Comprehensive Guide to Chemical Cations and Anions

Periodic Group Charge Trends

Alkali metals consistently lose a single valence electron to form stable cations with an ionic charge of $+1$ .
Alkaline earth metals lose two valence electrons to attain a stable octet, forming cations with an ionic charge of $+2$ .
Halogens gain a single electron to fill their outermost valence shell, consistently forming halide anions with an ionic charge of $-1$ .

Monatomic Cations of Fixed and Variable Oxidation States

Monovalent and fixed-charge metals:
- Silver forms a monovalent cation with the formula $\text{Ag}^{+1}$ .
- Zinc forms a divalent transition metal cation with the formula $\text{Zn}^{+2}$ .
- Aluminum forms a trivalent main-group metal cation with the formula $\text{Al}^{+3}$ .
Multivalent transition metals and post-transition metals governed by Stock nomenclature:
- Copper forms two common oxidation states:
- Copper I possesses an oxidation state of $+1$ and is written as $\text{Cu}^{+1}$ .
- Copper II possesses an oxidation state of $+2$ and is written as $\text{Cu}^{+2}$ .
- Iron forms two distinct cationic states:
- Iron II possesses an oxidation state of $+2$ and is written as $\text{Fe}^{+2}$ .
- Iron III possesses an oxidation state of $+3$ and is written as $\text{Fe}^{+3}$ .
- Lead forms two post-transition cationic states:
- Lead II possesses an oxidation state of $+2$ and is written as $\text{Pb}^{+2}$ .
- Lead IV possesses an oxidation state of $+4$ and is written as $\text{Pb}^{+4}$ .
- Tin exhibits two oxidation states:
- Tin II possesses an oxidation state of $+2$ and is written as $\text{Sn}^{+2}$ .
- Tin IV possesses an oxidation state of $+4$ and is written as $\text{Sn}^{+4}$ .
- Chromium exhibits multiple cationic forms:
- Chromium II possesses an oxidation state of $+2$ and is written as $\text{Cr}^{+2}$ .
- Chromium III possesses an oxidation state of $+3$ and is written as $\text{Cr}^{+3}$ .
- Manganese exhibits multivalent character:
- Manganese II possesses an oxidation state of $+2$ and is written as $\text{Mn}^{+2}$ .
- Manganese III possesses an oxidation state of $+3$ and is written as $\text{Mn}^{+3}$ .
- Cobalt forms two primary cations:
- Cobalt II possesses an oxidation state of $+2$ and is written as $\text{Co}^{+2}$ .
- Cobalt III possesses an oxidation state of $+3$ and is written as $\text{Co}^{+3}$ .
- Nickel primarily forms:
- Nickel II possesses an oxidation state of $+2$ and is written as $\text{Ni}^{+2}$ .
- Gold exhibits two distinct oxidation states:
- Gold I possesses an oxidation state of $+1$ and is written as $\text{Au}^{+1}$ .
- Gold III possesses an oxidation state of $+3$ and is written as $\text{Au}^{+3}$ .

Polyatomic and Dimeric Cations

Mercury presents two unique cationic species:
- Mercury I is a diatomic or dimeric cation consisting of two mercury atoms covalently bonded together carrying a net charge of $+2$ , written with the formula $\text{Hg}_2^{+2}$ .
- Mercury II is a monatomic divalent cation carrying a charge of $+2$ , written with the formula $\text{Hg}^{+2}$ .
Ammonium is a common nitrogen-based polyatomic cation carrying a net positive charge of $+1$ , written with the formula $\text{NH}_4^{+1}$ .

Monatomic Anions

Halogen anions (halides) carry a characteristic charge of $-1$ .
Oxide is a divalent anion formed by oxygen gaining two electrons, yielding the formula $\text{O}^{-2}$ .
Sulfide is a divalent anion formed by sulfur gaining two electrons, yielding the formula $\text{S}^{-2}$ .
Nitride is a trivalent anion formed by nitrogen gaining three electrons, yielding the formula $\text{N}^{-3}$ .
Phosphide is a trivalent anion formed by phosphorus gaining three electrons, yielding the formula $\text{P}^{-3}$ .
Arsenide is a trivalent anion formed by arsenic gaining three electrons, yielding the formula $\text{As}^{-3}$ .

Polyatomic Oxyanions and Hydrogen-Bearing Oxyanions

Phosphorus oxyanion family:
- Phosphate is the fully oxidized phosphorus oxyanion with the formula $\text{PO}_4^{-3}$ .
- Phosphite possesses one fewer oxygen atom than phosphate while maintaining a charge of $-3$ , resulting in the formula $\text{PO}_3^{-3}$ .
- Hydrogen phosphate is formed by adding one hydrogen ion ( $\text{H}^{+1}$ ) to phosphate, which reduces the negative charge by one unit, yielding the formula $\text{HPO}_4^{-2}$ .
- Dihydrogen phosphate is formed by adding two hydrogen ions to phosphate, reducing the negative charge by two units, yielding the formula $\text{H}_2\text{PO}_4^{-1}$ .
Sulfur oxyanion family:
- Sulfate is the tetraoxygen sulfur anion carrying a charge of $-2$ , with the formula $\text{SO}_4^{-2}$ .
- Sulfite contains one fewer oxygen atom than sulfate and carries a charge of $-2$ , with the formula $\text{SO}_3^{-2}$ .
- Hydrogen sulfate (also called bisulfate) incorporates one hydrogen ion, reducing the overall charge to $-1$ , with the formula $\text{HSO}_4^{-1}$ .
- Hydrogen sulfite (also called bisulfite) incorporates one hydrogen ion with sulfite, reducing the overall charge to $-1$ , with the formula $\text{HSO}_3^{-1}$ .
Carbon oxyanion family:
- Carbonate is a planar divalent oxyanion carrying a charge of $-2$ , with the formula $\text{CO}_3^{-2}$ .
- Hydrogen carbonate (also known as bicarbonate) incorporates a single proton into the carbonate structure, resulting in a charge of $-1$ and the formula $\text{HCO}_3^{-1}$ .
Nitrogen oxyanion family:
- Nitrate is the higher oxidation state oxyanion of nitrogen with three oxygen atoms and a charge of $-1$ , with the formula $\text{NO}_3^{-1}$ .
- Nitrite contains one fewer oxygen atom than nitrate while retaining the $-1$ charge, with the formula $\text{NO}_2^{-1}$ .
Chlorine oxyanion family (characterized by varying oxygen oxidation levels with a uniform $-1$ charge):
- Perchlorate possesses the maximum oxidation state of chlorine with four oxygens, formula $\text{ClO}_4^{-1}$ .
- Chlorate possesses three oxygens, formula $\text{ClO}_3^{-1}$ .
- Chlorite possesses two oxygens, formula $\text{ClO}_2^{-1}$ .
- Hypochlorite possesses a single oxygen, formula $\text{ClO}^{-1}$ .
Transition metal oxyanions:
- Chromate is a mononuclear oxyanion of chromium with a charge of $-2$ , formula $\text{CrO}_4^{-2}$ .
- Dichromate is a dinuclear oxyanion containing two chromium atoms and seven oxygen atoms with a charge of $-2$ , formula $\text{Cr}_2\text{O}_7^{-2}$ .
- Permanganate is an oxyanion containing manganese in a high oxidation state with four oxygen atoms and a charge of $-1$ , formula $\text{MnO}_4^{-1}$ .

Organic, Diatomic, and Pseudohalide Anions

Acetate is a polyatomic organic carboxylate anion with a net charge of $-1$ , with the formula $\text{C}_2\text{H}_3\text{O}_2^{-1}$ .
Oxalate is a dicarboxylate anion containing two carbon and four oxygen atoms with a net charge of $-2$ , with the formula $\text{C}_2\text{O}_4^{-2}$ .
Cyanide is a diatomic pseudohalide anion consisting of carbon and nitrogen triple-bonded together with a net charge of $-1$ , with the formula $\text{CN}^{-1}$ .
Hydroxide is a fundamental diatomic polyatomic anion composed of one oxygen atom and one hydrogen atom with a net charge of $-1$ , with the formula $\text{OH}^{-1}$ .
Peroxide is a diatomic oxygen anion containing an oxygen-oxygen covalent bond where the pair carries a net charge of $-2$ , with the formula $\text{O}_2^{-2}$ .