Comprehensive Chemical Nomenclature, Formulas, and Molecular Mass Study Guide

Polyatomic Ions and Ionic Nomenclature

  • Polyatomic ions are charged groups of covalently bonded atoms that act as a single ionic unit in chemical compounds.

  • Ionic compounds containing polyatomic ions are named similarly to binary ionic compounds: the cation is named first, followed by the polyatomic anion. The suffix -ide is used only if it is inherently part of the polyatomic ion's name (such as hydroxide or cyanide).

Table 2.6: Some Common Polyatomic Ions

  • Common Polyatomic Cations:

    • Ammonium: NH4+\text{NH}_4^+

    • Hydronium: H3O+\text{H}_3\text{O}^+

  • Common Polyatomic Anions:

    • Acetate: CH3COO−\text{CH}_3\text{COO}^-

    • Carbonate: CO32−\text{CO}_3^{2-}

    • Cyanide: CN−\text{CN}^-

    • Bicarbonate (Hydrogen carbonate): HCO3−\text{HCO}_3^-

    • Hydroxide: OH−\text{OH}^-

    • Chromate: CrO42−\text{CrO}_4^{2-}

    • Hypochlorite: ClO−\text{ClO}^-

    • Dichromate: Cr2O72−\text{Cr}_2\text{O}_7^{2-}

    • Chlorite: ClO2−\text{ClO}_2^-

    • Peroxide: O22−\text{O}_2^{2-}

    • Chlorate: ClO3−\text{ClO}_3^-

    • Phosphate: PO43−\text{PO}_4^{3-}

    • Nitrite: NO2−\text{NO}_2^-

    • Hydrogen phosphate: HPO42−\text{HPO}_4^{2-}

    • Nitrate: NO3−\text{NO}_3^-

    • Sulfite: SO32−\text{SO}_3^{2-}

    • Permanganate: MnO4−\text{MnO}_4^-

    • Sulfate: SO42−\text{SO}_4^{2-}

Examples of Naming Compounds Containing Polyatomic Ions

  • Examples of ionic compounds with polyatomic ions:

    • KNO2\text{KNO}_2 is named potassium nitrite, combining the potassium cation K+\text{K}^+ and the nitrite anion NO2−\text{NO}_2^-.

    • Cr(CO3)3\text{Cr}(\text{CO}_3)_3 is named chromium(III) carbonate, combining the transition metal cation Cr3+\text{Cr}^{3+} and three carbonate anions CO32−\text{CO}_3^{2-}.

    • K2SO4\text{K}_2\text{SO}_4 is named potassium sulfate, consisting of two K+\text{K}^+ cations and one SO42−\text{SO}_4^{2-} polyatomic anion.

    • Fe(ClO4)2\text{Fe}(\text{ClO}_4)_2 is named iron(II) perchlorate, combining one Fe2+\text{Fe}^{2+} cation and two ClO4−\text{ClO}_4^- polyatomic anions.

Naming Oxoanions Pattern Chart

  • Naming Families of Oxoanions:

    • Oxoanions are polyatomic anions containing a central atom bonded to a varying number of oxygen atoms.

    • Prefixes and suffixes are assigned based on the relative number of oxygen atoms attached to the central element root:

    • Highest oxygen count: Prefix per- + element root + Suffix -ate (e.g., ClO4−\text{ClO}_4^- = perchlorate)

    • Standard higher oxygen count: Element root + Suffix -ate (e.g., ClO3−\text{ClO}_3^- = chlorate)

    • Standard lower oxygen count: Element root + Suffix -ite (e.g., ClO2−\text{ClO}_2^- = chlorite)

    • Lowest oxygen count: Prefix hypo- + element root + Suffix -ite (e.g., ClO−\text{ClO}^- = hypochlorite)

Naming Hydrates and Polyatomic Ionic Compounds

  • Hydrates:

    • Hydrates are ionic compounds that have a specific number of water molecules bound within their crystal lattice structure.

    • Hydrates are named by appending the word "hydrate" preceded by a Greek numerical prefix indicating the exact number of water molecules per formula unit (e.g., ⋅8H2O\cdot 8\text{H}_2\text{O} is octahydrate).

Table 2.7: Numerical Prefixes for Hydrates and Binary Covalent Compounds

  • Greek Numerical Prefixes:

    • 1: mono-

    • 2: di-

    • 3: tri-

    • 4: tetra-

    • 5: penta-

    • 6: hexa-

    • 7: hepta-

    • 8: octa-

    • 9: nona-

    • 10: deca-

Perchlorate Ion Structure Comparison

  • Sample Problem 2.10: Determining Names and Formulas of Polyatomic Compounds and Hydrates:

    • Problem (a): Give the systematic name for Fe(ClO4)2\text{Fe}(\text{ClO}_4)_2

    • Solution: The anion ClO4−\text{ClO}_4^- is perchlorate. Since there are two perchlorate ions each carrying a 1−1- charge, iron must possess a 2+2+ charge (Fe2+\text{Fe}^{2+}) to establish charge neutrality. The systematic name is iron(II) perchlorate.

    • Problem (b): Determine the formula for sodium sulfite.

    • Solution: Sodium cation is Na+\text{Na}^+ and sulfite anion is SO32−\text{SO}_3^{2-}. Balancing the charges requires two Na+\text{Na}^+ ions for every one SO32−\text{SO}_3^{2-} anion. The formula is Na2SO3\text{Na}_2\text{SO}_3.

    • Problem (c): Give the systematic name for Ba(OH)2⋅8H2O\text{Ba}(\text{OH})_2 \text{·} 8\text{H}_2\text{O}

    • Solution: Ba2+\text{Ba}^{2+} is barium and OH−\text{OH}^- is hydroxide. The attached 8H2O\text{8H}_2\text{O} is indicated by the prefix octa- followed by hydrate. The full systematic name is barium hydroxide octahydrate.

  • Sample Problem 2.11: Correcting Incorrect Ionic Names and Formulas:

    • Problem (a): Ba(C2H3O2)2\text{Ba}(\text{C}_2\text{H}_3\text{O}_2)_2 is called barium diacetate.

    • Correction: Numerical prefixes such as di- are never used in naming ionic compounds because charge neutrality uniquely determines the stoichiometry. The correct name is barium acetate.

    • Problem (b): Sodium sulfide has the formula Na2(SO3)\text{Na}_2(\text{SO}_3).

    • Correction: Sulfide refers to the monatomic anion S2−\text{S}^{2-}, not the polyatomic oxoanion sulfite (SO32−\text{SO}_3^{2-}). Furthermore, monatomic ions do not use parentheses. The correct formula is Na2S\text{Na}_2\text{S}.

    • Problem (c): Iron(II) sulfate has the formula Fe2(SO4)3\text{Fe}_2(\text{SO}_4)_3

    • Correction: Iron(II) is Fe2+\text{Fe}^{2+} and sulfate is SO42−\text{SO}_4^{2-}. They combine in a 1:1 ratio to form a neutral compound. Fe2(SO4)3\text{Fe}_2(\text{SO}_4)_3 represents iron(III) sulfate. The correct formula is \text{FeSO}_4$.\n - **Problem (d)**: Cesium carbonate has the formula \text{Cs}_2( ext{CO}_3)\n - **Correction**: Parentheses are used around polyatomic ions only when more than one unit of the polyatomic ion is present in the chemical formula. Since only one \text{CO}_3^{2-}groupispresent,parenthesesareomitted.Thecorrectformulaisgroup is present, parentheses are omitted. The correct formula is\text{Cs}_2 ext{CO}_3$.

Naming Binary Acids and Oxoacids

  • Binary Acids:

    • Binary acids form when certain gaseous compounds containing hydrogen and a nonmetal dissolve in water (e.g., gaseous hydrogen chloride, HCl(g)\text{HCl}(g), dissolving in water to yield hydrochloric acid, HCl(aq)\text{HCl}(aq)).

    • Naming structure for binary acids: Prefix hydro- + nonmetal root + Suffix -ic + the word acid.

    • Example: hydro + chlor + ic + acid = hydrochloric acid (HCl\text{HCl}).

Oxoanion Examples: Perbromate and Bromite Ions

  • Oxoacids:

    • Oxoacids are acidic compounds formed by hydrogen combined with an oxoanion.

    • Nomenclature rules based on the parent oxoanion name:

    • Anion suffix -ate changes to -ic in the acid.

    • Anion suffix -ite changes to -ous in the acid.

    • Prefixes per- and hypo- present in the parent oxoanion are fully retained in the acid name.

    • Naming formula: Oxoanion root (+ prefix if applicable) + Suffix -ic or -ous + the word acid.

    • Examples:

    • BrO4−\text{BrO}_4^- is perbromate →\rightarrow HBrO4\text{HBrO}_4 is perbromic acid.

    • BrO2−\text{BrO}_2^- is bromite →\rightarrow HBrO2\text{HBrO}_2 is bromous acid.

  • Sample Problem 2.12: Determining Anion Names and Derived Acid Names/Formulas:

    • Anion (a) Br−\text{Br}^-:

    • Anion Name: Bromide

    • Derived Acid Name: Hydrobromic acid

    • Derived Acid Formula: HBr\text{HBr}

    • Anion (b) IO3−\text{IO}_3^-:

    • Anion Name: Iodate

    • Derived Acid Name: Iodic acid

    • Derived Acid Formula: HIO3\text{HIO}_3

    • Anion (c) CN−\text{CN}^-:

    • Anion Name: Cyanide

    • Derived Acid Name: Hydrocyanic acid

    • Derived Acid Formula: HCN\text{HCN}

    • Anion (d) HSO4−\text{HSO}_4^-:

    • Anion Name: Hydrogen sulfate

    • Derived Acid Name: Sulfuric acid

    • Derived Acid Formula: H2SO4\text{H}_2\text{SO}_4 (Note: the suffix -ic is added to the full element name sulfur, yielding sulfuric, rather than the root sulf-).

Binary Covalent Compounds Nomenclature

  • Binary Covalent Compounds:

    • Formed typically between two nonmetal elements.

    • Element order in formula and name:

    • The element in the lower group number on the periodic table appears first and retains its full element name.

    • If both nonmetals are in the same group, the element with the higher period number (farther down the group) is placed first.

    • The second element is named using its root with the suffix -ide.

    • Greek numerical prefixes indicate the exact number of atoms of each element present in a molecule.

    • The prefix mono- is omitted for the first element in the compound's name.

Figure 2.24: Naming Binary Covalent Compounds Breakdown

  • Sample Problem 2.13: Determining Names and Formulas of Binary Covalent Compounds:

    • Problem (a): What is the formula of carbon disulfide?

    • Solution: Carbon appears first without a prefix (signifying 1 carbon atom). The prefix di- indicates two sulfur atoms. The chemical formula is CS2\text{CS}_2

    • Problem (b): What is the name of PCl5\text{PCl}_5?

    • Solution: P\text{P} is phosphorus. Cl\text{Cl} is chlorine, present as 5 atoms, indicated by penta-. The name is phosphorus pentachloride.

    • Problem (c): Give the name and formula of the compound whose molecules consist of two N\text{N} atoms and four O\text{O} atoms.

    • Solution: Nitrogen has a lower group number than oxygen and is listed first. Two nitrogen atoms require dinitrogen, and four oxygen atoms require tetroxide (or tetraoxide). The formula is N2O4\text{N}_2\text{O}_4 and the systematic name is dinitrogen tetroxide.

  • Sample Problem 2.14: Correcting Incorrect Binary Covalent Names and Formulas:

    • Problem (a): SF4\text{SF}_4 is monosulfur pentafluoride.

    • Correction: Two errors exist: mono- is omitted on the first element, and four fluorine atoms require the prefix tetra-, not penta-. The correct name is sulfur tetrafluoride.

    • Problem (b): Dichlorine heptoxide is Cl2O6\text{Cl}_2\text{O}_6

    • Correction: The prefix hepta- represents seven atoms, whereas six is hexa-. The correct chemical formula is Cl2O7\text{Cl}_2\text{O}_7

    • Problem (c): N2O3\text{N}_2\text{O}_3 is dinitrotrioxide.

    • Correction: The full name of the first element (dinitrogen) must be used, and a space must separate the names of the two elements. The correct name is dinitrogen trioxide.

Straight-Chain Alkanes

  • Hydrocarbons:

    • Organic compounds composed entirely of carbon and hydrogen atoms.

  • Alkanes:

    • The simplest class of hydrocarbons, containing only single covalent bonds.

    • Often called saturated; all single bonds

    • Straight-chain alkanes are named using a root indicating the length of the carbon chain followed by the suffix -ane.

      • general formula for alkanes is C<em>nH</em>2n+2C<em>nH</em>{2n+2}, where nn is the number of carbon atoms in the molecule.

Table 2.8: The First 10 Straight-Chain Alkanes

  • List of the First 10 Straight-Chain Alkanes:

    • 1 Carbon: Methane — Formula: CH4\text{CH}_4

    • 2 Carbons: Ethane — Formula: C2H6\text{C}_2\text{H}_6

    • 3 Carbons: Propane — Formula: C3H8\text{C}_3\text{H}_8

    • 4 Carbons: Butane — Formula: C4H10\text{C}_4\text{H}_{10}

    • 5 Carbons: Pentane — Formula: C5H12\text{C}_5\text{H}_{12}

    • 6 Carbons: Hexane — Formula: C6H14\text{C}_6\text{H}_{14}

    • 7 Carbons: Heptane — Formula: C7H16\text{C}_7\text{H}_{16}

    • 8 Carbons: Octane — Formula: C8H18\text{C}_8\text{H}_{18}

    • 9 Carbons: Nonane — Formula: C9H20\text{C}_9\text{H}_{20}

    • 10 Carbons: Decane — Formula: C10H22\text{C}_{10}\text{H}_{22}

Comprehensive Nomenclature Decision Tree

Figure 2.25: Flowchart for Naming Ionic and Covalent Compounds

  • Step-by-Step Flowchart Procedure for Compound Nomenclature:

    • Question 1: Does the compound contain a metal?

    • If YES (Ionic Compound):

      • Check: Is the metal in Group 1, Group 2, Al\text{Al}, Ag\text{Ag}, Cd\text{Cd}, or Zn\text{Zn} (Fixed Charge Metals)?

      • If YES (Fixed Charge):

        • Contains polyatomic ion?

        • YES: Name cation, then name polyatomic ion (e.g., CaSO4\text{CaSO}_4 = calcium sulfate).

        • NO: Name cation, then name anion with -ide suffix (e.g., CaCl2\text{CaCl}_2 = calcium chloride).

      • If NO (Variable Charge / Transition Metals):

        • Contains polyatomic ion?

        • YES: Name cation with ionic charge as Roman numerals in parentheses (), then name polyatomic ion (e.g., Fe2(SO4)3\text{Fe}_2(\text{SO}_4)_3 = iron(III) sulfate).

        • NO: Name cation with ionic charge as Roman numerals in parentheses (), then name anion with -ide suffix (e.g., FeCl3\text{FeCl}_3 = iron(III) chloride).

    • If NO (Nonmetallic Compound):

      • Check: Is the compound an acid (H\text{H} listed first in formula)?

      • If YES (Acid):

        • Does the acid contain oxygen (oxoacid)?

        • YES: Name polyatomic ion; change -ate to -ic acid or -ite to -ous acid (e.g., HBrO\text{HBrO} = hypobromous acid; HBrO3\text{HBrO}_3 = bromic acid).

        • NO: Binary acid rule: Hydro- + nonmetal root + -ic acid (e.g., HBr\text{HBr} = hydrobromic acid).

      • If NO (Binary Covalent Compound):

        • Name each nonmetal using Greek prefixes to indicate the number of atoms of each element. Add -ide suffix to second element (e.g., N2O5\text{N}_2\text{O}_5 = dinitrogen pentoxide).

Molecular Mass Calculations and Molecular Representations

  • Molecular Mass Definition:

    • The molecular mass of a covalent molecule is the sum of the atomic masses of its constituent atoms:

Molecular Mass=∑Atomic Masses\text{Molecular Mass} = \sum \text{Atomic Masses}

  • Significant Figures Standard:

    • Atomic masses are extracted from the periodic table rounded to four significant figures.

  • Sample Calculation for Water (H2O\text{H}_2\text{O}):

Molecular Mass of H2O=(2×atomic mass of H)+(1×atomic mass of O)\text{Molecular Mass of H}_2\text{O} = (2 \times \text{atomic mass of H}) + (1 \times \text{atomic mass of O})

Molecular Mass of H2O=(2×1.008 amu)+(1×16.00 amu)=18.02 amu\text{Molecular Mass of H}_2\text{O} = (2 \times 1.008\,\text{amu}) + (1 \times 16.00\,\text{amu}) = 18.02\,\text{amu}

  • Formula Mass for Ionic Compounds:

    • Ionic compounds exist as extended crystalline networks rather than discrete molecules. Therefore, their mass is calculated for one formula unit and termed formula mass.

  • Sample Problem 2.15: Calculating Molecular and Formula Mass:

    • Problem (a): Calculate the molecular mass of tetraphosphorus trisulfide.

    • Formula: P4S3\text{P}_4\text{S}_3

    • Calculation:

Molecular Mass=(4×atomic mass of P)+(3×atomic mass of S)\text{Molecular Mass} = (4 \times \text{atomic mass of P}) + (3 \times \text{atomic mass of S})

Molecular Mass=(4×30.97 amu)+(3×32.06 amu)=123.88 amu+96.18 amu=220.06 amu\text{Molecular Mass} = (4 \times 30.97\,\text{amu}) + (3 \times 32.06\,\text{amu}) = 123.88\,\text{amu} + 96.18\,\text{amu} = 220.06\,\text{amu}

  • Problem (b): Calculate the formula mass of ammonium nitrate.

    • Formula: NH4NO3\text{NH}_4\text{NO}_3

    • Calculation:

Formula Mass=(2×atomic mass of N)+(4×atomic mass of H)+(3×atomic mass of O)\text{Formula Mass} = (2 \times \text{atomic mass of N}) + (4 \times \text{atomic mass of H}) + (3 \times \text{atomic mass of O})

Formula Mass=(2×14.01 amu)+(4×1.008 amu)+(3×16.00 amu)=28.02 amu+4.032 amu+48.00 amu=80.05 amu\text{Formula Mass} = (2 \times 14.01\,\text{amu}) + (4 \times 1.008\,\text{amu}) + (3 \times 16.00\,\text{amu}) = 28.02\,\text{amu} + 4.032\,\text{amu} + 48.00\,\text{amu} = 80.05\,\text{amu}

Sample Problem 2.16 Molecular Depictions

  • Sample Problem 2.16: Determining Formula, Name, and Mass from Molecular Depictions:

    • Scene (a): Represents an ionic lattice consisting of purple Na+\text{Na}^+ cations and green F−\text{F}^- anions in a 1:1 array.

    • Chemical Formula: NaF\text{NaF}

    • Compound Name: Sodium fluoride

    • Formula Mass Calculation:

Formula Mass=(1×22.99 amu)+(1×19.00 amu)=41.99 amu\text{Formula Mass} = (1 \times 22.99\,\text{amu}) + (1 \times 19.00\,\text{amu}) = 41.99\,\text{amu}

  • Scene (b): Represents individual gas molecules composed of one blue N\text{N} atom bonded to three green F\text{F} atoms.

    • Chemical Formula: NF3\text{NF}_3

    • Compound Name: Nitrogen trifluoride

    • Molecular Mass Calculation:

Molecular Mass=(1×14.01 amu)+(3×19.00 amu)=14.01 amu+57.00 amu=71.01 amu\text{Molecular Mass} = (1 \times 14.01\,\text{amu}) + (3 \times 19.00\,\text{amu}) = 14.01\,\text{amu} + 57.00\,\text{amu} = 71.01\,\text{amu}

Representing Water with Formulas and Models

  • Representing Molecules with Formulas and Visual Models (Water Example):

    • Molecular Formula: H2O\text{H}_2\text{O} (indicates constituent element types and exact atomic counts).

    • Structural Formulas: Shows connectivity and atomic bonding patterns (e.g., H−O−H\text{H}-\text{O}-\text{H} and Lewis dot structure H:O:H\text{H}:\text{O}:\text{H}).

    • Ball-and-Stick Model: Displays three-dimensional atomic spatial arrangements and explicit bond angles (shows a bond angle of 104.5o104.5^\text{o} for water).

    • Space-Filling Model: Illustrates relative electron cloud sizes and accurate atomic packing radii without explicit bond sticks.