Formal charge definition

This definition of formal charge, Q, leads to the following equation... 

Unfortunately, many compounds contain bonds that are a mixture of ionic and covalent. In such a case, a formal charge as written is unlikely to represent the actual number of charges gained or lost. For example, the complex ferrocyanide anion [Fe(CN)6]4- is prepared from aqueous Fe2+, but the central iron atom in the complex definitely does not bear a +2 charge (in fact, the charge is likely to be nearer +1.5). Therefore, we employ the concept of oxidation number. Oxidation numbers are cited with Roman numbers, so the oxidation number of the iron atom in the ferrocyanide complex is +11. The IUPAC name for the complex requires the oxidation number we call it hexacyanoferrate (II). 

In the examples we have been looking at till now in this section it has been pretty clear which atom would be the central atom. For some molecules or composite ions however it is not always so obvious which atom that is the central atom. In order to be able to write down the Lewis structure for such a molecule or composite ion, we have to introduce the concept of formal charge. The formal charge of an atom in a molecule or composite ion has the following definition ... 

However, it is still a formal, impractical definition since we know neither the exact positions of protons nor the nuclear charge density. 

DEFINITIONS VALENCE, OXIDATION STATE, FORMAL CHARGE, AND COORDINATION NUMBER... 

Although the entire hydronium ion carries a positive charge, we can ask, Which atom, in a formal sense, bears the charge To determine formal charge, we consider each atom to own all of its unshared electrons plus only half of its shared electrons (one electron from each covalent bond). We then subtract this total from the number of valence electrons in the neutral atom to get the formal charge. This definition can be expressed in equation form as follows ... 

There are important differences between the two concepts which should be appreciated. Oxidation state is a formal charge on an atom which is in combination with one of the very electronegative atoms, i.e. F or O, in which their oxidation states are deemed to be -1 and -2, respectively. For example, in MgF, and MgO the oxidation state of the magnesium is +2 (i.e. II in the Roman numerals conventionally used to indicate oxidation states Mg ) and equal to the charge on the Mg- ions in those compounds. In ionic compounds there are no electron-pair bonds so the strict definition of valency, given above, does not apply. 

Definitions. Define and illustrate the following terms (a) octet rule, (b) Lewis symbol, (c) ionic bond, (d) covalent bond, (e) crystal lattice energy, (f) Iree radical, (g) network covalent compound, (h) electronegativity, (i) polar molecule, (j) dipole moment, (k) formal charge, (1) oxidation number, (m) hydrogen bond, (n) dipole-dipole attraction, (o) London forces. 

Recall that one definition of a strong base is A molecule with a -1 formal charge localized on an H, C, N, or O atom. Constmct an explanation for why bicarbonate ion is NOT a strong base. 

Recall our definition of a strong base a molecule with a -1 formal charge localized on C, N or O. 

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