Carbon and its Compounds

• Diamond: Each carbon atom utilizes all four of its valence electrons to form four strong covalent single bonds with four neighboring carbon atoms in a rigid three-dimensional tetrahedral lattice. Because no free or delocalized electrons are left to carry electric charge, diamond is a complete electrical insulator.
• Graphite: Each carbon atom bonds with only three other carbon atoms in a flat hexagonal planar layer. The fourth valence electron remains free and delocalized across the hexagonal planes. Under an applied electrical voltage, these mobile delocalized electrons drift easily across the layers, making graphite an excellent electrical conductor.

• In a closed, unventilated room, the burning coal consumes the available oxygen rapidly.
• As oxygen levels drop, coal burns under incomplete combustion, producing large volumes of Carbon Monoxide gas ($\text{CO}$):

$$2\text{C} + \text{O}_2\text{ (limited)} \to 2\text{CO}$$

• Carbon monoxide is a colorless, odorless, non-irritating "Silent Killer".
• When inhaled, $\text{CO}$ binds with blood hemoglobin $250$ times more strongly than oxygen, forming a stable, non-dissociating complex called Carboxyhemoglobin.
• This blocks the blood from transporting vital oxygen to the brain and body tissues, inducing painless drowsiness, deep coma, and fatal asphyxiation during sleep.

• Stage 1 (Turning Milky):
When $\text{CO}_2$ is first passed into clear lime water ($\text{Ca(OH)}_2$), an insoluble white precipitate of calcium carbonate ($\text{CaCO}_3$) is formed, turning the solution milky:

$$\mathbf{\text{Ca(OH)}_2\text{ (aq)} + \text{CO}_2\text{ (g)} \to \text{CaCO}_3 \downarrow \text{ (white ppt)} + \text{H}_2\text{O (l)}}$$

• Stage 2 (Dissolution of Milkiness with Excess $\text{CO}_2$):
When $\text{CO}_2$ is bubbled continuously for a longer time, the milky precipitate reacts further and dissolves completely, forming soluble calcium bicarbonate ($\text{Ca(HCO}_3)_2$), restoring a crystal-clear solution:

$$\mathbf{\text{CaCO}_3\text{ (s)} + \text{H}_2\text{O (l)} + \text{CO}_2\text{ (g)} \to \text{Ca(HCO}_3)_2\text{ (aq) [clear, soluble]}}$$

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• Catenation: The unique property of carbon atoms to form strong covalent bonds with one another, linking into long continuous chains, branched networks, and closed rings of arbitrary size.
• Tetravalency: The characteristic combining capacity of carbon ($Z = 6$, configuration $2, 4$) having four valence electrons, requiring it to form four covalent bonds with other atoms to achieve a stable octet configuration.

• Laboratory Preparation: By the action of dilute hydrochloric acid on marble chips (calcium carbonate):

$$\mathbf{\text{CaCO}_3\text{ (s)} + 2\text{HCl (aq)} \to \text{CaCl}_2\text{ (aq)} + \text{H}_2\text{O (l)} + \text{CO}_2\text{ (g)} \uparrow}$$

• Why NOT Dilute Sulphuric Acid ($\text{H}_2\text{SO}_4$)?
Dilute $\text{H}_2\text{SO}_4$ reacts initially with marble chips to form insoluble Calcium Sulphate ($\text{CaSO}_4$):

$$\text{CaCO}_3 + \text{H}_2\text{SO}_4 \to \text{CaSO}_4 \downarrow + \text{H}_2\text{O} + \text{CO}_2 \uparrow$$

The insoluble $\text{CaSO}_4$ forms an impermeable crust over the surface of the marble chips, blocking further acid contact and terminating the reaction immediately!

1. Non-Flammable & Non-Supporter: Carbon dioxide is completely non-combustible and does not support the combustion of organic fuels.
   2. Heavier than Air: $\text{CO}_2$ has a vapor density of $22$ (approximately $1.5$ times denser than atmospheric air). When discharged over a fire, it sinks and forms a heavy suffocating blanket over the burning fuel, displacing oxygen and starving the flame of combustion air.

• Fullerenes: A third crystalline allotrope of pure carbon consisting of spheroidal, hollow cage-like clusters of carbon atoms discovered in 1985.
• Buckminsterfullerene ($C_{60}$):
Consists of a hollow spherical cage made of exactly $60$ carbon atoms arranged like a soccer ball (geodesic dome).
The surface contains $20$ regular hexagons and $12$ regular pentagons fused together. Named after architect Buckminster Fuller.

• Greenhouse Effect: The natural warming process where solar shortwave visible light penetrates the atmosphere to warm Earth's surface, but the re-radiated longwave infrared thermal radiation is absorbed and trapped by certain atmospheric gases, keeping the planet habitable.
• Global Warming: Excessive emissions from fossil fuel combustion increase greenhouse gas concentrations, trapping excessive thermal energy and raising global mean temperatures.
• Two Major Greenhouse Gases:
1. Carbon dioxide ($\text{CO}_2$)
2. Methane ($\text{CH}_4$) (also water vapor and nitrous oxide).