Classification and Chemical Properties of Inorganic Substances

Classification of Inorganic Substances

• Definition of Classification: The systematic division of all known inorganic substances into distinct groups or classes of compounds based on shared characteristics.

• Criteria for Classification: Inorganic substances are primarily classified based on:

  • Qualitative and quantitative composition

  • Chemical structure

  • Chemical properties

• Major Categories of Chemical Substances:

  • Simple Substances: Formed by atoms of a single chemical element.

  • Metals

  • Nonmetals

  • Complex Substances: Formed by atoms of two or more different chemical elements. These are divided into major chemical classes:

  • Oxides

  • Acids

  • Bases

  • Salts

Oxides: Definition, Oxidation States, and Nomenclature

• Definition: Oxides are complex binary substances consisting of atoms of two chemical elements, one of which is oxygen.

• Oxidation State of Oxygen: In all oxides, the oxidation state of the oxygen atom is equal to $-2$

• Examples of Oxides across Different Oxidation States:

  • Potassium oxide: $\overset{+1}{K}_2\overset{-2}{O}$

  • Barium oxide: $\overset{+2}{Ba}\overset{-2}{O}$

  • Aluminum oxide: $\overset{+3}{Al}_2\overset{-2}{O}_3$

  • Carbon(IV) oxide: $\overset{+4}{C}\overset{-2}{O}_2$

  • Phosphorus(V) oxide: $\overset{+5}{P}_2\overset{-2}{O}_5$

  • Sulfur(VI) oxide: $\overset{+6}{S}\overset{-2}{O}_3$

  • Chlorine(VII) oxide: $\overset{+7}{Cl}_2\overset{-2}{O}_7$

  • Osmium(VIII) oxide: $\overset{+8}{Os}\overset{-2}{O}_4$

• Nomenclature Rules for Oxides:

  • The standard name of an oxide consists of the word "oxide" followed by the name of the second element.

  • Examples with fixed oxidation states:

    • $H_2O$ — hydrogen oxide

    • $CaO$ — calcium oxide

  • If an element can exist in multiple oxidation states and form several oxides, its specific oxidation state in that compound is indicated by a Roman numeral in parentheses immediately following the element name:

  • Carbon(II) oxide: $\overset{+2}{C}\overset{-2}{O}$

  • Carbon(IV) oxide: $\overset{+4}{C}\overset{-2}{O}_2$

Classification and Chemical Properties of Oxides

• General Categorization by Reactivity: Based on their ability to react with acids and bases (alkalis) to form salts, oxides are divided into:

  • Non-salt-forming oxides: Oxides that do not form salts when interacting with acids or bases.

  • Salt-forming oxides: Oxides that react to form salts.

• Subdivisions of Salt-Forming Oxides:

  • Basic oxides

  • Acidic oxides

  • Amphoteric oxides

  • Fundamental Distinction: The key difference among these three classes lies in their distinct chemical behavior toward acids and alkalis.

• Chemical Properties of Basic Oxides:

  • Interaction with Acids:

  • Products: Salt and water

  • Chemical equation: $CaO + 2HCl \rightarrow CaCl_2 + H_2O$

  • Interaction with Acidic Oxides:

  • Products: Salt

  • Chemical equation: $Na_2O + CO_2 \rightarrow Na_2CO_3$

  • Interaction with Water:

  • Condition: Only oxides of alkali metals and alkaline earth metals react with water.

  • Products: Soluble bases (alkalis)

  • Chemical equation: $CaO + H_2O \rightarrow Ca(OH)_2$

• Chemical Properties of Acidic Oxides:

  • Interaction with Alkalis (Soluble Bases):

  • Products: Salt and water

  • Chemical equation: $CO_2 + 2NaOH \rightarrow Na_2CO_3 + H_2O$

  • Interaction with Basic Oxides:

  • Products: Salt

  • Chemical equation: $SO_2 + Na_2O \rightarrow Na_2SO_3$

  • Interaction with Water:

  • Condition: Reacts with all acidic oxides except silicon dioxide ($SiO_2$

  • Products: Oxygen-containing acids

  • Chemical equation: $P_2O_5 + 3H_2O \rightarrow 2H_3PO_4$

• Chemical Properties of Amphoteric Oxides:

  • Interaction with Acids:

  • Products: Salt and water

  • Chemical equation: $ZnO + 2HCl \rightarrow ZnCl_2 + H_2O$

  • Interaction with Acidic Oxides:

  • Products: Salt

  • Chemical equation: $ZnO + SO_3 \rightarrow ZnSO_4$

  • Interaction with Molten Alkalis:

  • Products: Salt and water

  • Chemical equation: $ZnO + 2NaOH \rightarrow Na_2ZnO_2 + H_2O$

Bases: Definition and Nomenclature

• Definition: Bases are complex substances consisting of metal atoms combined with hydroxide groups ($OH$

• Nomenclature Rules for Bases:

  • The systematic name of a base consists of two words: the word "hydroxide" followed by the name of the metal.

  • Examples with fixed metal oxidation states:

    • $NaOH$ — sodium hydroxide

    • $Zn(OH)_2$ — zinc hydroxide

  • If a metal can exist in variable oxidation states and form multiple hydroxides, its oxidation state in that specific base is indicated in parentheses using Roman numerals immediately following the metal's name.