W W H Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website