Key Differences: Physical vs Chemical Properties of Carbon
Carbon is a chemical element that is non-metallic. Its symbol is 'C'. Its atomic number is 6. It belongs to group 14 in the periodic table. Carbon is mainly found in coal deposits; however, the carbon obtained from coal deposits must be processed for its commercial use.
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Carbon is one of the most significant elements on Earth. It is also a major constituent of most organic compounds. Since all the living bodies on Earth are made of mostly organic compounds, they (indirectly, carbon and its compounds) become important for our existence. The human body constitutes about 18% of carbon. Apart from this, carbon has its utility in various domains of technology, also such as in pieces of jewellery, paints, synthetic fibres, production of steel and carbon dating, etc.
Physical Properties and Allotropes of Carbon
The atoms of carbon can be bonded in different ways. They form allotropes of carbon. Allotropes are a different form of an element with a difference in physical properties but a similarity in chemical properties. It occurs in the same physical state in two or more crystalline forms. The most popular among the three allotropes of carbon are graphite and diamond. They both have different crystalline structures.
Differences between Graphite and Diamond:
Graphite: It has three covalent bonds around one carbon atom. It has a planar structure. It is composed of an sp2 hybridised carbon atom. It has a relative density of 2.3. It is black in colour and opaque. It is a good conductor of electricity. It is a very good lubricant and the softest material known and greasy to touch. Certain forms of graphite are used in thermal insulation and certain others in thermal conduction. It burns in air at 700–800oC to give carbon dioxide. It is insoluble in all ordinary solvents.
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Diamond: It occurs naturally in a free state. It is a very stable allotrope of carbon made up of four covalent bonds around one carbon atom. It has a face-centred cubic crystal structure. It is composed of sp3 hybridised carbon atoms. It is transparent and has a high relative density. It also has a high refractive index of 2.45. It is a non-conductor of heat and electricity. Diamond is the hardest natural mineral found until now. It burns in the air at 900oC to give carbon dioxide. It is insoluble in all solvents.
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Both graphite and diamond occur in the solid state. They are both very brittle. The density of different forms of carbon depends upon their respective origin. There is some form of carbon that is pure like coal and some which may not be pure and are mixtures of hydrogen and carbon.
The third allotrope and the purest form of carbon are 'Fullerene’. They have the potential to function as a semiconductor, conductors, and superconductors under certain conditions. They can also change light transmission based on intensity and this is referred to as a photometric effect. They are safe and inert. They also create active derivatives.
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Chemical Properties of Carbon
Chemical properties determine how carbon will react with other substances or change from one form to the other. The chemical properties of carbon are observed during the chemical reactions. Carbon forms millions of compounds.
Carbon takes part in four main reactions:
Combustion Reaction: When carbon burns in air, it gives carbon dioxide, heat, and light. Combustion is referred to as the process in which burning of carbon in excess of oxygen results in the production of heat and light.
C(s) + ½ O2(g) \[\rightarrow\] CO2(g) + heat + light
Unsaturated carbon burns with a yellow flame and produces soot while saturated carbon burns with a blue flame. Combustion could be either complete combustion or incomplete combustion.
In the complete combustion of a hydrocarbon, combustion takes place in excess of oxygen and the final products are carbon dioxide and water. Heat and light are generated in the form of energy. Saturated compounds undergo complete combustion.
On the contrary, incomplete combustion takes place when there is insufficient oxygen and there is an excess of hydrocarbon. It produces products which are carbon monoxide or carbon and water. It also has a smoky flame and produces soot. Unsaturated compounds undergo incomplete combustion.
Oxidation Reaction: Carbon and its compounds are oxidised in the presence of oxygen.
C(s) + ½ O2(g) \[\rightarrow\] 2CO(g)
All combustion reactions are oxidation reactions but all oxidation reactions are not combustion reactions.
Addition Reaction: Carbon has the ability to make long strings or chains of atoms. This is referred to as the addition reaction. Unsaturated compounds undergo this reaction to become saturated.
Example: When ethene which contains a double bond is heated in the presence of hydrogen using a nickel catalyst, it produces ethane.
CH2=CH2 + H2 + (Nickel Catalyst) \[\rightarrow\]CH3 - CH3
Substitution Reaction: The substitution reaction is a reaction in which a functional group in a compound is replaced by another functional group.
Example: CH3Cl + OH- \[\rightarrow\] CH3OH + Cl-
Carbon Isotopes
Carbon-12 (12C): It has six neutrons and six protons. This is the most common isotope. Carbon-12 is highly stable and has a proportion of about 98.89% in a given sample. Hence, it is the major constituent of any sample of carbon.
Carbon-13 (13C): It has seven neutrons and six protons. This carbon isotope is also stable in nature and is heavier than the carbon-12 isotope. The proportion of carbon-13 in a given sample is about 1.11%.
Carbon-14 (14C): It contains eight neutrons and six protons in its nucleus. This isotope is unstable and highly radioactive. However, it decays into a stable product over time. It is heavier than carbon - 12,13 and has a very low proportion in a sample of less than about 10-10 %.
Conclusion
This was a small discussion on carbon, its physical and chemical properties, allotropes of carbon and isotopes, and their percentage occurrence in a given sample, and the importance of carbon.
FAQs on Physical and Chemical Properties of Carbon: Complete Guide
1. What are the key physical properties of carbon?
Carbon is a non-metal that exists as a solid at room temperature. Its physical properties vary significantly depending on its allotropic form:
- Appearance: It can be a black, opaque solid like graphite or a transparent, lustrous crystal like diamond.
- Hardness: Diamond is the hardest known natural substance, while graphite is soft and slippery.
- Electrical Conductivity: Diamond is an electrical insulator, whereas graphite is a good conductor of electricity due to the presence of free electrons.
- Melting and Boiling Points: Carbon has very high melting and boiling points because of the strong covalent bonds between its atoms.
2. What are the most important chemical properties of carbon for Class 10 students?
According to the CBSE syllabus, the main chemical properties of carbon and its compounds are:
- Combustion: Carbon burns in oxygen to produce carbon dioxide, heat, and light. For example, C + O₂ → CO₂.
- Oxidation: Carbon compounds can be easily oxidised. For instance, alcohols can be oxidised to carboxylic acids.
- Addition Reaction: Unsaturated hydrocarbons (with double or triple bonds) undergo addition reactions, typically with hydrogen in the presence of a catalyst, to become saturated.
- Substitution Reaction: Saturated hydrocarbons are relatively unreactive but undergo substitution reactions where one or more hydrogen atoms are replaced by another atom, such as a halogen.
3. What are the allotropes of carbon and how do they differ?
Allotropes are different structural forms of the same element. The main allotropes of carbon are Diamond, Graphite, and Buckminsterfullerene.
- Diamond: Each carbon atom is bonded to four other carbon atoms, forming a rigid three-dimensional tetrahedral lattice. This structure makes it extremely hard.
- Graphite: Each carbon atom is bonded to three other carbon atoms in the same plane, creating hexagonal layers. These layers can slide over one another, making graphite soft and a good lubricant.
- Buckminsterfullerene (C₆₀): Carbon atoms are arranged in the shape of a football, with interlocking hexagonal and pentagonal rings.
4. What makes carbon so unique that it forms the basis of millions of compounds?
Carbon's unique ability to form a vast number of compounds is due to two primary properties:
- Tetravalency: Carbon has a valency of four, meaning each carbon atom can form four covalent bonds with other atoms. This allows for the creation of complex and branched structures.
- Catenation: This is the unique ability of carbon atoms to form strong covalent bonds with other carbon atoms, creating long chains, branched chains, and rings of various sizes. No other element exhibits catenation to this extent.
5. Why do different allotropes of carbon like diamond and graphite have opposite electrical properties?
The difference in electrical conductivity is due to their atomic structure. In diamond, each carbon atom uses all four of its valence electrons to form strong covalent bonds with four other atoms. As there are no free or delocalised electrons, diamond cannot conduct electricity. In graphite, each carbon atom is bonded to only three others in flat layers. The fourth valence electron from each atom is delocalised and free to move between the layers, allowing graphite to conduct electricity.
6. How can you differentiate between a physical and a chemical property using carbon as an example?
A physical property can be observed without changing the chemical identity of the substance, while a chemical property describes how it reacts to form new substances.
- Example of a Physical Property: The hardness of a diamond. You can test its hardness by scratching it against another material without changing the fact that it is still carbon.
- Example of a Chemical Property: The combustion of charcoal (a form of carbon). When it burns in air, it reacts with oxygen to form carbon dioxide, a completely new chemical substance. The original carbon is consumed in this chemical change.
7. How does the property of carbon isotopes lead to real-world applications like carbon dating?
Carbon dating relies on the properties of carbon's isotopes, specifically the stable Carbon-12 and the radioactive Carbon-14. Living organisms constantly absorb both isotopes from the atmosphere. When an organism dies, it stops taking in carbon. The Carbon-14 within its remains begins to decay at a known, constant rate (its half-life). By measuring the ratio of remaining Carbon-14 to Carbon-12 in a sample, scientists can accurately estimate the time that has passed since the organism's death.
