Carbon

The computer screen on which you are reading this article, the clothes

that you are wearing, the food that you eat and even the cars in which

you ride all have one thing in common. What is this thing? They all

are comprised of some element of carbon. Actually, all organic things

are made up of carbon. This is why the study of carbon and its

components is so important.

More About Carbon

The origin of the name ‘carbon’ is a Latin word ‘carbo’ which means

charcoal. This may come as a surprise to you, but it is the fourth most

abundant element in the entire universe. And it is the second most

abundant element in our bodies, the first being oxygen. As a matter of

fact, all organic substances in the world contain carbon in some form

or element, which is why it is the base for the entire branch of organic

chemistry.

Carbon Atom

The atomic number of carbon is 6, which represents the number of

electrons. It is represented by the symbol C and is a non-metal. It has

6 protons, 6 neutrons and obviously 6 electrons. A carbon atom is

considered to be special and unique because it can bond with other

carbon atoms to an almost unlimited degree. It is because its atom is

very small in size and can conveniently fit in as a part of larger

molecules. Each of its atoms has four electrons in its outer shell called

valence electrons and can form for chemical bonds with other atoms

and molecules.

Physical Properties of Carbon

The physical properties of this element vary according to its

allotropes. The two major allotropes are diamond and graphite. These

two have almost opposing physical properties.

● Whereas diamond is transparent and has no colour, graphite is

opaque and black

● Diamond is the hardest substance known to man, graphite is

soft and spongy in texture

● Now diamond cannot conduct electricity at all, graphite is a

very good conductor of electricity

● Both allotropic elements are solid, non-gaseous

● Also both diamond and graphite are insoluble in water

● It does not melt when heated, it sublimes which is it turns to

gaseous form

Uses of Carbon in daily life

Now you may not even notice but carbon is used in so many daily

activities. Some of the most important uses are:

● It makes up for 18% of the human body. Sugar, glucose,

proteins etc are all made of it. The food we eat contains an

important source of energy which we call carbohydrates.

Carbohydrates are nothing but elements of carbon itself.

● Carbon in its diamond form is used in jewellery. But diamonds

are also used for industrial purposes. It is the hardest substance

known to man and so has many uses in manufacturing

processes.

● Amorphous carbon is used to make inks and paints. It is also

used in batteries.

● Graphite is used as the lead in your pencils. It is also used in

the production of steel.

● One of the most important uses is carbon dating. We can

actually use carbon to measure the age of things. Scientists use

a rare form of carbon called Carbon-14 to measure the age of

fossils, bones etc. The release of this carbon-14 is recorded to

estimate the life of the said organic substance. This is how

scientists find the age and period of dinosaur bones and fossils!

So as you can see from the facts given above carbon is an interesting

element with uncountable uses. This is why a detailed study of it is

essential in Chemistry.

Solved Example for You

Q: Two adjacent layers in graphite are bonded by comparatively

_______ forces.

a. Strong

b. Weak

c. Loose

d. None of the above

Solution: The correct answer is option “b”. Graphite is an allotrope of

carbon. Each atom is covalently bonded to the other three atoms.

These layers slid over each other easily because of the weak Van der

Walls forces between them.

Versatile nature of Carbon

Carbon in its various forms has been known since ancient times in the

form of soot, charcoal, graphite and diamonds. Its name is derived

from a Latin word “carbo” which means “charcoal”. Ancient cultures

did not realize, of course, that these substances were different forms of

the same element. Let us explore the versatile nature of carbon.

Versatile Nature of Carbon

But what makes Carbon such an interesting element can be directly

attributed to its two unique properties, i.e. tetra-valency and

catenation. It is because of these properties that the element has the

capacity to form a large number of compounds. Not only is carbon the

fourth most abundant element in the universe, it has so far more than

three million compounds know to us till date.

The following is a deeper understanding of how these unique

properties of tetra-valency and catenation result in a highly versatile

nature of carbon:

Tetra-valency of Carbon

(Source: Wikipedia) Versatile Nature of Carbon

Carbon has the atomic number of 6, meaning each carbon atom has a

total of six electrons. Two are in the completed inner orbit, while four

electrons are found in the atom’s outermost orbit. This basically

means that carbon has four valence electrons (outer electrons that are

available for forming bonds with other atoms). Because of this

arrangement within the atom’s orbits, carbon is called tetravalent.

The carbon’s four valence electrons can be shared by other atoms (that

have electrons to share), thus forming what we call covalent bonds

(shared electrons bonds). The carbon atom also has the ability to form

a bond with other carbon atoms to create covalent bonds forming long

strings of carbon atoms, bonded to each other like links in a chain.

Silicon (Si), another element in group 14 of the periodic table, also has

four valence electrons and can make large molecules called silicones.

But due to its higher atomic number (in comparison to Carbon), its

atoms are too large to fit together into as great a variety of molecules

as carbon atoms can.

What makes carbon unique is its ability in forming covalent bonds

which are very strong in nature. The small size of the carbon atom

makes the compounds of Carbon exceptionally stable. Hence carbon

as an element has the ability to form a variety of stable compounds,

which can exist freely in nature.

Example: saturated hydrocarbons like Propane and Ethane.

Learn more about different types of Carbon Compounds here.

Catenation

The linkage of atoms of the same elements to form longer chain is

called CATENATION.

Carbon due to its tetravalent nature has the unique property to form

bonds with other atoms of carbon forming a long chain. Because of its

property of catenation, carbon can form a

● Straight chain

● Branched chain

● Cyclic ring

The astounding compound-forming ability of the element comes from

the capacity of its atoms bind to each other not only in straight chains

but in complex branchings, like the branches of a tree. They can join

in a “head-to-tail” structures to make rings of carbon atoms. The

element has practically no limit to the number or complexity of the

branches or the number of rings that can be attached to them, thus

making it unique as there is no limit to the number of different

molecules that can be formed.

Carbon atoms have the ability to share not only a single electron with

another atom forming a single bond, but it can also share two or three

electrons, forming a double or triple bond.This characteristic of carbon

allows it to form a high number of possible bond combinations at

different places, making a huge number of different possible

molecules. What is important to remember is that a molecule that

differs from even a single atom or bond position, becomes a molecule

of a different compound with different physical and chemical

properties.

Examples ● Methyl iodide (CH3-I) and Methylene iodide(CH2-l2), both

differ only in the single bond and double bond aspect, but the

properties vary distinctly and have different uses.

● Methyl iodide (CH3-I) is used as a pre-plant biocide to control

insects like a pesticide, while Methyl iodide (CH2-l2) is used as

an optical contact liquid, for determining the refractive index of

certain gemstones.

Solved Example for You

Q: A molecular formula of cyclo-hydrocarbon is similar to the

molecular formula of which of the following?

a. Alkane

b. Alkene

c. Alkyne

d. None of the above

Sol: The correct answer is option ‘b’. Cyclo-hydrocarbons have two

hydrogen atoms less than straight chain alkane. Similarly, alkenes also

have two hydrogen atoms less than alkanes.

Some Important Carbon Compounds

Carbon is a crucial element of our world. Everything that surrounds is

probably a compound of carbon. Foods, fuels, textiles, drugs

everything is either a compound of carbon or its substituent. So let us

study about some important carbon compounds.

What are Carbon Compounds?

Carbon compounds are compounds whose molecules contain a carbon

atom. They are chemical substances where a carbon atom has bonded

to an atom of another element. These compounds are generally

organic in nature. However many students are under the false

impression can if a molecule contains carbon it implies that it is

organic in nature. This is incorrect. There are various inorganic carbon

compounds as well like for example CO2 (carbon dioxide).

Now carbon compounds can be broadly divided into two categories :

Saturated Carbon Compounds

Carbon compounds that are satisfied by a single bond between them

are saturated compounds. An example of this is Ethane which is C2H6.

Here the duplet or octet of both the atoms is fully complete by only a

single bond.

Unsaturated Carbon Compound

Atoms that are satisfied only by double or triple bonds are unsaturated

carbon compounds. Ethene C2H4 is an unsaturated carbon compound,

it has a double bond.

Types of Carbon Compounds

Now let us take a look at the various types of Compounds

Organic Compounds

This is the biggest class of carbon compounds. An organic compound

must contain carbon and hydrogen. The four major categories of

organic compounds that are present in all living things are

carbohydrates, lipids, proteins and nucleic acid.

Inorganic Carbon Compounds

It is not necessary that the presence of a carbon means the compound

has to be classified as organic. Inorganic carbon compounds are rarer

than organic compounds, but they do occur. They are mostly found in

minerals and other natural sources, Some examples of inorganic

compounds are carbon disulfide (CS2), Hydrogen Cyanide (HCN) and

the most obvious one’s carbon dioxide and carbon monoxide. A few

of these inorganic carbon compounds are

● Carbites: Binary compounds formed with the atoms of carbon

and another element with an electronegativity lower than

carbon. An example would be Titanium Carbide.

● Carbonates: A carbonate is a salt of a carbonic acid. The most

common one is Calcium Carbonate CaCO3

● Cyanides: Chemical compound that contains the cyano group.

It is a carbon atom triple-bonded to a nitrogen atom. An

example would be Sodium Cyanide.

Organometallic Compounds

Compounds formed with a carbon-metal bond are known as

organometallic compounds. They are ionic compounds and are very

polar bonds due to the electropositive nature of metals.

Carbon Allotropes

Allotropes are all different physical forms of the same element. The

atoms of the element are bonded differently and this gives them

different physical and chemical properties. Like coal, graphite and

diamond are all allotropes of the carbon atom.

Carbon Alloys

Pure metals are smelted, in which coke is used as a fuel and reducing

agent. This leads to many alloys having an element of carbon in them.

The carbon steel is one such example where iron is alloyed with

carbon.

Alcohol Production: Ethanol

(Source: Wikipedia)

All alcoholic beverages in the world are actually a form of carbon

compounds. Alcoholic beverages are actually made by adding

Ethanol. The process of fermentation is used to produce ethanol

(alcohol) from glucose. One molecule of glucose gives ethanol and

carbon dioxide as by-products. So alcohols actually contain

carbohydrates.

Solved Example for You

Q: Alcoholic beverages contain which of the following?

a. Glycerol

b. Ethyl Alcohol

c. Methyl Alcohol

d. Isopropyl Alcohol

Sol: The correct answer is option “b”. Alcohol beverages contain ethyl

alcohol (ethanol), Alcohol by volume is a standard measure of how

much ethyl alcohol is contained in a given volume of an alcoholic

beverage.

Chemical properties of Carbon Compounds

Carbon is a fascinating element. It is known to form almost ten million

different compounds most of which are chemical compounds that are

organic in nature. Let us learn a bit about the chemical properties of

carbon compounds.

All carbon compounds show some common characteristic properties.

Let us see the chemical properties of carbon compounds. Four

important chemical reactions are discussed below:

Combustion Reactions:

When Carbon and its compounds burn in the presence of Oxygen (or

air), they give CO2, heat and light.The process of burning carbon and

its compounds in excess of oxygen for the release of heat and light

(energy) is known as combustion.

Following are some of the examples of the combustion reaction of

organic compounds:

C + O2 ⇨ CO2 + Heat + Light

C3H8 + 5O2 = 3CO2 + 4H2O.+ Heat + Light

(C3H8 is the molecular formula for Propane, a common gas present in

LPG which we burn for cooking in our kitchens).

In General, saturated hydrocarbons burn with a clear blue flame,

whereas unsaturated hydrocarbons burn with a yellow flame

producing soot (carbon).

Combustion of hydrocarbons may be of two types: Complete

combustion and incomplete combustion.

Complete combustion of hydrocarbons occurs in excess of

oxygen(air), producing CO2 and H2O as the only final chemical

products.Heat and light (clear blue flame) as a form of energy is

generated.

Incomplete combustion occurs when there is insufficient Oxygen(air)

and the hydrocarbon is in excess.This reaction burns with a sooty or

smokey flame and produces products which are CO(g) and/or C(s) and

H2O.

Oxidation Reactions:

In a combustion reaction, carbon compounds are oxidized in the

presence of oxygen. Though combustion is generally an oxidation

reaction, not all oxidation reactions are combustion reactions.

Oxidation is also carried out by using oxidizing agents (Oxidants).

Oxidizing agents, also referred as Oxidants are substances that oxidize

other substances while undergoing reduction themselves.

Alcohols undergo oxidation in presence of Oxidants like alkaline

potassium permanganate (KMnO4) to form carbolic acids.

Example: Ethanol undergoes oxidation to produce Acetic acid when

heated by an Oxidizing agent like alkaline KMnO4.

Addition reactions:

Unsaturated organic compounds, like alkenes and alkynes, contain

multiple bonds (C=C, C≡C) between their carbon atoms.They undergo

addition reactions to become saturated in nature.

The formation of larger molecules by addition of more radicals is

known as addition reaction.During an addition reaction of unsaturated

organic compounds, a reagent takes place at the double bonded or a

triply bonded carbon atoms.

For example; ethene is converted into ethane when heated with the

catalyst nickel.

CH2=CH2 + H2 + (Nickel catalyst) ⇨ CH3−CH3

Nickel acts as a catalyst, which basically regulates (increase/decrease)

the rate of a given reaction, without itself undergoing any chemical

change.

When ethene undergoes an addition reaction with chlorine, it gives

dichloroethane.

Chlorine is a halogen, whose atoms partially break the carbon-carbon

double bond in the alkene to a single bond and add itself across it.

Substitution Reaction:

A Substitution reaction is one in which an atom or a group of

atoms(functional group) in the compound are replaced by another

atom (or group of atoms). Substitution reactions are single

displacement reactions.

Alkanes, which have only single bonds between their carbon atoms,

are saturated hydrocarbons.They are chemically least reactive.They

are also called paraffin, as they have no affinity (minimum

affinity)towards chemical changes (parum=little;

affins=affinity).However, under suitable conditions, they undergo

substitution reactions.

For example, under the presence of Sunlight, Methane reacts with

chlorine gas to produce chloromethane and hydrogen chloride.

CH4 + Cl2 + Sunlight ⇨ CH3Cl + HCl

Sunlight (UV Light) breaks down the chlorine into free radicles,

which initiates the substitution reaction.

These reactions define the chemical properties of carbon compounds.

Solved Examples for You

Q: Addition to an alkyne is a,

a. three stage process

b. two stage process

c. single stage process

d. none of the above

Solution: The correct answer is option “b”. Addition to an alkyne is a

two-stage process alkyne ⇒ alkene ⇒ alkane

Covalent Bond

Covalent bond is a chemical bonding process in which pairs of

electrons are shared between two atoms. The force of attraction or

repulsion between two atoms, when they share electron pair or

bonding pairs, is called as Covalent Bonding. Carbon, having four

electrons in its outer shell has given it the ability to form innumerable

molecules and bonds. This is why carbon has so many elements and

allotropes. Confused as to why? It is because a carbon atom is in the

most favorable situation to form a covalent bond. Let us learn further.

What is a Covalent Bond?

Covalent bonding occurs between non-metal elements when pairs of

electrons are shared by atoms. Atoms will covalently bond with other

atoms to attain the nearest noble gas configuration. Here when

elements share their electrons, they do not become positive or

negative, since they are neither gaining or sacrificing compounds.

Thus no ions are formed by covalent bonding.

Let us learn about covalent bonding through examples given below

Covalent Bonding of Hydrogen Molecule

The simplest way to learn about covalent bond is the example of a

hydrogen molecule. Are you aware that hydrogen that is present in our

atmosphere cannot exist in its original form? It has to bond with

another atom, for it to be stable enough. This is why the molecular

formula of hydrogen is always H2.

A single atom of Hydrogen has one electron, i.e. its atomic number 1.

It has its only electron in its first and only orbit. Now to be a stable

molecule it needs to complete its duplet state. So a single hydrogen

atom will remain unstable unit it attains one more electron. So we can

say the valency of hydrogen is 1. The valency of an atom depends on

its sharing capacity. So the hydrogen atom shares its single atom with

another hydrogen atom. Now both hydrogen atoms have two (shared)

electrons in its outer shell and it is a stable molecule H2. This bond

formed by sharing electrons is nothing but a covalent bond.

Covalent Bonding of Carbon Compounds

Covalent carbon compounds are those where there is a carbon-carbon

bond. These covalent compounds have stronger bonds than other

compounds. This is because carbon is a small atom. Its nucleus has a

strong force of attraction and holds these bonds tightly together. So

covalent carbon compounds have a strong bond between themselves.

Now let us understand why the covalent bonding is so relevant for

carbon atoms.

As you are aware the reactivity of elements is its ability to lose or gain

electrons from so that its outermost shell has a complete octet (or

duplet in case of hydrogen) namely attain noble gas configuration.

However, carbon has a unique situation. It has four electrons in its

outermost shell, so one of the following situations must happen.

Situations ● It can loose the four electrons in its last shell and become a

cation i.e. C4+. However to lose all four of these electrons

would require a large amount of energy, and the resulting atom

would be unstable with six neutrons holding only two electrons

in one shell.

● The other option a carbon atom has is to obviously gain four

electrons from another atom. But it would be extremely

difficult for the resulting carbon atom to be stable. Ten

electrons will have to be held by six neutrons in the nucleus.

So instead, carbon comes up with a unique solution. It shares its

valence electrons with those of other carbon atoms, or even atoms of

other elements. Now these shared atoms of the last shell, belong to

both the atoms, hence forming a bond between these atoms. Now both

atoms have a complete outer shell with eight atoms and have both

attained noble gas configuration. This sharing of atoms, instead of

gaining or losing is called covalent bonding. And Carbon, since its

atomic number is 6, and it has four electrons in the last shell has the

most favourable structure for covalent bonding.

Some Important Carbon Compounds with Covalent Bonds

Methane: Now let us take a look at covalent bonding in some carbon

elements. Let’s get started with that of Methane. Its chemical formula

is CH4. Now that means one atom of carbon combines with four atoms

of Hydrogen to make one molecule of methane. All the hydrogen

atoms have only one electron in their outermost shell and carbon has

four. So carbon shares each of its four electrons with one atom of

carbon. This way carbon now has a complete octet and all four

hydrogen atoms have a complete duplet.

Carbon dioxide: Let us take a look at another element you should be

very familiar with, carbon dioxide. Here two atoms of oxygen

combine with one atom of carbon thus giving us the molecule CO2. As

we already know now that carbon has four electrons in its outer shell,

whereas oxygen with atomic number 8, has six atoms in the last shell.

So carbon shares two of its atoms with each atom of oxygen. This way

all three atoms complete their octet giving us one stable molecule.

Solved Example for You

Q: Which one of the following contains ionic, covalent and coordinate

bonds?

a. NaOH

b. NaCl

c. NaCN

d. NaNC

Sol: The correct answer is option ‘d’. NaNC contains ionic, covalent

and coordinate bonds. An ionic bond is present in Na+ ion and –NC

ion. A covalent bond is present between C and N atoms. Coordinate

bond is also present between C and N atoms.