Comprehensive Guide to Naming Ions, Ionic Compounds, Acids, and Covalent Molecules

Fundamentals of Ionic Compounds and Electron Transfer

• Formula Types: Formulas for ionic compounds are generally written as empirical formulas, representing the simplest whole-number ratio of ions.

• Electronic Neutrality: Every ionic compound must be electronically neutral. This means the total positive charge from the cations must exactly equal the total negative charge from the anions.

• Electron Transfer Process (Sodium Chloride Example):     - Sodium atom ($Na$): Contains $11$ protons ($11p$) and $11$ electrons ($11e$). It loses one electron to become a Sodium ion ($Na^+$) consisting of $11p$ and $10e$.     - Chlorine atom ($Cl$): Contains $17$ protons ($17p$) and $17$ electrons ($17e$). It gains one electron to become a Chloride ion ($Cl^-$) consisting of $17p$ and $18e$.     - Result: The transfer of an electron from sodium to chlorine results in the formation of a sodium chloride crystal ($NaCl$), which is an ionic solid.

Determining Formulas for Ionic Compounds

• Neutrality Calculation: To achieve a neutral formula, the sum of charges must equal zero: $\text{Sum of charges} = 0$.

• Examples of Charge Balancing:     - Aluminum Oxide ($Al_2O_3$): Consists of aluminum cations ($Al^{3+}$) and oxide anions ($O^{2-}$). To balance: $2 \times (+3) + 3 \times (-2) = 6 - 6 = 0$.     - Calcium Bromide ($CaBr_2$): Consists of calcium cations ($Ca^{2+}$) and bromide anions ($Br^-$). To balance: $1 \times (+2) + 2 \times (-1) = 2 - 2 = 0$.     - Sodium Carbonate ($Na_2CO_3$): Consists of sodium cations ($Na^+$) and carbonate anions ($CO_3^{2-}$). To balance: $2 \times (+1) + 1 \times (-2) = 2 - 2 = 0$.

Classification and Naming of Ionic Compounds

• Identification: A compound is most likely ionic if it contains a metal and a nonmetal.

• Naming Fixed-Charge Metal Cations:     - Applies to Alkali metals (Group 1A), Alkaline earth metals (Group 2A), and specific ions: $Ag^+$, $Al^{3+}$, $Cd^{2+}$, and $Zn^{2+}$.     - Rule: Name the metal first, followed by the root of the nonmetal name with the suffix -ide.

• Naming Variable-Charge Metal Cations:     - Applies to transition metals and other metals that can form multiple ions.     - Rule: Name the metal first, specify the specific charge of the metal cation using a Roman numeral in parentheses, and add the -ide suffix to the nonmetal root.

Common Monatomic Ions

Cations (Positive Ions)

• $+1$ Charge:     - Hydrogen ($H^+$)     - Lithium ($Li^+$)     - Sodium ($Na^+$)     - Potassium ($K^+$)     - Silver ($Ag^+$)     - Cesium ($Cs^+$)     - Copper(I) or Cuprous ($Cu^+$)

• $+2$ Charge:     - Magnesium ($Mg^{2+}$)     - Calcium ($Ca^{2+}$)     - Strontium ($Sr^{2+}$)     - Barium ($Ba^{2+}$)     - Zinc ($Zn^{2+}$)     - Cadmium ($Cd^{2+}$)     - Cobalt(II) or Cobaltous ($Co^{2+}$)     - Copper(II) or Cupric ($Cu^{2+}$)     - Iron(II) or Ferrous ($Fe^{2+}$)     - Lead(II) or Plumbous ($Pb^{2+}$)     - Manganese(II) ($Mn^{2+}$)     - Mercury(II) or Mercuric ($Hg^{2+}$)     - Tin(II) or Stannous ($Sn^{2+}$)     - Chromium(II) or Chromous ($Cr^{2+}$)

• $+3$ Charge:     - Aluminum ($Al^{3+}$)     - Chromium(III) or Chromic ($Cr^{3+}$)     - Iron(III) or Ferric ($Fe^{3+}$)     - Cobalt(III) or Cobaltic ($Co^{3+}$)

• $+4$ Charge:     - Lead(IV) ($Pb^{4+}$)     - Tin(IV) ($Sn^{4+}$)

• Special Cation: Mercury(I) or Mercurous is a diatomic ion represented as $Hg_2^{2+}$.

Anions (Negative Ions)

• $-1$ Charge:     - Hydride ($H^-$)     - Fluoride ($F^-$)     - Chloride ($Cl^-$)     - Bromide ($Br^-$)     - Iodide ($I^-$)

• $-2$ Charge:     - Oxide ($O^{2-}$)     - Sulfide ($S^{2-}$)

• $-3$ Charge:     - Nitride ($N^{3-}$)

Molecules and Covalent Bonds

• Molecule: The basic unit of a molecular element or covalent compound. It consists of two or more atoms bonded by the sharing of electrons. Most covalent substances are molecular.

• Covalent Bond Formation:     - Far Apart: No interactions between atoms.     - Closing Distance: Attraction forces (between the nucleus of one atom and the electron of another) increase. Repulsions (between nuclei and between electrons) remain weak.     - Optimum Distance: The molecule forms when attraction forces balance repulsion forces perfectly.

• Elements Occurring as Molecules:     - Diatomic molecules: $H_2$, $N_2$, $O_2$, $F_2$, $Cl_2$, $Br_2$, $I_2$.     - Tetratomic molecules: Phosphorus ($P_4$).     - Octatomic molecules: Sulfur ($S_8$) and Selenium ($Se_8$).

• Polyatomic Ion: A group of two or more atoms covalently bonded together that possesses an overall electrical charge (e.g., the carbonate ion in calcium carbonate). In many reactions, these ions remain together as a single unit.

Chemical Formulas and Nomenclature Rules

• Chemical Formula: Consists of element symbols with numerical subscripts indicating the type and number of each atom in the smallest unit of the substance.

• Binary Ionic Compounds:     - Listing Order: Cation is always listed first, followed by the anion.     - Cation Name: Identical to the metal name (often ending in "-ium").     - Anion Name: Derived from the nonmetal root + suffix -ide.     - Example: Calcium and Bromine form Calcium Bromide ($CaBr_2$).

Sample Problems: Binary Ionic Compounds

Naming Compounds from Elements

• Magnesium and Nitrogen: Aluminum is the metal, Nitrogen the nonmetal. Result: Magnesium nitride.

• Iodine and Cadmium: Cadmium is the metal, Iodine the nonmetal. Result: Cadmium iodide.

• Strontium and Fluorine: Strontium is the metal, Fluorine the nonmetal. Result: Strontium fluoride.

• Sulfur and Cesium: Cesium is the metal, Sulfur the nonmetal. Result: Cesium sulfide.

Determining Empirical Formulas

• Magnesium nitride: Ions are $Mg^{2+}$ and $N^{3-}$. Lowest common multiple of charges is $6$. Needs $3 \times Mg^{2+}$ and $2 \times N^{3-}$. Formula: $Mg_3N_2$.

• Cadmium iodide: Ions are $Cd^{2+}$ and $I^-$. Needs $1 \times Cd^{2+}$ and $2 \times I^-$. Formula: $CdI_2$.

• Strontium fluoride: Ions are $Sr^{2+}$ and $F^-$. Needs $1 \times Sr^{2+}$ and $2 \times F^-$. Formula: $SrF_2$.

• Cesium sulfide: Ions are $Cs^+$ and $S^{2-}$. Needs $2 \times Cs^+$ and $1 \times S^{2-}$. Formula: $Cs_2S$.

Naming with Variable Charges

• $SnF_2$: Tin is $Sn^{2+}$, Fluorine is $F^-$. Systematic Name: Tin(II) fluoride.

• $CrI_3$: Iodine is $I^-$. Three $I^-$ means Chromium must be $+3$. Systematic Name: Chromium(III) iodide.

• Ferric oxide: "Ferric" denotes $Fe^{3+}$, Oxide is $O^{2-}$. Formula: $Fe_2O_3$.

• $CoS$: Sulfide is $S^{2-}$, so Cobalt must be $Co^{2+}$. Systematic Name: Cobalt(II) sulfide.

Polyatomic Ions and Oxoanions

List of Common Polyatomic Ions

• Cations:     - Ammonium: $NH_4^+$     - Hydronium: $H_3O^+$

• Anions:     - Acetate: $CH_3COO^-$     - Cyanide: $CN^-$     - Hydroxide: $OH^-$     - Hypochlorite: $ClO^-$     - Chlorite: $ClO_2^-$     - Chlorate: $ClO_3^-$     - Perchlorate: $ClO_4^-$     - Nitrite: $NO_2^-$     - Nitrate: $NO_3^-$     - Permanganate: $MnO_4^-$     - Carbonate: $CO_3^{2-}$     - Bicarbonate (Hydrogen carbonate): $HCO_3^-$     - Chromate: $CrO_4^{2-}$     - Dichromate: $Cr_2O_7^{2-}$     - Peroxide: $O_2^{2-}$     - Phosphate: $PO_4^{3-}$     - Hydrogen phosphate: $HPO_4^{2-}$     - Sulfite: $SO_3^{2-}$     - Sulfate: $SO_4^{2-}$

Naming Oxoanions based on Oxygen Count

• Highest oxygen count: Prefix per- + root + suffix -ate.

• High oxygen count: Root + suffix -ate.

• Lower oxygen count: Root + suffix -ite.

• Lowest oxygen count: Prefix hypo- + root + suffix -ite.

Numerical Prefixes for Hydrates and Covalent Compounds

• $1$: mono-

• $2$: di-

• $3$: tri-

• $4$: tetra-

• $5$: penta-

• $6$: hexa-

• $7$: hepta-

• $8$: octa-

• $9$: nona-

• $10$: deca-

Complex Ionic Compound Problems

Case Studies

• $Fe(ClO_4)_2$: $ClO_4^-$ is perchlorate. Iron balances two perchlorates, so it is $Fe^{2+}$. Name: Iron(II) perchlorate.

• Sodium sulfite: Sodium is $Na^+$, sulfite is $SO_3^{2-}$. Formula: $Na_2SO_3$.

• $Ba(OH)_2 \times 8H_2O$: Barium hydroxide combined with $8$ water units. Name: Barium hydroxide octahydrate.

Correcting Common Errors

• Error: $Ba(C_2H_3O_2)_2$ called "barium diacetate."     - Correction: Prefixes like "di-" are not used for ionic compounds. Correct name: Barium acetate.

• Error: Sodium sulfide formula $(Na)_2SO_3$.     - Correction: Monatomic ions do not need parentheses. Sulfide is $S^{2-}$, while $SO_3^{2-}$ is sulfite. Correct formula: $Na_2S$.

• Error: Iron(II) sulfate formula $Fe_2(SO_4)_3$.     - Correction: Iron(II) is $Fe^{2+}$ and Sulfate is $SO_4^{2-}$. Only one of each is needed for neutrality. Correct formula: $FeSO_4$.

• Error: Cesium carbonate formula $Cs_2(CO_3)$.     - Correction: Parentheses are only needed if there is more than one polyatomic ion unit. Correct formula: $Cs_2CO_3$.

Naming Acids

Binary Acids

• Formed when certain gaseous compounds (like $HCl$) dissolve in water.

• Rule: Prefix hydro- + nonmetal root + suffix -ic + the word acid.

• Example: $HCl(aq)$ is hydrochloric acid.

Oxoacids

• Derived from oxoanions.

• Rule: If the anion ends in -ate, the acid ends in -ic.

• Rule: If the anion ends in -ite, the acid ends in -ous.

• Retention: Prefixes hypo- and per- are kept from the anion name.

• Examples:     - Anion: Bromide ($Br^-$) $\rightarrow$ Acid: Hydrobromic acid ($HBr$).     - Anion: Iodate ($IO_3^-$) $\rightarrow$ Acid: Iodic acid ($HIO_3$).     - Anion: Cyanide ($CN^-$) $\rightarrow$ Acid: Hydrocyanic acid ($HCN$).     - Anion: Hydrogen sulfate ($HSO_4^-$) $\rightarrow$ Acid: Sulfuric acid ($H_2SO_4$).

Binary Covalent Compounds

• Formation: Formed by combinations of two nonmetals.

• Rules for Order: The element with the lower group number in the periodic table is listed first in the name and formula. Its name remains unchanged.

• Rules for Suffix: The second element is named using its root plus the suffix -ide.

• Rules for Quantities: Numerical prefixes specify the exact number of atoms of each element.

• Examples:     - Carbon disulfide: Formula: $CS_2$.     - $PCl_5$: Name: Phosphorus pentachloride.     - $N_2O_4$: Name: Dinitrogen tetroxide.

Correcting Covalent Names/Formulas

• Error: $SF_4$ called "monosulfur pentafluoride."     - Correction: "Mono-" is not used for the first element. "Penta-" means five, but the subscript is four (tetra). Correct name: Sulfur tetrafluoride.

• Error: Dichlorine heptoxide formula $Cl_2O_6$.     - Correction: "Hepta-" means seven, not six. Correct formula: $Cl_2O_7$.

• Error: $N_2O_3$ called "dinitrotrioxide."     - Correction: The suffix "-ide" must be attached to the root of the second element. Correct name: Dinitrogen trioxide.