Naming Elements, Ions, and Compounds

Introduction

This study guide covers the foundational principles for naming chemical elements, ions, and compounds, as encountered in a General Chemistry college course. Understanding these naming conventions is essential for communicating chemical information accurately and for success in laboratory and theoretical chemistry.

Elements

Monoatomic and Molecular Elements

Elements can exist as single atoms (monoatomic) or as molecules composed of two or more atoms of the same element.

• Monoatomic Elements: Elements that exist as single atoms, such as Cu (copper) and Hg (mercury).

• Molecular Elements: Elements that exist as molecules, typically diatomic or polyatomic, such as H2, N2, O2, F2, Cl2, Br2, I2.

• Common Polyatomic Elements: S8 (sulfur), P4 (phosphorus), P10, Cdiamond, Cgraphite.

Allotropes

Some elements exist in different structural forms called allotropes. For example, phosphorus has white, red, and violet allotropes, and carbon exists as diamond and graphite.

Naming Elements

• Elements are named simply by their element name (e.g., hydrogen).

• Extra language may be used for context:

  • Atom: H

  • Molecule: H2

  • Gas: H2(g)

Ions

Monoatomic Ions

Ions are atoms or groups of atoms with a net electric charge due to loss or gain of electrons.

• Cations: Positively charged ions, usually metals. Named as the element followed by the word "ion" (e.g., Na+ is sodium ion).

• Anions: Negatively charged ions, usually nonmetals. Named by taking the root of the element name and adding the suffix "-ide" (e.g., N3- is nitride ion).

• Transition Metal Ions: May have multiple charges, indicated by Roman numerals (e.g., Fe2+ is iron(II) ion, Fe3+ is iron(III) ion).

Polyatomic Ions

Polyatomic ions are groups of atoms covalently bonded that carry a net charge.

• Examples:

  • NO3- (nitrate ion)

  • SO42- (sulfate ion)

  • NH4+ (ammonium ion)

• Oxoanions: Polyatomic ions containing oxygen. Naming depends on the number of oxygens and the central atom.

  • SO42- is sulfate

  • SO32- is sulfite

Compounds

Molecular Compounds

Molecular compounds are formed from nonmetals. Their names reflect the number and type of atoms present.

• Use prefixes to indicate the number of each atom:

  • 1: mono-

  • 2: di-

  • 3: tri-

  • 4: tetra-

  • 5: penta-

  • 6: hexa-

  • 7: hepta-

  • 8: octa-

  • 9: nona-

  • 10: deca-

• The first element keeps its name; the second element's name ends in "-ide".

• Example: CO is carbon monoxide, N2O is dinitrogen monoxide.

Ionic Compounds

Ionic compounds are formed from cations (usually metals) and anions (usually nonmetals or polyatomic ions). The formula is written to balance the charges.

• Name the cation first, then the anion.

• Do not indicate the number of ions; the charges determine the ratio.

• Example: NaCl is sodium chloride, Mg3N2 is magnesium nitride.

Table: Common Monoatomic and Polyatomic Ions

Hydrated Ionic Compounds

Some ionic compounds contain water molecules in their structure, called hydrates.

• Example: CuSO4·5H2O is copper(II) sulfate pentahydrate.

Acids

Binary Acids

Binary acids consist of hydrogen and one other nonmetal element. They release hydrogen ions when dissolved in water.

• Name with the prefix "hydro-" and the suffix "-ic" followed by "acid".

• Example: HCl(aq) is hydrochloric acid, HBr(aq) is hydrobromic acid.

Oxoacids

Oxoacids contain hydrogen, oxygen, and another element. The name is based on the polyatomic ion present.

• If the ion ends in "-ate", the acid name ends in "-ic" (e.g., H2SO4 is sulfuric acid).

• If the ion ends in "-ite", the acid name ends in "-ous" (e.g., H2SO3 is sulfurous acid).

Calculating Molar Mass

Definition and Application

The molar mass of a compound is the sum of the atomic masses of all atoms in its formula.

• Formula:

• Example: For NaCl:

Periodic Table Classification

Metals, Nonmetals, and Metalloids

The periodic table classifies elements as metals, nonmetals, or metalloids, which helps predict their chemical behavior and the types of compounds they form.

• Metals: Typically form cations and ionic compounds.

• Nonmetals: Typically form anions and molecular compounds.

• Metalloids: Exhibit properties of both metals and nonmetals.

Summary Table: Prefixes for Molecular Compounds

Additional info: Some context and examples have been expanded for clarity and completeness, including the explanation of allotropes, hydrated compounds, and the use of prefixes in molecular compound naming.