Isoelectronicity

isoelectronicvalence isoelectronicisoelectronic molecules
Isoelectronicity is the phenomenon of two or more chemical species (atoms, molecules, radicals, ions etc.) differing in the atoms of which they are formed but having the same number of valence electrons and the same structure (that is, the same number of atoms with the same connectivity).wikipedia
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Carbon monoxide

COcarbon monoxide (CO)carbon monoxide poisoning
CO,,, and are isoelectronic because each has two nuclei and 10 valence electrons, with each atom considered to have 5 of them (a lone-pair and a triple-bond).
It is the simplest oxocarbon and is isoelectronic with other triply-bonded diatomic molecules having ten valence electrons, including the cyanide anion, the nitrosonium cation and molecular nitrogen.

Azide

azidesazidoN 3 −
CO 2, FCN, N 2 O, NO 2 +, N 3 −, NCO −, and CN 2 2− are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond.
N is a linear anion that is isoelectronic with CO 2, NCO −, N 2 O, NO and NCF.

Hydrogen-like atom

hydrogenichydrogen-likehydrogen atom
Isoelectronicity leads to the concept of hydrogen-like atoms, ions with one electron which are thus isoelectronic with hydrogen.
A hydrogen-like atom/ion (usually called a "hydrogenic atom") is any atomic nucleus bound to one electron and thus is isoelectronic with hydrogen.

Nitronium ion

nitroniumNO 2 + NO
CO 2, FCN, N 2 O, NO 2 +, N 3 −, NCO −, and CN 2 2− are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond.
The nitronium ion is isoelectronic with carbon dioxide and nitrous oxide, and has the same linear structure and bond angle of 180°.

Isolobal principle

isolobalisolobal analogy
* Isolobal principle
Isolobal compounds are analogues to isoelectronic compounds that share the same number of valence electrons and structure.

Diazomethane

methyldiazonium
The uncharged =C=O (ethenone) and -C≡N (cyanamide) molecules and the zwitterionic == (diazomethane) molecule are isoelectronic.

Chemical species

specieschemical componentaqueous species
Isoelectronicity is the phenomenon of two or more chemical species (atoms, molecules, radicals, ions etc.) differing in the atoms of which they are formed but having the same number of valence electrons and the same structure (that is, the same number of atoms with the same connectivity).

Atom

atomsatomic structureatomic
Isoelectronicity is the phenomenon of two or more chemical species (atoms, molecules, radicals, ions etc.) differing in the atoms of which they are formed but having the same number of valence electrons and the same structure (that is, the same number of atoms with the same connectivity).

Molecule

molecularmoleculesmolecular structure
The uncharged =C=O (ethenone) and -C≡N (cyanamide) molecules and the zwitterionic == (diazomethane) molecule are isoelectronic. Isoelectronicity is the phenomenon of two or more chemical species (atoms, molecules, radicals, ions etc.) differing in the atoms of which they are formed but having the same number of valence electrons and the same structure (that is, the same number of atoms with the same connectivity).

Radical (chemistry)

free radicalradicalfree radicals
Isoelectronicity is the phenomenon of two or more chemical species (atoms, molecules, radicals, ions etc.) differing in the atoms of which they are formed but having the same number of valence electrons and the same structure (that is, the same number of atoms with the same connectivity).

Valence electron

valencevalence orbitaloutermost electron
Isoelectronicity is the phenomenon of two or more chemical species (atoms, molecules, radicals, ions etc.) differing in the atoms of which they are formed but having the same number of valence electrons and the same structure (that is, the same number of atoms with the same connectivity).

Electron configuration

electronic configurationconfigurationelectronic structure
At one extreme these require identity of the total electron count and with it the entire electron configuration.

Structural formula

condensed structural formulachemical structurestructural formulae
(Slight differences of, for example, structural formula, such as a double versus single bond, commonly have major effects.)

Monatomic gas

monatomicMonoatomicmonoatomic gas
In such monatomic cases, there is a clear trend in the sizes of such species, with atomic radius decreasing as charge increases.

Atomic radius

atomic radiiatomicatomic size
In such monatomic cases, there is a clear trend in the sizes of such species, with atomic radius decreasing as charge increases.

Ion

cationanionions
Isoelectronicity is the phenomenon of two or more chemical species (atoms, molecules, radicals, ions etc.) differing in the atoms of which they are formed but having the same number of valence electrons and the same structure (that is, the same number of atoms with the same connectivity). In such monatomic cases, there is a clear trend in the sizes of such species, with atomic radius decreasing as charge increases.

Formal charge

formal chargesformalvalence charge
Isoelectronicity does not relate to formal charge on the atoms in a structure: these all have the same configuration even though carbon monoxide has formal charges that are balanced ( − :C≡O: + ) whereas dinitrogen has each atom neutral (:N≡N:) and nitrosonium has an overall net charge.

Carbon dioxide

CO 2 CO2carbon dioxide (CO 2 )
CO 2, FCN, N 2 O, NO 2 +, N 3 −, NCO −, and CN 2 2− are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond.

Cyanogen fluoride

FCNNCF
CO 2, FCN, N 2 O, NO 2 +, N 3 −, NCO −, and CN 2 2− are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond.

Nitrous oxide

laughing gasN 2 Onitrous
CO 2, FCN, N 2 O, NO 2 +, N 3 −, NCO −, and CN 2 2− are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond.

Cyanate

NCO − cyanate anioncyanate ion
CO 2, FCN, N 2 O, NO 2 +, N 3 −, NCO −, and CN 2 2− are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond.

Cyanamide

Hydrogen cyanamideCN 2 2− cyanoimino
CO 2, FCN, N 2 O, NO 2 +, N 3 −, NCO −, and CN 2 2− are all isoelectronic, and each has multiple resonance forms: one with two double bonds and 2 lone pairs on each of the outer atoms, and one with one single bond and one triple bond. The uncharged =C=O (ethenone) and -C≡N (cyanamide) molecules and the zwitterionic == (diazomethane) molecule are isoelectronic.

Hydrogen

HH 2 hydrogen gas
Isoelectronicity leads to the concept of hydrogen-like atoms, ions with one electron which are thus isoelectronic with hydrogen.

Ethenone

keteneetheneketene (ethenone)
The uncharged =C=O (ethenone) and -C≡N (cyanamide) molecules and the zwitterionic == (diazomethane) molecule are isoelectronic.

Zwitterion

zwitterionicZwitterionsinner salt
The uncharged =C=O (ethenone) and -C≡N (cyanamide) molecules and the zwitterionic == (diazomethane) molecule are isoelectronic.