8.27 Acid Naming, Polyatomic Ions, and Ionic/Naming Rules (Review Flashcards)

Acid Naming and Formula Practice (Transcript-Derived Notes)

General goal: distinguish ionic vs covalent naming systems and know when to use binary vs oxyacid naming rules.

Binary acids

Definition: acids formed from hydrogen and one other nonmetal (no metals involved).
Naming rule: use the prefix hydro-, then the root of the nonmetal name, followed by the suffix -ic and the word acid.
- Example:
- Hydrochloric acid from the formula $ext{HCl}$ (hydro + chlor + -ic + acid).
- Hydrosulfuric acid from the formula $ext{H}_2 ext{S}$ (historical common name; still considered binary with H and S).
Important implication from the transcript: binary acids begin with hydro and include exactly hydrogen + one other element in the formula.
Practice example discussed: hydrochloric acid vs sulfide-based naming; when sulfur is the nonmetal, the derived acid name is sulfuric (for sulfate) or sulfurous (for sulfite) in the oxyacid family, not a binary hydro name.
Formula-building reminder: to write the formula for hydrosulfuric acid, you consider H and S and the neutral/charge balance concept used for ionic-like representations in this teaching approach (see “crisscross” for polyatomic ions and balancing rules below).
Quick recap formula examples:
- $ext{H}_2 ext{S} ightarrow ext{hydrosulfuric acid}$
- $ext{HCl} ightarrow ext{hydroclor ic acid}$ (standard correctly written as hydrochloric acid in many texts; the hydro- form is used in strict binary naming).

Oxyacids

Definition: acids that include a polyatomic anion with oxygen (usually ends in -ate or -ite in the base anion name).
Key rule: oxyacids do not start with hydro-.
Naming from polyatomic roots:
- -ate in the polyatomic anion becomes -ic in the acid name.
- -ite in the polyatomic anion becomes -ous in the acid name.
- Examples:
- Sulfate (
  $ext{SO}_4^{2-}$ ) → sulfuric acid (H₂SO₄)
- Sulfite (
  $ext{SO}_3^{2-}$ ) → sulfurous acid (H₂SO₃)
- Nitrate (
  $ext{NO}_3^{-}$ ) → nitric acid (HNO₃)
- Nitrite (
  $ext{NO}_2^{-}$ ) → nitrous acid (HNO₂)
Memorization guidance from transcript:
- Memorize polyatomic ions that end in -ate vs -ite (e.g., sulfate vs sulfite) to derive the acid names quickly.
- Some students memorize a few key patterns or use memory tricks (e.g., “ap es” mnemonic or memorizing the set of common polyatomic ions).
Example from the transcript:
- Carbonate (
  $ext{CO}_3^{2-}$ ) → carbonic acid (H₂CO₃)
- Bicarbonate (
  $ext{HCO}_3^{-}$ ) is a special named form; when used as bicarbonate in formulas, remember its charge and balance accordingly.
Polyatomic-ion-driven approach: identify the polyatomic ion in the acid, then apply the appropriate -ate → -ic or -ite → -ous transformation.

Key polyatomic ions (memory aids discussed in transcript)

Carbonate: $ext{CO}_3^{2-}$
Bicarbonate: $ext{HCO}_3^{-}$
Nitrate: $ext{NO}_3^{-}$
Nitrite: $ext{NO}_2^{-}$
Sulfate: $ext{SO}_4^{2-}$
Sulfite: $ext{SO}_3^{2-}$
Chlorate: $ext{ClO}_3^{-}$
Chlorite: $ext{ClO}_2^{-}$
Hypochlorite: $ext{ClO}^{-}$
Perchlorate: $ext{ClO}_4^{-}$
Acetate: $ext{C}2 ext{H}3 ext{O}_2^{-}$
Cyanide: $ext{CN}^{-}$ (polyatomic anion)
Cyanate: $ext{OCN}^{-}$ (polyatomic anion)

How to decide binary vs oxyacids quickly

If the name or formula contains a hydrogen and a nonmetal with no oxygen in the anion part, think binary hydroacid.
If the compound includes a polyatomic anion that contains oxygen (ending in -ate or -ite), think oxyacid and apply the -ate → -ic/-ite → -ous transformation.
Chloride/hypochlorite examples discuss how prefixes and oxidation state context can influence naming choices in practice (e.g., hypochlorite is a polyatomic oxoanion, not a simple binary chloride).

Naming and writing formula practice (from transcript)

When given a formula, determine if it is binary or involves polyatomic ions, then apply the appropriate naming rules.
Example: H₂SO₄ is sulfuric acid (from sulfate, ending -ate → -ic).
Example: H₂SO₃ is sulfurous acid (from sulfite, ending -ite → -ous).
Example: HClO₂ would be chlorous acid (from chlorite, -ite → -ous; note: this is an oxyacid derived from a chlorite ion).
Example: HNO₃ is nitric acid (from nitrate, -ate → -ic).
Example: HCN is related to cyanide; cyanide is a polyatomic anion. The transcript notes that cyanide is polyatomic and can lead to a related acid name; e.g., hydrocyanic acid can be used for HCN in some naming conventions.

Writing formulas from names (criss-cross method, with polyatomic ions)

Steps:
- Write the cation and the anion from the name.
- Use oxidation states to balance charges, crossing charges to become subscripts.
- When a polyatomic ion is involved and appears more than once, enclose it in parentheses.
- Reduce to the lowest whole-number ratio.
Example from transcript:
- Titanium(IV) nitrate →
- Titanium is Ti⁴⁺; nitrate is NO₃⁻.
- Formula: $ext{Ti(NO}3)4$ (criss-cross: 4 NO₃⁻ balance the +4 Ti⁴⁺)
Example: Manganese(II) cyanide → Mn(CN)₂
- Mn²⁺ with CN⁻; formula: $ext{Mn(CN)}_2$
Example: Lead(IV) oxide → PbO₂
- Pb⁴⁺ with O²⁻; charge balance leads to PbO₂
Example: Platinum(IV) carbonate → Pt(CO₃)₂
- Carbonate is CO₃²⁻; if you have Pt⁴⁺, you'd balance with two carbonate ions → Pt(CO₃)₄? (note: transcript mentions carbonate-based balancing; the general criss-cross concept is what matters here)
Example: Silver sulfite → Ag₂SO₃
- Ag⁺ with SO₃²⁻; formula crosses to balance charges; silver typically +1; 2 Ag⁺ balance one SO₃²⁻ → Ag₂SO₃
Example: Calcium phosphate → Ca₃(PO₄)₂
- Phosphate is PO₄³⁻; calcium is Ca²⁺; balancing yields Ca₃(PO₄)₂
Example: Calcium bicarbonate → Ca(HCO₃)₂
- Bicarbonate is HCO₃⁻; calcium is Ca²⁺; balance yields Ca(HCO₃)₂
Example: Bicarbonate vs bisulfate naming memory aid:
- Bisulfate: HSO₄⁻; Bicarbonate: HCO₃⁻; these reflect hydrogen paired with the polyatomic anion and a change in charge.

Covalent (molecular) naming and prefixes (practice notes)

For molecular compounds (covalent), use prefixes to denote the number of atoms of each element:
- mono-, di-, tri-, tetra-, penta-, hexa-, etc.
- Do not always use the prefix for the first element (often omitted when there is only one atom of the first element).
Examples from practice discourse:
- CO → carbon monoxide (not carbon mono oxide in common practice; note the standard is carbon monoxide).
- CO₂ → carbon dioxide.
- N₂H₄ → diazane? (in practice this would be:N₂H₄ is diazane or hydrazine; transcript’s example lists NH₃ as nitrogen trihydride, i.e., ammonia, to illustrate covalent naming).
- NH₃ → nitrogen trihydride (common name: ammonia).
- P₂O₅ → diphosphorus pentoxide.
- SiS₄ → silicon tetrasulfide.
- Si₃Cl₈ → trisilicon octachloride (transcript’s phrasing: “trisilicon octane chloride,” mapping to the idea of a tri-silicon compound with chlorides).
- OBr₂ → oxygen dibromide.
The transcript emphasizes that many covalent names can be trickier and that memorization of polyatomic ions remains crucial for acid naming as well as for ionic naming.

Group trends and naming conventions (notes from the discussion)

Roman numerals in ionic nomenclature:
- Use Roman numerals to indicate the oxidation state of metals with variable charges.
- Do not use Roman numerals for certain metals with fixed charges.
Metals with fixed charges (as per the transcript):
- Group 1 metals (alkali metals) – fixed +1 charge.
- Group 2 metals (alkaline earth metals) – fixed +2 charge.
- Aluminum (Al) – fixed +3 charge when forming compounds.
- Scandium (Sc), Zinc (Zn), and Silver (Ag) – often do not require Roman numerals in many common formulas due to their typical fixed oxidation states in compounds.
When a metal does have a variable charge, determine its charge by balancing with the anion side and then write the roman numeral accordingly (e.g., Cr in Cr₂O₇²⁻ is determined by balancing with the dichromate anion, CrO₄²⁻, etc.).
Important tip from the transcript: don’t rely on rote memorization alone; practice both directions: naming compounds from formulas and writing formulas from names, especially with polyatomic ions and transition metals.

Worked examples (recap of several items mentioned in the transcript)

Ammonium nitrate: $ext{NH}4 ext{NO}3$
- Ammonium ion NH₄⁺; nitrate NO₃⁻; overall neutral compound.
Copper(I) acetate (as discussed): formula could be written as $ext{CuC}2 ext{H}3 ext{O}_2$ (copper in +1 oxidation state, acetate is C₂H₃O₂⁻).
Silver sulfite: $ext{Ag}2 ext{SO}3$ (Ag⁺ with SO₃²⁻).
Lead(IV) oxide: $ext{PbO}_2$ (Pb⁴⁺ with O²⁻).
Calcium phosphate: $ext{Ca}3( ext{PO}4)_2$ (Ca²⁺ with PO₄³⁻).
Titanium(IV) nitrate: $ext{Ti}( ext{NO}3)4$
Manganese(II) cyanide: $ext{Mn}( ext{CN})_2$
Dichromate vs Chromate notes from the transcript:
- Dichromate ion: $ext{Cr}2 ext{O}7^{^{2-}}$ (as discussed; common name dichromate).
Hypochlorite and related oxyanions:
- Hypochlorite: $ext{ClO}^-$ ; from which other halogen oxyanions like chlorite, chlorate, perchlorate can be derived in the context of oxyacid naming.
Diphosphorus pentoxide: $ext{P}2 ext{O}5$ .
Trisilicon octachloride: $ext{Si}3 ext{Cl}8$ (as discussed in the covalent naming section).
Xenon fluorides (from the recitation activity examples): e.g., XeFₙ (as discussed in the transcript; e.g., XeF₄ or XeF₆ were part of the group exercise; transcript specifically mentions XeF9).
Silicon tetrasulfide: $ext{SiS}_4$ .
Oxygen dihalide/labeled dihydride examples: $ext{OBr}_2$ .
Carbon dioxide: $ext{CO}_2$ .
Ammonium vs hydrogen-bicarbonate memory devices: $ext{NH}4^+, ext{ HCO}3^-$ (context for balancing and naming).

Practical implications and study tips

Acid naming hinges on recognizing whether the compound is binary or oxyacid; this determines whether you use the hydro-prefix or the polyatomic-based naming; practice both directions (name→formula and formula→name).
For oxyacids, memorize the common polyatomic ions and their charges; this enables you to convert between the -ate/-ite polyatomic base and the corresponding -ic/-ous acid.
For binary acids, remember the hydro prefix and that the nonmetal partner’s name is altered to end with -ic before adding acid.
In building formulas from names, always write the cation first then the anion, cross-charge to balance, and use parentheses around polyatomic ions when more than one is present.
When using Roman numerals, only include them for metals with variable oxidation states; many main-group metals (Group 1, Group 2, Al, Zn, Ag, Sc in common practice) do not require Roman numerals.
Expect mixes of naming systems on exams; stay comfortable with badges like:
- Binary acids: hydro- + nonmetal root + -ic + acid (e.g., HCl → hydrochloric acid).
- Oxyacids: polyatomic root + -ate/-ite → -ic/-ous + acid (e.g., SO₄²⁻ → sulfuric acid).
- Ionic nomenclature: cation name (and charge if needed) + anion name; use parentheses for polyatomic ions when necessary.
Time-management tip from the session: practice both types of problems in a mixed set, since tests often present non-segmented, jumbled problems.

Quick reference formulas and names (compact cheat sheet)

Binary acids (example forms):
- $ext{HCl} ightarrow ext{hydrochloric acid}$
- $ext{H}_2 ext{S} ightarrow ext{hydrosulfuric acid}$
Oxyacids (from -ate/-ite):
- $ext{NO}_3^{-} ightarrow ext{nitric acid}$
- $ext{NO}_2^{-} ightarrow ext{nitrous acid}$
- $ext{SO}_4^{2-} ightarrow ext{sulfuric acid}$
- $ext{SO}_3^{2-} ightarrow ext{sulfurous acid}$
Notable polyatomic ions:
- Carbonate: $ext{CO}3^{2-}$ ; Bicarbonate: $ext{HCO}3^{-}$
- Nitrate: $ext{NO}3^{-}$ ; Nitrite: $ext{NO}2^{-}$
- Chlorate: $ext{ClO}3^{-}$ ; Chlorite: $ext{ClO}2^{-}$ ; Hypochlorite: $ext{ClO}^{-}$ ; Perchlorate: $ext{ClO}_4^{-}$
- Acetate: $ext{C}2 ext{H}3 ext{O}_2^{-}$ ; Cyanide: $ext{CN}^{-}$ ; Cyanate: $ext{OCN}^{-}$
Examples to memorize for practice:
- $ext{Ca}( ext{HCO}3)2$ (calcium bicarbonate)
- $ext{Ca}3( ext{PO}4)_2$ (calcium phosphate)
- $ext{Ti}( ext{NO}3)4$ (titanium(IV) nitrate)
- $ext{Mn(CN)}_2$ (manganese(II) cyanide)
- $ext{PbO}_2$ (lead(IV) oxide)
- $ext{Ag}2 ext{SO}3$ (silver sulfite)
- $ext{CuC}2 ext{H}3 ext{O}_2$ (copper(I) acetate)
- $ext{NO}_? ext{ etc.}$ (practice varies; refer to the transcript’s list for additional item types)
Note: Some items in the transcript reflect student-group practice items (e.g., XeF₉, Si₃Cl₈, OBr₂, etc.). Treat these as examples of covalent/molecular naming and memorize the appropriate formulas and names as exercise items.

Summary takeaway

Acid naming integrates two primary systems (binary hydroacids and oxyacids from polyatomic ions).
Mastery hinges on recognizing the underlying ion types, memorizing key polyatomic ions, and knowing when to use Roman numerals for metal ions with variable charges.
Practice both directions: naming compounds from formulas and writing formulas from names, using parentheses for polyatomic ions as needed and reducing to the simplest whole-number ratio.
Expect mixed problems on exams; the ability to switch between naming conventions quickly is essential.