Structure, Properties and Uses of Allotropes and Oxides of Carbon

Allotropes of Carbon

Introduction

Allotropes are  elements that exist in  more than one form but are in the same physical state. The Carbon  the sulfur are  two common chemical compound having allotropes. Due to the carbon having valence, carbon can form many allotropes. The known forms of carbon are graphite and diamond. Carbon is a non-metal with the symbol C and atomic number 6. In the modern periodic table, carbon is divided into the second period and the 14th group. The carbon comes from Latin word “carbo” which means “coal”. Diamond, coke ,carbon, graphite, and fullerenes are composed of only carbon elements  and are said to be allotropes of carbon.

The phenomenon in which an element can exist in multiple physical states is called an allotrope. Allotropes of carbon can be divided into two categories:

• Amorphous Carbon Allotropes
• Crystalline Carbon Allotropes

Crystal allotropes of carbon: The four allotropes of carbon with a well-defined crystal structure are:

1. Diamond
2. Graphite
3. Fullerenes
4. Carbon Nanotubes

Amorphous Allotropes of Carbon: Some important amorphous allotropes of carbon are:

1. Coal
2. Coke
3. Wood charcoal
4. Animal charcoal
5. Sugar charcoal
6. Lampblack
7. Gas Carbon

Diamond Structure

Diamond has a three-dimensional network of carbon atoms connected by strong covalent bonds. Each carbon atom is in a sp3 hybrid and is tetrahedral bonded to four adjacent carbon atoms.

This network is extended in three dimensions. All carbon-carbon (C-C) bonds are equal  to 154pm and each C-C-C bond angle is 109∘28′.

Properties of Diamond

• This is the purest and  densest type of carbon. Its density is 3.51gcm–3 
•  It is the most difficult known natural  substance and has a very high melting point (3843K). Insoluble in all solvents.
• It is transparent and handles high refractive index. 
•  It’s the bad conductor of electricity. This is because all  valence electrons of each carbon participate in carbon-carbon sigma (σ) bonds, leaving no unpaired electrons  in the crystal.

Uses of diamond

• Diamonds are used to cut tools such as glass cutters, saws for cutting marbles, and jackhammers.
• Ophthalmologists use sharp diamonds as a tool to remove cataracts from the eye very accurately. The 
• Diamond die is used to pull very fine wires from metals such as tungsten.
• Diamonds are used in the production of jewelry because of their extraordinary brilliance.

Graphite: A Non-metallic Conductor

In graphite, each carbon atom is in a  sp2 hybrid and is covalently bonded to three adjacent carbon atoms  in the same plane. In this way, a flat hexagonal ring is formed. The carbon-carbon bond length of this ring is 142pm. The hexagonal ring forms a layer. Graphite is soft and lubricious because these layers can slide against each other.

Properties of Graphite

• It is a dark gray substance with a metallic luster. 
•  It is very greasy and soft to touch.
• The fourth valence electron of each carbon is free to move, as only three electrons of each carbon are used to make the hexagonal ring of graphite. This makes graphite an excellent conductor of heat and electricity.
• It is not attacked by any of the dilute acids, chlorine and alkali. A mixture of potassium dichromate and sulfuric acid slowly oxidizes it  to carbon dioxide.

Uses of Graphite

• Used in the manufacture of electrodes and carbon arc. 
•  Used as a lubricant for machines operating at high temperatures.
• Used to make pencils. Powdered graphite is mixed with clay and pressed into a stick. These pens are used to make pencils. 
•  Can be used as moderator for the nuclear reactors.

Oxides of Carbon

The Carbon forms two oxides, carbon dioxide CO2 and carbon monoxide (CO). It also forms carbon suboxide, C3O2 

Properties of Carbon Oxides

Carbon oxides, or oxocarbons, are a class of organic compounds that contain only carbon and oxygen. Most basic carbon oxides  are the carbon monoxide and the carbon dioxide. Many other stable and metastable carbon oxides  are known, but  rarely encountered.

Carbon Monoxide

The simplest oxocarbon is carbon monoxide (CO). The Carbon monoxide is a tasteless, colourless gas which is slightly lighter than the air. It is metabolically produced and is said to have some biological functions, but is toxic to humans and animals when encountered at high concentrations.

Carbon monoxide is stabilized by  different three resonant structures. First resonance structure is most important one.

Carbon monoxide is composed of  carbon and  oxygen atoms bonded by  triple bonds. The distance between the carbon and the oxygen atom is 112.8 pm, consistent with the existence of  triple bonds.The CO bond dissociation energy  is 1072 kJ / mol, which represents the strongest known chemical bond. CO has three resonance structures, but the structure with  triple bonds is the structure closest to the actual electron density distribution in the molecule.

CO is naturally produced by the human body as a signal transduction molecule. Its metabolic abnormalities are associated with a variety of illnesses such as hypertension and heart failure. CO is found in small quantities withinside the atmosphere, on the whole due to the burning of fossil fuels and fires. Through herbal techniques withinside the atmosphere, it’s miles finally oxidized to carbon dioxide (CO2).

Carbon Dioxide

Carbon dioxide are naturally occurring linear compound which is composed of two oxygen atoms covalently bonded to the carbon atom. The two C = O bonds are equivalent and short (116.3 pm), which are  corresponding to the double bond. This compound is centrally symmetric, so there is no net dipole. CO2 is colorless. It has an irritating acidic odor at high concentrations, but is odorless at low concentrations. At standard temperature and pressure, the density is 1.98 kg / m3, which is about 1.5 times that of air. At pressures below 520 kPa, it is not in a liquid state. At 1 atm, the gas deposits directly on the solid at temperatures below 78.5 ° C, and the solid sublimates directly  above this temperature. Solid CO2 is called dry ice. The carbon atom at the center of carbon dioxide is bonded to two oxygen atoms by a double bond with a linear structure. Since the molecule is centrally symmetric, there is no net dipole moment. 

CO2 is the end product of the organism’s metabolism through the cellular respiration process, and energy comes from the breakdown of sugars, fats and amino acids.Despite the fact that the human body produces about 2.3 pounds of carbon dioxide per day, it is considered toxic and levels of up to 10 percent can cause choking.

Conclusion

When an element is present in multiple crystalline forms, those forms are called allotropes. The two most common allotropes of carbon are diamond and graphite.The crystal structure of diamond is an infinite three-dimensional array of carbon atoms, each forming an angle equal to the adjacent bond.

Carbon oxides are an important component of the atmosphere and  are part of the carbon cycle. Carbon dioxide is naturally produced by respiration and metabolism and is consumed by plants through photosynthesis.