Chemical Naming and Formulas Notes

Names and Formulas of Compounds

  • Superscripts and Subscripts

    • Superscripts (above) indicate the charge of an ion.
    • Example: Na$^+$, S$^{-2}$
    • Subscripts (below) indicate the count of atoms in a chemical formula.
    • Example: H$2$O, NH$3$
    • A chemical formula indicates the number of atoms in the smallest representative unit.
      • Formula unit = ionic, molecule = covalent.

  • Writing Ionic Compounds

    • Ionic compounds are electrically neutral; total charge must add up to zero.
    • Total positive charge must equal total negative charge.
    • Ionic formulas have cation listed first, then anion.

  • Common Ion Names

    • Monatomic anions:
    • Iodine → Iodide
    • Bromine → Bromide
    • Special names for some elements (e.g., oxygen → oxide, sulfur → sulfide).

  • Naming Ionic Compounds

    • Example: MgO, AlCl$3$, Zn$3$P$2$, Li$2$S, NaBr, BeF$_2$.

Transition Metals and Roman Numerals

  • Examples of Transition Metal Names
    • Name for Cr$^{3+}$: Chromium (III)
    • Name for Zn$^{2+}$: Zinc (II)
  • Roman Numerals
    • Roman numerals indicate the charge of the cation, not the number of atoms.

Polyatomic Ions

  • Common Polyatomic Ions
    • Charge = -1:
    • C$2$H$3$O$_2^{-}$ → acetate
    • NO$_2^{-}$ → nitrite
    • Charge = -2:
    • SO$_3^{-2}$ → sulfite
    • CO$_3^{-2}$ → carbonate
  • Using Parentheses
    • Parentheses ( ) used when multiple polyatomic ions are present in a formula.
    • Example: Ca(NO$3$)$2$ uses parentheses, whereas Li$2$CO$3$ does not.

Covalent (Molecular) Compounds

  • Characteristics
    • Formed between nonmetals.
    • Presence of metals or polyatomic ions indicates ionic compounds instead.
  • Prefixes Indicating Number of Atoms
    • The prefix in covalent compounds specifies the number of each atom.

Naming Acids and Bases

  • Identifying Acids

    • Chemical formulas typically start with H.
    • Example: HCl (hydrochloric acid) has a different naming structure based on endings of anions.

  • Naming Rules for Acids
    a) -ide to hydro-…ic acid (e.g., HCl = hydrochloric acid).
    b) -ite to …ous acid (e.g., HNO$2$ = nitrous acid). c) -ate to …ic acid (e.g., HNO$3$ = nitric acid).

  • Common Acids

    • Examples of common acids include: HCl, HNO$3$, H$2$S, H$2$SO$4$.

  • Bases

    • Formulas ending in OH$^-$ are bases, named according to the ionic name (e.g., NaOH = sodium hydroxide).

Common Naming and Formula Errors

  • Common mistakes include incorrect naming and formula representation.
  • Review and correct the names and formulas of common compounds.
    • Example:
      a) Incorrect: dinickel trioxide
      b) Correct: Ni$2$O$3$ (Nickel (III) oxide)
  • Understand why certain names or formulas are incorrect and how to correct them.

This study guide provides an in-depth understanding of chemical naming conventions, particularly for ionic and covalent compounds, as well as acids and bases, which is essential for mastering concepts in chemistry.