Common Polyatomic Ions

Introduction to Polyatomic Ions

  • Definition of Polyatomic Ions: A polyatomic ion is a charged chemical species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered to be acting as a single unit. These ions possess a net charge because the total number of electrons is not equal to the total number of protons in the group of atoms.

  • Naming Conventions (The Oxyanion Series):

    • Suffixes: The suffix "-ate" is used for the common oxyanion of an element. The suffix "-ite" is used for an oxyanion with one less oxygen atom than the "-ate" form.

    • Prefixes: The prefix "per-" indicates one more oxygen atom than the "-ate" ion. The prefix "hypo-" indicates one less oxygen atom than the "-ite" ion.

    • Hydrogen Prefixes: The addition of the word "hydrogen" (or the prefix "bi-") indicates the addition of a hydrogen ion (H+H^+) to the parent anion. This addition reduces the negative charge magnitude of the parent ion by exactly one.

Carbon-Based Polyatomic Anions

  • Acetate

    • Chemical Formulas: C2H3O2−C_2H_3O_2^- or CH3COO−CH_3COO^-

    • Transcript Notation: Captured as CHO and CH3COO.

    • Note: It is the conjugate base of acetic acid (CH3COOHCH_3COOH).

  • Carbonate

    • Chemical Formula: CO32−CO_3^{2-}

    • Transcript Notation: Recorded as co,.

    • Charge: −2-2 valence state.

  • Hydrogen carbonate (or bicarbonate)

    • Chemical Formula: HCO3−HCO_3^-

    • Transcript Notation: Recorded as HCO,.

    • Relationship: This ion is the conjugate base of carbonic acid (H2CO3H_2CO_3) and the conjugate acid of the carbonate ion (CO32−CO_3^{2-}).

The Halogen Oxyanion Series (Chlorine-Oxygen Ions)

  • Hypochlorite

    • Chemical Formula: ClO−ClO^-

    • Transcript Notation: Recorded as CIO.

    • Description: The lowest oxygen state in the chlorine oxyanion series.

  • Chlorite

    • Chemical Formula: ClO2−ClO_2^-

    • Transcript Notation: Recorded as CIO.

    • Description: Contains one more oxygen atom than hypochlorite.

  • Chlorate

    • Chemical Formula: ClO3−ClO_3^-

    • Transcript Notation: Associated with the entry following Chlorite.

    • Description: The standard oxygen state for chlorine oxyanions.

  • Perchlorate

    • Chemical Formula: ClO4−ClO_4^-

    • Transcript Notation: Recorded as CIO.

    • Description: The highest oxygen state in the chlorine oxyanion series.

Nitrogen and Cyanide Based Ions

  • Nitrate

    • Chemical Formula: NO3−NO_3^-

    • Transcript Notation: Recorded as NO,.

    • Note: The more common oxyanion of nitrogen.

  • Nitrite

    • Chemical Formula: NO2−NO_2^-

    • Transcript Notation: Recorded as NO.

    • Note: Contains one less oxygen than nitrate.

  • Cyanide

    • Chemical Formula: CN−CN^-

    • Note: A diatomic anion consisting of a carbon atom and a nitrogen atom triple-bonded together.

Sulfur-Based Polyatomic Anions

  • Sulfate

    • Chemical Formula: SO42−SO_4^{2-}

    • Transcript Notation: Recorded as SO.

    • Note: Common divalent oxyanion of sulfur.

  • Sulfite

    • Chemical Formula: SO32−SO_3^{2-}

    • Transcript Notation: Recorded as So,.

    • Note: Contains one less oxygen than sulfate.

  • Hydrogen sulfate (or bisulfate)

    • Chemical Formula: HSO4−HSO_4^-

    • Transcript Notation: Recorded as HSO.

    • Note: Formed by adding a proton (H+H^+) to sulfate.

  • Hydrogen sulfite (or bisulfite)

    • Chemical Formula: HSO3−HSO_3^-

    • Transcript Notation: Recorded as HSO.

    • Note: Formed by adding a proton (H+H^+) to sulfite.

Phosphorus-Based Polyatomic Anions

  • Phosphate

    • Chemical Formula: PO43−PO_4^{3-}

    • Transcript Notation: Recorded as PO3-.

    • Charge: Maintains a trivalent negative charge (−3-3).

  • Hydrogen phosphate

    • Chemical Formula: HPO42−HPO_4^{2-}

    • Transcript Notation: Recorded as HPO.

    • Charge: Divalent negative charge (−2-2).

  • Dihydrogen phosphate

    • Chemical Formula: H2PO4−H_2PO_4^-

    • Transcript Notation: Recorded as H.PO.

    • Charge: Monovalent negative charge (−1-1).

Metal-Based Polyatomic Anions

  • Chromate

    • Chemical Formula: CrO42−CrO_4^{2-}

    • Transcript Notation: Recorded as Cro.

  • Dichromate

    • Chemical Formula: Cr2O72−Cr_2O_7^{2-}

    • Transcript Notation: Recorded as ar,0₁.

    • Structure: Contains two chromium atoms and seven oxygen atoms.

  • Permanganate

    • Chemical Formula: MnO4−MnO_4^-

    • Transcript Notation: Recorded as MnO.

    • Note: A powerful oxidizing agent containing manganese in its highest oxidation state.

Basic and Diatomic Oxy-Anions

  • Hydroxide

    • Chemical Formula: OH−OH^-

    • Note: The distinctive ion of bases.

  • Peroxide

    • Chemical Formula: O22−O_2^{2-}

    • Transcript Notation: Recorded as O.

    • Note: Contains an Oxygen-Oxygen single bond.

Polyatomic Cations

  • Ammonium

    • Chemical Formula: NH4+NH_4^+

    • Transcript Notation: Recorded as NH,.

    • Note: One of the few common polyatomic cations; it is formed by the protonation of ammonia (NH3NH_3).