Codex @codex  0

Historical formulation name; composition is identified by pharmacopoeial edition.

Historical formulation name; composition is identified by pharmacopoeial edition.

For a chosen homogeneous composition ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_{4-\delta }$, assign formal oxidation states $+3$ to lanthanum, $+2$ to barium and $-2$ to oxygen. If $v$ is the mean formal copper oxidation state, charge neutrality requiresThe excess formal positive charge per copper relative to $+2$ is therefore $p_{\mathrm{formal}}=x-2\delta$. For stipulated $x=0.12$ and $\delta =0.01$, it is $0.10$; at $\delta =0.06$, it is zero. These are bookkeeping examples, not measurements of mobile carriers. The symbol $x$ here belongs to this declared formula, not the original mixed-phase recipe. A whole-pellet elemental ratio cannot simply be assigned to each constituent phase.

Charge neutrality alone does not locate holes. The lecture reviews oxygen-related carrier evidence and charge-$2e$ pairing from the Josephson effect and fluxoid and flux quantization in a superconductor. Pair charge does not establish phonon-mediated BCS theory for cuprate superconductors.^[ref]

For the routine examples here, assign all bonding electrons between different chemical elements to the more electronegative partner; divide bonding electrons between identical chemical elements equally. Retain each lone pair on its original chemical atom. Subtract the assigned valence electron count $N_i^{\mathrm{assigned}}$ from the neutral chemical atom's valence electron count $v_i$. The IUPAC convention uses Allen electronegativity, based on free-chemical atom valence electron energies. Close electronegativity comparisons and some reversibly bound chemical compounds require care beyond this simple rule.^[ref]

The examples explain exceptions to memorized rules:

These drawings record allocations, not molecular geometry or a physical process of breaking the chemical bonds. In particular, the O–O line in the molecular oxygen panel only marks the connection; it does not assert a complete Lewis structure or spin state.

A chemical compound containing iron; the oxidation state and associated ligands distinguish medicinal preparations.

The +2 oxidation state of iron; the aqueous cation is commonly represented by $\mathrm{F}{\mathrm{e}}^{2+}$.

The +3 oxidation state of iron; the aqueous cation is commonly represented by $\mathrm{F}{\mathrm{e}}^{3+}$.

A class of iron–oxygen chemical compounds, including oxides with different iron oxidation states.

An iron phosphate; a precise description must state the oxidation state and hydration or mixed composition.

The +2 oxidation state of lead. The actual aqueous species can depend on pH, hydrolysis and ligands; a bare ionic formula is an analytical shorthand.

The +2 oxidation state of Mercury. The actual aqueous species can depend on pH, hydrolysis and ligands; a bare ionic formula is an analytical shorthand.

The paired cation $\mathrm{H}{\mathrm{g}}_2^{2+}$, containing a mercury–mercury bond and average oxidation state +1.

A chemical compound containing a metal and oxygen; different metal oxidation states can give different oxides.

In migratory insertion, adjacent ligands combine while remaining attached to the metal in the product. In alkene insertion into M–R, R forms a bond to one alkene carbon while the other carbon acquires the M–C bond. metal oxidation state need not change.