OXIDATION NUMBER (OXIDATION STATE)31 covalence. the efeds po the number of bonds allched to the atom in stion.Ir ence,more precisely called ionic valence,is the absolute charge on a monoatomic ion. Erample.The valence of Mg+is 2.The covalency of carbon in carbon monoxide. written as c=o:is 2,but in carbon dioxide,0=C=0:,it is 4.The ionic valence of both Ca and O in Cao is 2.The word"valence"standing alone is rather ambiguous and the more precise terms such as ionic valence.covalence,valence orbitals valence electron oxidation number,and formal charge are preferred. 2.10 OXIDATION NUMBER (OXIDATION STATE) A whole number assigned to an atom in a molecule representative of its formal ownership of the valence electrons around it.It is calculated by first assuming that all the electrons involved in bonding to the atom in question in the Lewis structure are assigned to either that atom or to its partner,if its partner is more electroneg ative.The number of valence electrons maining on the atom is then determined if the atom is bonded tot e sam lement asnaC-C bond re the bonding electrons are divided equally,and this number is then subtracted from the number of valence electrons associated with the atom in its elemental form.The difference between the two numbers is the oxidation number of the atom in question. Example.In the structures shown in Fig.2.10,the bonding electrons are removed with the more electronegative atoms as shown and the oxidation numbers for carbon (which can r ge from +4 to-4)and sulfur are displayed below the structure.The nber for oxygen in all these compounds is-2 and for the hydroger Figure 2.10.The oxidation numbers of carbon and sulfur in various compounds.The atoms numberscovalence, corresponds to the number of bonds attached to the atom in question. In the case of ions, the valence, more precisely called ionic valence, is the absolute charge on a monoatomic ion. Example. The valence of Mg

is 2. The covalency of carbon in carbon monoxide, written as is 2, but in carbon dioxide, , it is 4. The ionic valence of both Ca and O in CaO is 2. The word “valence” standing alone is rather ambiguous and the more precise terms such as ionic valence, covalence, valence orbitals, valence electrons, oxidation number, and formal charge are preferred. 2.10 OXIDATION NUMBER (OXIDATION STATE) A whole number assigned to an atom in a molecule representative of its formal ownership of the valence electrons around it. It is calculated by first assuming that all the electrons involved in bonding to the atom in question in the Lewis structure are assigned to either that atom or to its partner, if its partner is more electroneg￾ative. The number of valence electrons remaining on the atom is then determined if the atom is bonded to the same element, as in a C–C bond where the bonding electrons are divided equally, and this number is then subtracted from the number of valence electrons associated with the atom in its elemental form. The difference between the two numbers is the oxidation number of the atom in question. Example. In the structures shown in Fig. 2.10, the bonding electrons are removed with the more electronegative atoms as shown and the oxidation numbers for carbon (which can range from
4 to 4) and sulfur are displayed below the structure. The oxidation number for oxygen in all these compounds is 2 and for the hydrogen C O O C O OXIDATION NUMBER (OXIDATION STATE) 31 C O O C O S O O O O C C H H H H H C H H H C O H H H C O +2 +4 +6 H −2 H −4 O 0 H +2 ( ) ( ( ) ) ( ( ) ( ) ( ) ) ) ) ) ) ) ( ( ) ( ) Figure 2.10. The oxidation numbers of carbon and sulfur in various compounds. The atoms inside the curves between atoms are in each case the more electronegative atoms, and the bonding electrons are, therefore, associated with those atoms in determining the oxidation numbers. c02.qxd 5/17/2005 5:13 PM Page 31