Railway Science (Chemistry-Carbon And its Compound)

Shells in an atom are distinct energy levels where electrons orbit the nucleus. They're organized by energy, with higher-numbered shells located farther from the nucleus. Carbon has two electron shells, with the first holding two electrons and the second holding four out of a possible eight spaces. Carbon (C) - non-metallic, has high melting points. It makes up 18% of the human body. Uses - in making Jewelry like diamonds, inks, paints, and carbon dating.

Cyclohexane (C₆H₁₂) – Homocyclic compound (contains only carbon and hydrogen atoms), clear colorless liquid, petroleum like odour, as a solvent, paint remover, cycloalkane, a volatile organic compound and used to make nylon.

(Founder G.N. Lewis) - Consists of the mutual sharing of one or more pairs of electrons between two atoms. Examples - Hydrogen (H₂), Oxygen (O₂), Nitrogen (N₂), Water (H₂O), and Methane(CH₄). Properties - Powerful chemical bonds, directional, low melting and boiling points, lower enthalpies of vaporization and fusion, don’t conduct electricity, exhibit the phenomenon of isomerism.

Carbon forms strong bonds with most other elements. Due to the small atomic size of carbon enables its nucleus to strongly hold on to the shared pairs of electrons. Allotropes of carbon - Diamond, graphite and buckminsterfullerene. There are four basic types of orbitals: s, p, d, and f present in atoms.

Removing 4 carbon electrons requires overcoming strong electrostatic forces of attraction between the positively charged nucleus and the negatively charged electrons, making it energetically unfavorable.
Tetravalency - atom completes its octet by sharing four electrons with other atoms. Catenation is the ability of elements to form long chains. It is shown by both Silicon and Carbon.

Carbon compounds - Covalent (do not dissociate into ions in aqueous solution and also it does not have free electrons) in nature, poor conductor of electricity (Since there is no flow of charge), low melting points and boiling points. Examples - Hydrogen (H₂), Oxygen (O₂), Nitrogen (N₂), and Methane (CH₄).

The ability of a carbon atom to link with other carbon atoms to form long carbon chains is known as catenation.This is the reason for the presence of the vast number of organic compounds (carbon-based) in nature. As it involves the formation of covalent bonds, it is preferred by the non-metals and not by the metals. Eg: silicon, sulfur, boron, phosphorus etc.

Ionic compounds - formed by complete transfer of electrons from one element to the other. Metals lose electrons and become positive ions (cations) while the non metals receive the electron & become negative ions (anions). Then both the ions are joined together by strong electrostatic forces. Characteristics of ionic compounds - high melting and boiling points, Hard but brittle solids, Dissociate into ions when dissolved in water, Conduct electricity in melted & solution form (but not in solid state).

Carbonisation: conversion of organic matters (plants and dead animal remains) into coal through destructive distillation under high pressure and temperature. Coal is a complex mixture of carbon, hydrogen and oxygen compounds, found in coal mines deep under the surface of earth.
The classification of coal depends on the carbon content of coal. Higher the temperature and pressure of the Earth and the longer time the coal has been buried under the Earth, the more is the carbon content in it. Peat (30-40%) < Lignite (50%) < Bituminous (60%) < Anthracite (>80%).

Graphite - naturally-occurring crystalline allotrope of carbon; soft, brittle and a good conductor of electricity. It has a tetrahedral structure with layers. Uses - to make the lead of pencils, in lubricants like grease, powdered form in paints.