Study Notes on Chemical Formulas and Nomenclature

2.2 Writing Chemical Formulas and Naming Compounds

• Chemical formulas:

  • Describe the elements in a compound and the quantity of each element present.

  • Nomenclature system for naming substances is largely governed by the IUPAC system (International Union of Pure and Applied Chemists).

  • Additionally, reference will be made to older systems, but IUPAC is the preferred method.

Part 1: Naming Elements

• Naming Origins:

  • Elements are named after individuals (e.g., Curium for Marie Curie), places (e.g., Europium), or deities (e.g., Plutonium).

  • Some names have ancient origins (e.g., Gold).

• Element Symbols:

  • Typically derived from the first letter or first two letters of the element name, with the second letter in lowercase.

  • Certain symbols reflect Latin names, such as Fe for iron (from ferrum).

  • The periodic table provides a comprehensive list of elements and their respective symbols.

• Oxidation State (Valence Number):

  • Defined as the number of electrons an atom can gain, lose, or share during chemical bonding.

  • Electropositive Elements:

  • Tend to lose electrons, forming positive ions (cations), denoted by a + sign.

  • Electronegative Elements:

  • Tend to gain electrons, resulting in negative ions (anions), denoted by a - sign.

  • Some elements possess multiple oxidation states; the last bolded oxidation state is used for non-metals from the periodic table.

  • For metals with multiple oxidation states, the valence number is indicated in the name utilizing Roman numerals.

Part 2: Naming Compounds

• Binary Compounds:

  • Defined as the simplest forms of compounds composed of two elements.

  • Types of Compounds:

  • Ionic Compounds: Formed when a metallic element combines with a non-metallic element.

  • Molecular (Covalent) Compounds: Formed when two non-metals bond.

• Ionic Compounds (Metal + Non-Metal):

  • Steps for Naming Ionic Compounds:

  1. Name the first element (metal cation).

  2. Name the second element (non-metal anion), changing its ending to ‘IDE.’

  3. Identify the valence number for metals with multiple valences using Roman numerals.

  4. To identify the valence of the metal, check the non-metal's valence number multiplied by the number of non-metal atoms to balance the charge.

  5. Display brackets and Roman numerals only if necessary after the metal's name.

• Memorize these Roman Numerals:

  • I - One, II - Two, III - Three, IV - Four, V - Five, VI - Six, VII - Seven, VIII - Eight, IX - Nine, X - Ten.

• Examples of Ionic Compounds:

  • KCl: potassium chloride

  • MgF₂: magnesium fluoride

  • Na₃P: sodium phosphide

  • CuO: copper (II) oxide

  • Cu₂O: copper (I) oxide

  • SnS₂: tin (IV) sulfide

• Steps for Writing Chemical Formulas for Ionic Compounds:

  1. Write symbols for the elements involved.

  2. Determine valence numbers, remembering to use Roman numerals for metals with multiple valences.

  3. Apply the crossover method for valence numbers as subscripts to determine the quantity of atoms in the compound.

  4. Reduce subscripts to their lowest terms when applicable.

• Naming Binary Compounds Containing Two Non-Metals (Covalent):

  • Steps:

  1. Element order based on B, Si, C, Sb, As, P, N, H, Te, Se, S, At, I, Br, Cl, O, F.

  2. Use prefixes to indicate the number of atoms for each element.

     • Prefixes:

       • mono = 1

       • di = 2

       • tri = 3

       • tetra = 4

       • penta = 5

       • hexa = 6

       • hepta = 7

       • octa = 8

       • nona = 9

       • deca = 10

  3. Name elements with their corresponding prefixes; adjust the second element's name to end in ‘IDE’.

  • Examples of Covalent Compounds:

  • NO: nitrogen monoxide

  • NO₂: nitrogen dioxide

  • PCl₃: phosphorus trichloride

  • H₂O₂: dihydrogen dioxide

Part III: Bases and Acids

• Properties of Bases:

  • Formed when metal oxides dissolve in water.

  • Indicators of bases include:

  • Litmus paper turns blue.

  • pH is greater than 7.

  • Sour taste and slippery texture.

  • Conducts electricity and is corrosive.

  • Phenolphthalein turns pink in basic conditions.

  • Common household cleaners contain basic substances, such as ammonia.

  • Hydroxyl Ion: Bases include hydroxide ions

• Naming Bases:

  1. Name the metal ion first.

  2. If multiple valence numbers are present, indicate the applicable one with Roman numerals in brackets.

  3. Add hydroxide to the name.

• Examples of Bases:

  • Al(OH)₃: aluminum hydroxide

  • Sr(OH)₂: strontium hydroxide

  • LiOH: lithium hydroxide

  • Fe(OH)₃: iron (III) hydroxide

Writing Formulas for Bases

• Steps for Writing Formulas of Bases:

  1. Write the metal's symbol.

  2. Include OH for the hydroxide ion.

  3. Apply the metal's valence number (if it's indicated) to determine the subscript for the hydroxide group.

  4. Put brackets around the hydroxide if its subscript exceeds one.

Part IV: Binary and Ternary Acids

• Binary Acids:

  • Formed from a non-metallic oxide or an ionic compound with hydrogen dissolved in water.

  • Two types:

  • Inorganic (mineral) acids: Found mainly in non-living entities.

  • Organic acids: Found in living organisms.

• Properties of Acids:

  • Litmus turns red.

  • Taste sour.

  • Conducts electricity and are corrosive.

  • pH is less than 7.

  • In acidic solutions, phenolphthalein appears clear.

• Naming Binary Acids:

  1. Start the name with ‘hydro’ to signify it is a binary acid.

  2. Rename the non-metal by changing its ending to ‘ic.’

  3. Conclude with the word ‘acid.’

• Examples of Binary Acids:

  • HCl(aq): hydrochloric acid

  • H₂S(aq): hydrosulfuric acid

Writing Formulas for Binary Acids

• Steps for Writing Formulas of Binary Acids:

  1. Write H for hydrogen.

  2. Incorporate the non-metal's symbol.

  3. Cross over the valence numbers to determine the subscripts.

  4. Schedule (aq) after the name to indicate it's aqueous.

Ternary Acids

• Definition: Compounds containing hydrogen, non-metal, and oxygen. Each ternary acid has a family of four derivatives differing by the number of oxygen atoms.

• Parent Acids: Memorization of the following eight acids is required:

  • H₃PO₄: phosphoric acid

  • H₂SO₄: sulfuric acid

  • HClO₃: chloric acid
    (and others as listed)

• Naming Patterns for Ternary Acids:

  • Derived from a parent acid, modification in naming corresponds to the number of oxygen atoms present:

  • example: HClO₄ is perchloric acid; HClO is hypochlorous acid depending on the number of oxygen atoms.

Polyatomic Ions

• Resulting from dissociation of ternary acids into ions, these ions may react with metals, producing a new naming system based on the oxygens present.

• Examples:

  • Perchlorate: ClO₄^(-1) derived from perchloric acid (HClO₄).

  • Chlorate: ClO₃^(-1) from chloric acid (HClO₃).

Naming Polyatomic Compounds

1. Name the metal.

2. If applicable, denote valence with Roman numerals in brackets based on the charge of the polyatomic ion.

3. Name the polyatomic ion according to its relation to the parent acid (ate or ite).

• Examples for Polyatomic Compounds:

  • Na₂SO₄: sodium sulfate

  • Ca(NO₂)₂: calcium nitrite

  • Sn(BrO₄)₄: tin (IV) perbromate

• Complete the polyatomic compounds worksheet.

• Memorize the following:

  • Parent acids:

  • H₃PO₄: phosphoric acid

  • H₂SO₄: sulfuric acid

  • HClO₃: chloric acid

  • (and others as listed).

  • Naming patterns for acids and ions.

  • For binary acids, start the name with ‘hydro’ and change the non-metal's ending to ‘ic’; conclude with the word ‘acid’.

  • For bases, name the metal first and add hydroxide.

  • Review the steps for writing formulas for acids and bases:

  • For binary acids: Write H for hydrogen, include the non-metal's symbol, and cross over valence numbers.

  • For bases: Write the metal's symbol, include OH for hydroxide, and apply the metal's valence number to determine the subscript for hydroxide.