Nonmetallic Elements and Their Compounds

Overview of Nonmetallic Elements

• Periodic Table Placement:

  • Hydrogen (Group 1A): Although located in Group 1, hydrogen is a nonmetal.

  • Groups 13-18: Nonmetals are primarily located in the upper right-hand side of the periodic table, including Groups 3A to 7A and the Noble Gases (8A).

  • Metalloids: Found along the "stair-step" line dividing metals and nonmetals. Examples include B, Si, Ge, As, Sb, Te, and At.

  • Classification of Hydrides:

    1. Ionic Compounds: Formed with Group 1A (e.g., $LiH$, $KH$, $RbH$, $CsH$) and Group 2A (e.g., $CaH_2$, $SrH_2$, $BaH_2$).

    2. Polymeric Structures (Covalent): Formed by elements like Be ($BeH_2$) and Al ($AlH_3$).

    3. Discrete Molecular Units: Formed by nonmetals in Groups 14-17 (e.g., $CH_4$, $NH_3$, $H_2O$, $HF$, $SiH_4$, $PH_3$, $H_2S$, $HCl$, etc.).

Hydrogen: Production, Isotopes, and Reactions

• Industrial Production of Hydrogen ($H_2$):

  • Steam Reforming of Hydrocarbons (e.g., Propane): $C_3H_8 (g) + 3H_2O (g) \rightarrow 3CO (g) + 7H_2 (g)$.

  • Coal Gasification: $C (s) + H_2O (g) \rightarrow CO (g) + H_2 (g)$. The resulting mixture of $CO$ and $H_2$ is known as synthesis gas or syngas.

• Laboratory Production:

  • Reaction of active metals with acid: $Zn (s) + 2HCl (aq) \rightarrow ZnCl_2 (aq) + H_2 (g)$.

• Isotopes of Hydrogen:

  1. Hydrogen ($^1H$): The most common isotope.

  2. Deuterium ($^2H$ or D): Found in "heavy water" ($D_2O$).

  3. Tritium ($^3H$ or T): Radioactive isotope.

• Kinetic Isotope Effect (KIE):

  • Substitution of deuterium for hydrogen affects reaction rates and equilibrium constants due to the difference in mass.

  • Example (Acidity of Acetic Acid):

    • Protonated Acetic Acid: $CH_3COOH (aq) \rightleftharpoons CH_3COO^- (aq) + H^+ (aq)$, where $K_a = 1.8 \times 10^{-5}$.

    • Deuterated Acetic Acid: $CH_3COOD (aq) \rightleftharpoons CH_3COO^- (aq) + D^+ (aq)$, where $K_a = 6 \times 10^{-6}$.

• Hydrogenation:

  • The addition of $H_2$ to compounds containing multiple bonds (unsaturated compounds).

  • Requires a catalyst like Platinum (Pt) supported on aluminium oxide ($Al_2O_3$).

  • Process Detail: The Pt surface serves as an active site where $H_2$ molecules dissociate into atoms before adding across a carbon-carbon double bond ($C=C$).

  • Application: Converting unsaturated fats (liquid oils) into saturated fats (solid fats).

The Hydrogen Economy and Metallic Hydrogen

• The Hydrogen Economy:

  • Involves the combustion of hydrogen: $2H_2 (g) + O_2 (g) \rightarrow 2H_2O (l)$.

  • Fuel Values (Comparative Energy Content in $kJ/g$):

    • Hydrogen: $142$

    • Natural gas: $49$

    • Gasoline: $48$

    • Crude oil: $45$

    • Coal: $31$

    • Wood (pine): $18$

• Metallic Hydrogen:

  • Under extreme pressures, hydrogen transitions from a molecular gas to a metallic state.

  • Jupiter's Composition: The interior of Jupiter consists of layers including insulating molecular hydrogen, metallic molecular hydrogen, metallic atomic hydrogen, and a rock core.

Carbon and Synthetic Gas Production

• Phase Diagram of Carbon:

  • Contains regions for Graphite (stable at standard conditions), Diamond (stable at high pressures), Liquid phase, and Vapor phase.

  • Thermodynamic Stability: $C(\text{diamond}) \rightarrow C(\text{graphite})$ has a $\triangle G^\text{o} = -2.87 \text{ kJ}$, indicating graphite is more stable at room temperature and pressure.

• Syngas and Coal Gasification Reactions:

  1. Coal Gasification: $C (s) + H_2O (g) \rightarrow CO (g) + H_2 (g)$.

  2. Methane Formation: $C (s) + 2H_2 (g) \rightarrow CH_4 (g)$.

  3. Methanol Synthesis: $CO (g) + 2H_2 (g) \rightarrow CH_3OH (l)$.

  4. Steam Reforming: $CH_4 + H_2O \rightarrow CO + 3H_2$ (Produces a $1:3$ ratio of $CO$ to $H_2$).

  5. Water Gas Shift Reaction: $CO + H_2O \rightarrow CO_2 + H_2$.

  6. Direct Steam Reforming: $CH_4 + 2H_2O \rightarrow CO_2 + 4H_2$.

Nitrogen and Phosphorus

• Common Compounds of Nitrogen and their Oxidation States:

  • $-3$: Ammonia ($NH_3$)

  • $-2$: Hydrazine ($N_2H_4$)

  • $-1$: Hydroxylamine ($NH_2OH$)

  • $0$: Nitrogen ($N_2$)

  • $+1$: Nitrous oxide ($N_2O$)

  • $+2$: Nitric oxide ($NO$)

  • $+3$: Nitrous acid ($HNO_2$)

  • $+4$: Nitrogen dioxide ($NO_2$)

  • $+5$: Nitric acid ($HNO_3$)

• Ammonium Nitrate ($NH_4NO_3$):

  • Used as an Explosive Fertilizer. Fertilizers generally contain Nitrogen (N), Phosphorus (P), and Potassium (K).

  • Decomposition at T > 250^{\circ} \text{C}: $NH_4NO_3 (g) \rightarrow N_2O (g) + 2H_2O (g)$.

  • Decomposition at T > 300^{\circ} \text{C}: $2NH_4NO_3 (g) \rightarrow 2N_2 (g) + 4H_2O (g) + O_2 (g)$.

• Phosphorus Production and Forms:

  • Produced from phosphate rock: $2Ca_3(PO_4)_2 (s) + 10C (s) + 6SiO_2 (s) \rightarrow 6CaSiO_3 (s) + 10CO (g) + P_4 (s)$.

  • White Phosphorus ($P_4$): Highly reactive; individual tetrahedral units.

  • Red Phosphorus ($(P_4)_n$): Polymeric form; more stable than white phosphorus.

• Phosphorus Oxides and Oxoacids:

  • Oxides: $P_4O_6$ and $P_4O_{10}$.

  • Condensation Reaction: Formation of polyphosphoric acid from phosphoric acid: $3H_3PO_4 \rightarrow H_5P_3O_{10} + 2H_2O$.

Oxygen and Ozone

• Forms of Oxygen Anions:

  • Oxide ($O^{2-}$): Forms base when dissolved: $O^{2-} (aq) + H_2O (l) \rightarrow 2OH^- (aq)$.

  • Peroxide ($O_2^{2-}$): Found in compounds like $H_2O_2$ (Hydrogen peroxide), which is more reactive and lacks one electron compared to a standard oxide structure.

  • Superoxide ($O_2^-$): Extremely reactive species.

• Ozone ($O_3$):

  • Formation: $3O_2 (g) \rightarrow 2O_3 (g)$. This is a non-spontaneous reaction with $\triangle G^\text{o} = 326.8 \text{ kJ}$.

  • Produced via electrical discharge.

  • Acts as a powerful oxidizing agent.

Sulfur

• Extraction Processes:

  • Frasch Process: Uses three concentric pipes to pump superheated steam ($165^{\circ} \text{C}$) into sulfur deposits to melt them (Sulfur m.p. = $115^{\circ} \text{C}$) and bring them to the surface with compressed air. Produces $99-99.8\%$ pure sulfur.

  • Sicilian Method: Traditional manual mining.

• Claus Process (Desulfurization):

  • Converts hydrogen sulfide ($H_2S$) from industrial gas into elemental sulfur.

  • Reaction 1: $2H_2S + 3O_2 \rightarrow 2SO_2 + 2H_2O$.

  • Reaction 2: $2H_2S + SO_2 \rightarrow 3S + 2H_2O$.

• Common Sulfur Compounds:

  • $-2$: Hydrogen sulfide ($H_2S$)

  • $0$: Elemental Sulfur ($S_8$)

  • $+1$: Disulfur dichloride ($S_2Cl_2$)

  • $+2$: Sulfur dichloride ($SCl_2$)

  • $+4$: Sulfur dioxide ($SO_2$)

  • $+6$: Sulfur trioxide ($SO_3$)

Halogens

• Elemental Properties (F, Cl, Br, I):

  • Fluorine ($F$): Pale-yellow gas; highest electronegativity ($4.0$); highest standard reduction potential ($2.87 \text{ V}$).

  • Chlorine ($Cl$): Yellow-green gas.

  • Bromine ($Br$): Red-brown liquid.

  • Iodine ($I$): Dark-violet vapor/Dark metallic-looking solid; lowest ionization energy among halogens listed ($1003 \text{ kJ/mol}$).

• Production of Halogens:

  • Fluorine: Electrolytic production from HF: $2HF \rightarrow H_2 (g) + F_2 (g)$.

  • Chlorine (Laboratory): Oxidation of chloride ions using agents like manganese dioxide or potassium permanganate.

    • With $MnO_2$: $MnO_2 (s) + 2H_2SO_4 (aq) + 2NaCl (aq) \rightarrow MnSO_4 (aq) + Na_2SO_4 (aq) + 2H_2O (l) + Cl_2 (g)$.

    • Handwritten variant: $MnO_2 + 4HCl \rightarrow MnCl_2 + Cl_2 + 2H_2O$.

    • With $KMnO_4$: $2KMnO_4 + 16HCl \rightarrow 5Cl_2 + 2MnCl_2 + 8H_2O + 2KCl$.

  • Chlor-Alkali Process (Industrial): Electrolysis of brine ($NaCl$ solution) to produce chlorine gas, hydrogen gas, and sodium hydroxide ($NaOH$).

• Halogen Compounds and Bleach:

  • Oxoacids: Includes Hypohalous acid (e.g., $HClO$), Halous acid ($HClO_2$), Halic acid ($HClO_3$), and Perhalic acid ($HClO_4$).

  • Bleach (Sodium Hypochlorite, $NaOCl$): Produced by reacting chlorine gas with sodium hydroxide solution: $Cl_2 (g) + 2NaOH \rightarrow NaCl + NaOCl + H_2O$. Household bleach usually contains $3-6\%$ $NaOCl$.