Ionic Compounds, Nomenclature, and Polyatomic Ions

Vocabulary flashcards covering the octet rule, ionic compound formation, criss-cross formula writing, and polyatomic ion nomenclature (including oxyanions, prefixes, and suffixes).

Octet Rule

The rule stating that atoms gain, lose, or share electrons so as to acquire the stable electron structure of a nearby noble gas.

Ionic Bond

A chemical bond formed when metals combine with non-metals; the metal loses one or more electrons and the non-metal gains one or more electrons, commonly forming a cubic crystalline lattice.

Formula Unit

The fundamental unit of an ionic compound representing the lowest whole-number ratio of ions.

Criss-Cross Method

A method to write ionic formulas where the numerical charge of each ion crosses over to become the subscript of the opposite ion, which is then reduced to the lowest whole-number ratio if needed.

Iron(III) Oxide

An ionic compound composed of $Fe^{3+}$ and $O^{2-}$; balancing charges requires two iron ions ($+6$ total) and three oxide ions ($-6$ total) to equal zero, giving the formula $Fe_2O_3$.

Fixed-Charge Metal Cations ($Ag^+$, $Zn^{2+}$, $Cd^{2+}$)

Specific metal ions whose predictable charges must be memorized: silver carries a $+1$ charge ($Ag^+$), while zinc ($Zn^{2+}$) and cadmium ($Cd^{2+}$) both carry a $+2$ charge.

Monatomic Ion

An ion consisting of a single atom carrying an electrical charge (e.g., $Co^{2+}$ or $Cl^-$).

Polyatomic Ion

An ion composed of an assembly of two or more covalently bonded atoms that carries an overall net electrical charge.

Oxyanions

Polyatomic anions containing oxygen bonded to another element, which follow systematic naming rules with specific prefixes and suffixes based on the number of oxygen atoms.

-ate (Suffix)

The standard suffix used for the base form of an oxyanion (e.g., chlorate, nitrate, sulfate, phosphate).

-ite (Suffix)

A suffix denoting an oxyanion that has one fewer oxygen atom than the corresponding base "-ate" ion, while retaining the same overall ionic charge.

Hypo- (Prefix)

A prefix meaning "under" or "less," used in conjunction with the suffix "-ite" for an oxyanion with one fewer oxygen atom than the "-ite" form (e.g., hypochlorite, $ClO^-$).

Per- (Prefix)

A prefix meaning "super" or "hyper," used in conjunction with the suffix "-ate" for an oxyanion with one more oxygen atom than the base "-ate" form (e.g., perchlorate, $ClO_4^-$).

Hypochlorite

An oxyanion with the chemical formula $ClO^-$, which serves as the main active ingredient in household bleach ($NaOCl$).

Chlorite

An oxyanion of chlorine with the chemical formula $ClO_2^-$.

Chlorate

The base form oxyanion of chlorine with the chemical formula $ClO_3^-$.

Perchlorate

An oxyanion of chlorine containing four oxygen atoms, with the chemical formula $ClO_4^-$.

Nitrate Ion

The base form oxyanion of nitrogen with the chemical formula $NO_3^-$.

Nitrite Ion

An oxyanion of nitrogen containing one less oxygen atom than nitrate, with the chemical formula $NO_2^-$.

Sulfate Ion

The base form oxyanion of sulfur with the chemical formula $SO_4^{2-}$.

Sulfite Ion

An oxyanion of sulfur with one less oxygen atom than sulfate, having the chemical formula $SO_3^{2-}$.

Phosphate Ion

The base form oxyanion of phosphorus with the chemical formula $PO_4^{3-}$.

Carbonate Ion

A polyatomic oxyanion with the chemical formula $CO_3^{2-}$.

Acetate Ion

A polyatomic ion with the chemical formula $C_2H_3O_2^-$, often recommended and written as $CH_3COO^-$.

Oxalate Ion

A polyatomic anion with the chemical formula $C_2O_4^{2-}$.

Permanganate Ion

A polyatomic oxyanion with the chemical formula $MnO_4^-$.

Hydroxide Ion

A polyatomic anion with the formula $OH^-$, formed in the equilibrium dissociation of liquid water: $HOH(l) \rightleftharpoons H^+(aq) + OH^-(aq)$.

Cyanide Ion

A polyatomic anion without oxygen having the chemical formula $CN^-$.

Ammonium Ion

A positively charged polyatomic ion without oxygen having the chemical formula $NH_4^+$.

Hydronium Ion

A positively charged polyatomic ion with the chemical formula $H_3O^+$.

Ammonium Phosphate

An ionic compound composed of the polyatomic ions $NH_4^+$ and $PO_4^{3-}$, yielding the formula $(NH_4)_3PO_4$.

Sodium Nitrate

An ionic compound composed of the sodium cation ($Na^+$) and the nitrate polyatomic anion ($NO_3^-$), having the formula $NaNO_3$.