Ions, Ionic Compounds, and Covalent Compounds: Nomenclature and Formulas

Ions and Ionic Compounds

Polyatomic Ions

Polyatomic ions are charged species composed of two or more atoms covalently bonded, acting as a single unit in chemical reactions. They are commonly found in many biological and chemical compounds.

• Cation: A positively charged ion (e.g., NH4+, ammonium).

• Anion: A negatively charged ion (e.g., SO42-, sulfate).

• Common Polyatomic Ions:

Name	Formula
Ammonium	NH4+
Hydronium	H3O+
Acetate	C2H3O2-
Chromate	CrO42-
Phosphate	PO43-
Nitrate	NO3-
Sulfate	SO42-
Hydrogen carbonate (bicarbonate)	HCO3-
Hydroxide	OH-
Perchlorate	ClO4-
Permanganate	MnO4-
Additional info: Polyatomic ions are often memorized due to their frequent use in chemical nomenclature.

Nomenclature of Ionic Compounds

Ionic compounds are named by stating the cation first, followed by the anion. The rules for naming depend on whether the ions are monoatomic or polyatomic, and whether the metal can have more than one possible charge.

• Monoatomic cations: Named after the metal (e.g., Na+ is sodium).

• Transition metals: May have multiple charges; the charge is indicated by Roman numerals (e.g., Fe2+ is iron(II)).

• Monoatomic anions: Named by changing the ending of the element to "-ide" (e.g., Cl- is chloride).

• Polyatomic ions: Names are memorized and used as is (e.g., SO42- is sulfate).

Examples: Naming Ionic Compounds

• Co2S3: Cobalt(III) sulfide

• BaCO3: Barium carbonate

• CuCl: Copper(I) chloride

• K3N: Potassium nitride

• CdSO4: Cadmium sulfate

• NH4C2H3O2: Ammonium acetate

• Al2(SO4)3: Aluminum sulfate

• NI3(PO4)2: Nickel(II) phosphate

• Pb(NO3)2: Lead(II) nitrate

• AgNO3: Silver nitrate

Examples: Writing Formulas from Names

• Sodium phosphate: Na3PO4

• Calcium chlorate: Ca(ClO3)2

• Barium oxide: BaO

• Tin(II) nitrate: Sn(NO3)2

• Iron(III) sulfate: Fe2(SO4)3

• Calcium hydroxide: Ca(OH)2

• Silver chlorate: AgClO3

• Aluminum phosphate: AlPO4

• Nickel(II) cyanide: Ni(CN)2

• Lead(II) chromate: PbCrO4

Covalent Compounds

Nomenclature of Covalent Compounds

Covalent compounds are named using prefixes to indicate the number of atoms of each element. The element listed first in the formula is named directly, while the second element's name ends with "-ide". Prefixes are used for both elements except when the first element has only one atom.

Number	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-
7	hepta-
8	octa-
9	nona-
10	deca-

• If the prefix ends in a vowel and the element name begins with a vowel, the prefix vowel is dropped (e.g., monoxide, not monooxide).

Examples: Naming Covalent Compounds

• S2F2: Disulfur difluoride

• IF5: Iodine pentafluoride

• NF3: Nitrogen trifluoride

• P2Cl4: Diphosphorus tetrachloride

• P4S3: Tetraphosphorus trisulfide

• P4S7: Tetraphosphorus heptasulfide

• SeBr4: Selenium tetrabromide

• XeF6: Xenon hexafluoride

• N2F2: Dinitrogen difluoride

• I2O5: Diiodine pentoxide

Examples: Writing Formulas from Names

• Diiodine pentoxide: I2O5

• Dichlorine hexoxide: Cl2O6

• Disulfur difluoride: S2F2

• Xenon trioxide: XeO3

• Tetraphosphorus pentasulfide: P4S5

• Oxygen difluoride: OF2

• Arsenic pentafluoride: AsF5

Comparison Table: Ionic vs. Covalent Compound Nomenclature

Feature	Ionic Compounds	Covalent Compounds
Bond Type	Electrostatic attraction between ions	Shared electrons between atoms
Elements Involved	Metal + Nonmetal (or polyatomic ions)	Nonmetals only
Naming	Cation first, then anion; use Roman numerals for variable charge metals	Prefixes indicate number of atoms; second element ends in "-ide"
Examples	NaCl (sodium chloride), CaCO3 (calcium carbonate)	CO2 (carbon dioxide), N2O5 (dinitrogen pentoxide)

Additional info: Mastery of nomenclature is essential for understanding chemical formulas and reactions, which is foundational for biochemistry and physiology.