Group 14

Group 14 Elements (Carbon Family)

Members: C, Si, Ge, Sn, Pb (Fl: short-lived synthetic; chemistry not established)
Nature: C (non-metal), Si/Ge (metalloids), Sn/Pb (soft metals)

1) Overview, Occurrence & Importance

• Carbon: Elemental (diamond, graphite, coal); combined (carbonates, hydrocarbons, CO₂ ~0.03% in air). Life-essential; base of organic chemistry.
  Isotopes: ¹²C, ¹³C (stable); ¹⁴C (t½ ≈ 5770 y) → radiocarbon dating.

• Silicon: ~27.7% of crust as silica, silicates; key in glass, ceramics, cement, electronics.

• Germanium: trace; semiconductor.

• Tin (Sn): from cassiterite SnO₂; forms Sn(II)/Sn(IV).

• Lead (Pb): from galena PbS; Pb(II) most stable; Pb(IV) strongly oxidizing.

2) Electronic Configuration, Bonding, and Periodic Trends

• Valence configuration: ns² np² (4 valence e⁻).

• C has only s,p → effective covalency 4. Si–Pb can expand coordination (vacant low-lying d/σ*), forming complexes: [SiF₆]²⁻, [GeF₆]²⁻, [Sn(OH)₆]²⁻.

• Covalent radius: ↑ down group (C ≪ Si < Ge < Sn < Pb).

• Ionisation enthalpy: overall ↓; slight rise at Pb (inert-pair stabilization).

• Electronegativity: C highest; Si ≈ Ge ≈ Sn ≈ Pb nearly constant.

• Physical character:

• Got it — here’s a clean, non-tabular summary of physical-property trends for Group 14 (C, Si, Ge, Sn, Pb), with the order written out and values included (where your source gives numbers).

• Atomic / Covalent Radius (pm) — increases down the group

• C 77 < Si 118 < Ge 122 < Sn 140 < Pb 146

• Reason (brief): more shells; poor d/f shielding moderates the increase near Pb.

• Ionic Radius (pm) — increases down the group

• M⁴⁺: Si⁴⁺ 40 < Ge⁴⁺ 53 < Sn⁴⁺ 69 < Pb⁴⁺ 78
  M²⁺: Ge²⁺ 73 < Sn²⁺ 118 < Pb²⁺ 119
  (C and Si don’t commonly form stable M²⁺ in this context.)

• First Ionization Enthalpy, ΔiH₁ (kJ·mol⁻¹) — generally decreases; slight rise at Pb

• C 1086 > Si 786 > Ge 761 > Sn 708 < Pb 715

• Reason: bigger size & shielding lower IE; inert-pair stabilization nudges Pb slightly upward.

• Electronegativity (Pauling) — drops from C to Si, then ~constant

• C 2.5 > Si 1.8 ≈ Ge 1.8 ≈ Sn 1.8 < Pb 1.9

• Note: small uptick at Pb often ascribed to relativistic effects.

• Density (g·cm⁻³ at ~293 K) — increases down the group

• Si 2.34 < C (diamond) 3.51 < Ge 5.32 < Sn 7.26 < Pb 11.34
  (Your table lists diamond = 3.51; graphite ≈ 2.22 for reference.)

• Melting Point (K) — overall decreases down the group

• C 4373 > Si 1693 > Ge 1218 > Pb 600 > Sn 505
  (Pb slightly above Sn despite being heavier; metallic lattice differences.)

• Boiling Point (K) — overall decreases down the group

• Si 3550 > Ge 3123 > Sn 2896 > Pb 2024
  (Carbon’s b.p. not listed in your table; it sublimes at very high T, hence dash in source.)

• Electrical Resistivity (Ω·cm at 293 K) — drops sharply down the group

• (lower ρ = better conductor)
  C (diamond) ~10¹⁴–10¹⁶ » Si ~50 ≈ Ge ~50 » Sn ~1×10⁻⁵ < Pb ~2×10⁻⁵

• Conductivity order (qualitative):
  C(graphite) < Si < Ge < Sn < Pb
  (Diamond is an insulator; graphite conducts along planes.)

• Hardness — decreases down the group

• C (diamond, hardest) > Si > Ge > Sn > Pb

• Metallic Character & Lustre — increases down the group

• C, Si (non-metals) < Ge (metalloid) < Sn, Pb (metals)

• Physical State at 298 K — all solids

• C, Si: network covalent (hard/brittle)

• Ge: covalent–metalloid (brittle)

• Sn, Pb: metallic (soft; Pb very soft and dense)

• One-line recap

• Down C → Pb: size↑, density↑, metallic nature↑, resistivity↓ (conductivity↑); while ΔiH₁↓ (slight Pb rise), EN↓, m.p./b.p.↓, hardness↓.

• C/Si network solids (very high mp); Ge metalloid; Sn/Pb metals.

Inert-pair effect: reluctance of ns² electrons to bond increases down group → +2 stability ↑ (Ge < Sn < Pb), Pb(IV) oxidizing; Sn(II) reducing.

3) Catenation, Multiple Bonding & Allotropy

• Catenation strength: C » Si > Ge ≈ Sn » Pb
  (Bond enthalpies kJ·mol⁻¹: C–C 348 > Si–Si 297 > Ge–Ge 260 > Sn–Sn 240).

• π-Bonding: Strong for C (C=C, C≡C, C=O, C≡N); weak for heavier (diffuse orbitals).

• Allotropes of Carbon

  • Diamond: sp³, 3D covalent network (C–C 154 pm); hardest; insulator.

  • Graphite: sp² layered; delocalized π → conductor along planes; soft lubricant.

  • Fullerenes (e.g., C₆₀): spherical cages (fused 5/6 rings), sp²; aromatic; “buckyballs”.

4) Oxides: Acid–Base & Reactivity

• Dioxides (MO₂): CO₂, SiO₂, GeO₂ acidic; SnO₂, PbO₂ amphoteric.

• Monoxides (MO): CO neutral; GeO acidic; SnO, PbO amphoteric.

• With Water: C, Si, Ge unaffected; Sn + steam → SnO₂ + H₂; Pb protected by oxide film.

Key reactions (as in your content):

• Tin with steam:
  Sn(s) + 2H₂O(g) → SnO₂(s) + 2H₂(g)

5) Halides, Hydrolysis & Complex Formation

• Tetrahalides (MX₄): mostly covalent, sp³, tetrahedral (except SnF₄, PbF₄ more ionic).

• Dihalides (MX₂): stability increases down group (PbX₂ very stable).

• PbI₄ does not exist (weak Pb–I bond cannot compensate energy to involve 6s² → unstable Pb(IV)); PbF₄ can exist (strong Pb–F).

• Hydrolysis: SiCl₄/GeCl₄/SnCl₄ readily hydrolyze; CCl₄ resists (no accessible acceptor orbitals on C).

Reactions to include (placed here):

• SiCl₄ hydrolysis (overall to silica):
  SiCl₄(l) + 2H₂O(l) → SiO₂(s) + 4HCl(aq)
  or via orthosilicic acid:
  SiCl₄ + 4H₂O → Si(OH)₄ + 4HCl; nSi(OH)₄ → (SiO₂)ₙ + 2nH₂O

• Hexafluorosilicate formation:
  SiF₄(g) + 2F⁻(aq) → [SiF₆]²⁻(aq)

6) Key Compounds of Carbon: CO and CO₂

A) Carbon Monoxide (CO)

Preparation (all included):

1. Limited O₂: 2C(s) + O₂(g) → 2CO(g)

2. Lab (formic acid, 373 K, conc. H₂SO₄): HCOOH → H₂O + CO

3. Water gas (synthesis gas), 473–1273 K: C + H₂O(g) → CO + H₂

4. Producer gas (with air): 2C + O₂ + 4N₂ → 2CO + 4N₂

Reductions (metallurgy):

• Fe₂O₃ + 3CO → 2Fe + 3CO₂

• ZnO + CO → Zn + CO₂

Notes: Colorless, odorless, poorly soluble; strong ligand (metal carbonyls; lone pair on C); toxic—binds Hb ~300× stronger than O₂.

B) Carbon Dioxide (CO₂)

Preparation (all included):

• Complete combustion: C + O₂ → CO₂; CH₄ + 2O₂ → CO₂ + 2H₂O

• Lab (carbonate + acid): CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

• Industrial (calcination): CaCO₃ → CaO + CO₂

Acid–base / Biology:

• H₂CO₃ formation, buffer:
  H₂CO₃ + H₂O ⇌ HCO₃⁻ + H₃O⁺; HCO₃⁻ + H₂O ⇌ CO₃²⁻ + H₃O⁺ (blood pH ~7.26–7.42).

• Photosynthesis (overall):
  6CO₂ + 12H₂O ⟶ C₆H₁₂O₆ + 6O₂ + 6H₂O (light, chlorophyll)

• Uses: dry ice (refrigeration), fire extinguishers, beverage carbonation, urea manufacture.

• Structure: linear, sp on C; two σ + two pπ–pπ; equal C–O bonds; non-polar.

7) Silicon Dioxide (SiO₂): Structure & Reactions

• Structure: giant 3D network of corner-shared SiO₄ tetrahedra (quartz, cristobalite, tridymite).

• Chemically resistant; attacked by HF and hot alkali.

Reactions (inserted here):

• With HF: SiO₂ + 4HF → SiF₄ + 2H₂O

• With alkali: SiO₂ + 2NaOH → Na₂SiO₃ + H₂O

Uses: glass/ceramics, piezoelectric quartz (precision timekeeping), silica gel (drying, chromatography).

8) Hydrides of Group 14 (from PPTX + core text)

• Hydrocarbons (C hydrides):

  • Alkanes: CₙH₂ₙ₊₂

  • Alkenes: CₙH₂ₙ

  • Alkynes: CₙH₂ₙ₋₂

• Silanes: SiₙH₂ₙ₊₂ (n < 9 mentioned in slides); SiH₄ is readily attacked by water (representative):
  SiH₄ + 2H₂O → SiO₂ + 4H₂ (overall)

• Germanes: GeₙH₂ₙ₊₂ (as per slide)

• Stannane (SnH₄): SnH₄ → Sn + 2H₂ (on heating; slides note ≳145 °C)

(Hydride stability generally decreases down the group; silanes/germanes are moisture-sensitive; stannane thermally labile.)

9) Carbides of Group 2 with Carbon ( “Salt-like carbides”)

Industrial carbothermal routes (high T, often electric arc; slides note 1900–2000 °C, 2200–2050 °C ranges):

• 2BeO + 3C → Be₂C + 2CO

• CaO + 3C → CaC₂ + 2CO

(Strongly endothermic; products Be₂C, CaC₂ are salt-like carbides.)

10) Silicones (Organosiloxanes): Preparation & Properties

• Repeat unit: –[R₂Si–O]–ₙ (R = alkyl/aryl).

• Route (from slides/text):

  1. Hydrolysis of dimethyldichlorosilane:
     (CH₃)₂SiCl₂ + 2H₂O → (CH₃)₂Si(OH)₂ + 2HCl

  2. Condensation polymerization:
     n (CH₃)₂Si(OH)₂ → –[–(CH₃)₂Si–O–]ₙ– + nH₂O

  3. End-capping (chain control):
     (CH₃)₃SiCl + H₂O → (CH₃)₃SiOH + HCl, then
     (CH₃)₃Si–O–[–Si(CH₃)₂–O–]ₙ–Si(CH₃)₃ + nH₂O

• Properties/uses: hydrophobic, thermally stable, good dielectrics; sealants, greases, insulators, biomedical implants.

11) Fullerene Ring Counting: General Formulas (with derivation)

For a spherical trivalent (3-connected) carbon network with only pentagons and hexagons (classical fullerene Cₙ):

Final ring-count formulas for classical fullerenes Cₙ:

• Number of 5-membered rings (pentagons): F₅ = 12

• Number of 6-membered rings (hexagons): F₆ = (n/2) − 10

Checks:

• C₆₀: F₆ = 60/2 − 10 = 20; F₅ = 12 (soccer ball).

• C₇₀: F₆ = 35 − 10 = 25; F₅ = 12.

12) Key points

• PbI₄ vs PbF₄: Pb–I weak → can’t “activate” 6s² to Pb(IV); Pb–F strong → PbF₄ viable.

• SiCl₄ hydrolyzes; CCl₄ doesn’t: Si can accept lone pairs into vacant acceptor orbitals (expanded coordination); C cannot.

• CO dual nature: strong ligand (metal carbonyls) and toxic (binds Hb ~300× O₂).

• SiO₂ resistance: robust 3D Si–O network; only HF (forming SiF₄) and strong base at high T disrupt.

13) Silicates: Structure, Types, and General Formulas

🔹 1. Definition & Basic Unit

Silicates are compounds in which silicon atoms are tetrahedrally coordinated to four oxygen atoms forming SiO₄⁴⁻ units.

Each tetrahedron can:

• exist isolated, or

• share oxygen atoms with adjacent tetrahedra.

The type of sharing (none, corner, edge, or all) determines the class of silicate.

Basic tetrahedral unit: SiO₄⁴⁻

🔹 2. Classification of Silicates

(a) Orthosilicates / Nesosilicates (Isolated Tetrahedra)

• Structure: No oxygen sharing; independent SiO₄⁴⁻ tetrahedra.

• General formula: [SiO₄]⁴⁻

• Ratio (Si : O) = 1 : 4

• Examples:

  • Olivine – (Mg,Fe)₂SiO₄

  • Zircon – ZrSiO₄

(b) Pyrosilicates / Sorosilicates (Double Tetrahedra)

• Structure: Two SiO₄ units share one oxygen atom.

• Basic unit: [Si₂O₇]⁶⁻

• Ratio (Si : O) = 2 : 7 = 1 : 3.5

• Examples:

  • Hemimorphite – Zn₄Si₂O₇(OH)₂·H₂O

  • Thortveitite – Sc₂Si₂O₇

(c) Cyclic Silicates / Ring Silicates

• Structure: 3, 4, or 6 SiO₄ tetrahedra share two oxygens each, forming rings.

• General formula: [SiₙO₃ₙ]²ⁿ⁻

• Ratio (Si : O) = 1 : 3

• Examples:

  • Beryl – Be₃Al₂Si₆O₁₈ (six-membered ring)

  • Tourmaline (complex borosilicate)

(d) Chain Silicates (Inosilicates)

(i) Single Chain Silicates

• Structure: Each tetrahedron shares two oxygens, forming infinite linear chains.

• General formula:  (SiO₃)ₙ²⁻

• Ratio (Si : O) = 1 : 3

• Examples:

  • Pyroxenes – e.g. MgSiO₃, CaMg(Si₂O₆)

(ii) Double Chain Silicates

• Structure: Two single chains link by sharing oxygens.

• General formula: [Si₄O₁₁]ₙ6-

• Ratio (Si : O) = 4 : 11 = 1 : 2.75

• Examples:

  • Amphiboles – e.g. Ca₂Mg₅Si₈O₂₂(OH)₂

(e) Sheet Silicates (Phyllosilicates)

• Structure: Each tetrahedron shares three oxygens, forming two-dimensional sheets.

• General formula:  (Si₂O₅)ₙ²⁻

• Ratio (Si : O) = 2 : 5 = 1 : 2.5

• Examples:

  • Micas (M₂₋₃Si₄O₁₀(OH)₂) – e.g. Muscovite, Biotite

  • Talc – Mg₃Si₄O₁₀(OH)₂

  • Kaolinite – Al₂Si₂O₅(OH)₄

→ 2D layers with interlayer cations (Mg²⁺, K⁺, etc.)

(f) Framework Silicates (Tectosilicates)

• Structure: All four oxygens in each SiO₄ are shared → 3D network.

• General formula: [SiO₂]⁰

• Ratio (Si : O) = 1 : 2

• Examples:

  • Quartz – SiO₂

  • Feldspars – MAlSi₃O₈ (M = K, Na, Ca)

  • Zeolites – aluminosilicate frameworks (e.g. Na₂Al₂Si₃O₁₀·2H₂O)

  4. Additional Notes

• Aluminosilicates: When Al³⁺ replaces Si⁴⁺, overall framework gains a negative charge, balanced by cations (Na⁺, K⁺, Ca²⁺).

• Zeolites: Porous aluminosilicates used as ion-exchangers, molecular sieves, and petrochemical catalysts (e.g. ZSM-5 → converts alcohols to gasoline).

• Silica Polymorphs: Quartz, tridymite, and cristobalite interconvert at different temperatures.