Carbon and Its Compounds

Covalent Bonds

As I have written before , the bond made from the sharing of electrons between atoms in their outermost shell is called a covalent bond.

Properties of Covalently Bonded Molecules

There are some properties associated with covalently bonded molecules:

1. Strong bonds between molecules

2. Weak intermolecular forces. Due to which they also have:

   • Low melting point and boiling point

3. Covalent bonding does not result in the formation of ions, thus they are not good conductors of electricity.

Allotropes

When an element can can have several structural forms while being in the same physical state, is called allotropy.

And these forms are called allotrope of the element. There are two types of carbon allotropes:

1. Crystalline

2. Amorphous.

Crystalline Form

Diamond

• Physical properties

  • Hardest natural substance known
  • Colorless and transparent
  • Very bright shine
  • High-meriting point (About 3500°C)
  • Non-conductor of electricity

• Chemical properties.

  • When diamond is burnt in the presence of oxygen, only carbon dioxide is formed, with nothing else left behind, thus diamond is only made up of carbon.

  • Therefore, its symbol is also the same as carbon, i.e, ‘C’.

• Structure

• Each carbon atom is bonded to 4 carbon atoms in a 3 dimensional rigid structure.

• There are 4 carbon atoms at the vertices of a regular tetrahedron.

• It doesn’t conduct electricity because all 4 valence electrons of carbon atoms are used in covalent bonds with 4 other carbon atoms, leaving no free electrons.

• Uses

  • Cutting glass and drilling rocks
  • Jewellery making because of its great ability to reflect and refract light
  • used by eye surgeons as a tool to remove cataract.

Graphite

1. Physical properties

   • Graphite is a greyish black substance.
   • It’s smooth and slippery.
   • It’s a good conductor of electricity.
   • It has a high melting.

2. Chemical properties.

   • If burnt in the presence of oxygen, it only leaves carbon dioxide behind. Therefore, it can be assumed that graphite is made up of only carbon. Its symbol is C.

3. Structure

• Each carbon atom is bonded to 3 other carbon atoms and they form hexagonal rings.

• These hexagonal rings exist in multiple layers, over each other.

• Each hexagonal ring layer is held together by weak Van der Waals forces.

• Thus, each layer can easily slip over each other, making graphite soft, and good for lubrication.

• It’s a good conductor of electricity because each carbon atom is only bonded to 3 other carbon atoms leaving one electron free.

Buckminsterfullerene

• Named after American architect Buckminster Fuller, because he invented the geodesic dome which is similar to the structure of C₆₀ .

• One molecule consists of 20 hexagonal and 12 pentagonal rings of carbon atoms.

• Used as lubricant, semi-conductor, superconductor.

Catenation

• The unique property of carbon to form bonds with other carbon atoms resulting in long chains of such molecules is called catenation. The extent to which carbon can perform catenation is unseen in other elements.

• Silicon can form compounds with hydrogen or oxygen for upto 7 or 8 atoms, but these are very reactive and they therefore are not useful.

• On the other hand, carbons can form very strong, long, and stable bonds. This gives us many long compounds.

Tetravalency

It’s pretty simple, ’tetra’ means 4, thereofre tetra + valency = Tetravalency.

• Carbon is capable of bonding with 4 other atoms of carbon or some other mono valent element, like hydrogen.

• Carbon bonds are exceptionally stable because carbon atoms are very small.

Bonds & Structure

1. Bonds

There are three kinds of chemical bonds, namely:

• Single Bond, i.e., the sharing of 1 pair of electrons.

• Double Bond, i.e., the sharing of 2 pair of electrons.

• Triple Bond, i.e., the sharing of 3 pair of electrons.

There are three types of bonds:

To make a simple compound, say, CH₄ , we have to make sure a carbon atom has single bonds with 4 other hydrogen atoms.

Like this:

In the picture above, carbon has a single bond with each hydrogen atom, i.e., it shares one electron with each hydrogen atom.

Isomerism

Compounds having the same molecular formula with different structure are called structural isomers. This phenomena is known as isomerism. Carbon compounds are especially good at forming isomers.

Since the same molecular formula can result in different types of compounds, there is a system of nomenclature designed to name carbon compounds. We’ll look into that later.

Saturated & Unsaturated Compounds

Carbon compounds which only contain carbon and hydrogen are called hydrocarbons.

Saturated Compounds

Compounds in which there are only single bonds between carbon atoms are called saturated compounds.

• These are also called alkanes (-).

For example, Methane.

Unsaturated Compounds

Compounds in which there are multiple (double or triple) bonds between carbon atoms are called unsaturated compounds.

• These are also called alkene (=) and alkynes (≡).

For example, Propylene or Propene.

General Formulae of Hydrocarbons

1. Alkane

General Formula: C_nH_2n+2 .

2. Alkene

General Formula: C_nH_2n .

3. Alkyne

General Formula: C_nH_2n-2 .

Functional Groups

A group of atoms in a hydrocarbon which imparts specific chemical properties, is called a functional group.

It’s called so because it changes the functionality of the compound.

Functional groups are a group heteroatoms, i.e., any atoms other than carbon or hydrogen in a hydrocarbon.

Homologous Series

Homologous series is a series of hydrocarbon compounds with similar chemical properties and some functional groups, differing from the successive member of the series by one methylene group, i.e, CH₂ .

It should be noted that in the diagram above, the physical properties of the elements change because the size of carbon chain changes. However, the chemical properties remain the same since the functional group remains the same.

Nomenclature

As we know, isomerism can make it so the same molecular formula results in different kinds of susbtances. Therefore, we need a system to name these substances that gives us an idea about them.

These guidelines were framed and are maintained by International Union of Pure and Applied Chemistry (IUPAC)

First, let’s look at the table of stuff we are going to need.

* These are alkyl groups, i.e, a group derived from alkanes by removal of a hydrogen atom from any carbon atom.

** This is an indicator of the number of carbon atoms in the main chain, of the compound. From Meth (1) to Dec (10)

Writing Formula

Position of Substitute + Name of Substitute + Wordroot + Position of Double-Bond or Triple-Bond + ane/ene/yne + Position of functional group + Suffix of functional group.

Rules of Nomenclature

1. Longest Chain Rule

First of all, the longest carbon chain is identified. There is a priority system in numbering chains.

2. Lowest Numebr Rule

Number the longest chain such that, the branched carbon atoms / substituents get the lowest possible number.

• If the chain has a double or triple bond, then the the carbon atoms involved in this bond should get priority over branches and should be given the lowest number possible.

• If there is a functional group in present in the carbon chain, then the longest chain containing the functional group should be numbered in a such a way that they get the lowest number possible.

Thus, here we have a priority list:

Functional Group > Double/Triple Bond > Branched Carbon Atoms / Substituents

3. Use of Prefixes

If the longest chain contains more than one substituent of the same kind then their positions, after numbering, are written separately and a prefix according to their number is attached to that substituent’s name, such as di, tri etc.

Say you have 2 Methyl groups at 2 and one at 3, like here:

Now, how are we supposed to name this? Let’s go back to the writing system I mentioned previously. First, the positions of the substituents is 2,2,3. Yes, if the same (or not) and more than one substituents are present at the same spot, they both get a number each like 2,2.

Now, the name of all the substituents is Methyl. The word root will be ‘Pent’ since the main chain has 5 carbon atoms. There are no functional groups or multiple bonds here, so we can skip things related to them. Now we add ‘ane’ suffix since all the carbon atoms have a single bond. Thus, we have the name:

2,2,3-Trimethylpentane

That ‘Tri’ is because we have 3 of the same thing (Methyl group in this case). Similarly, it could have been ‘Di’ if we had 2 Methyl groups only and so on.

Note: Numbers are separated by commas (,) and letters and number are separated by dashes (-).

4. Arrange Prefixes Alphabetically

The substituents prefixes such as ‘Methyl’ and ‘Propyl’ must come in alphabetical order, irrespective of the numerical value of their positions.

For example, if we have a compound with a methyl group at 2 and an ethyl group at 3 such as here:

The name will be 3-Ethyl-2-Methylpentane and NOT 2-Methyl-3-Ethylpentane even though 2 is less than 3 and you might think, should come first.

5. Same Positions Rule

Give the lowest number to the alphabetically first substituent if more than one of them is present and left to right and right to left numbering yield the same array of positions.

Again, here’s an example:

Here, both the the Left -> Right and Left <- Right numbering yields the same positions, namely 3,4.

The only difference is the substituents, they can be either :

• 3-Ethyl and 4-Methyl

or they can be:

• 3-Methyl and 4-Ethyl

The rule says the correct answer to that question is the first pair, i.e, 3-Ethyl and 4-Methyl because alphabetically Ethyl comes first. And thus, the name of this compound will be :

• Position of substituents : 3,4
• Name of substituents: Ethyl, Methyl
• Wordroot: Hex (6 Carbons)
• Suffix : Ane (because only single bonds are present)

3-Ethyl-4-Methylhexane

Functional Groups : Ketone vs. Aldehyde

Since we put the suffixes of functional groups at the end of the compound name, for example, ‘-ol’, it’s important to know which functional groups has what suffix.

Generally, at this level you only get a few functional groups, like alcohol, aldehyde etc. One pair of functional groups, namely ketone and aldehyde are kind of confusing since they have very similar structures. They both contain a carbonyl functional group, i.e., C=O.

However, it’s very easy to distinguish them:

Aldehyde

If at least one of the atoms bonded to the carbon atom in carbonyl functional group (C=O), is a hydrogen atom then it’s an aldehyde. Aldehydes have the suffix ’-al’.

For example:

As can be seen from the structure, an aldehyde group has to come at the end of a carbon chain.

Ketone

If both of the atoms of bonded to the carbon in the C=O group are not hydrogen, then it’s a ketone. Ketones have the suffix ’-one’

Unlike aldehydes, ketones can come anywhere in the chain, as shown here:

Combustion

The process of burning of a carbon compound in air to give carbon dioxide heat and light is known as combustion. Simply it’s just burning.

Alkanes produce a lot of heat, thus they are excellent fuels.

• Methane is a natural gas and it produces a lot of heat, therefore its used as fuel in homes, transport and industry.

• The LPG cylinder contains butane.

• Carbon compounds are used as fuel because they release a lot of heat.

Combustion in Saturated & Unsaturated Compounds

• Saturated hydrocarbons burned completely giving a blue flame, given they have enough oxygen, but if they don’t get sufficient oxygen they have incomplete combustion and give yellow, sooty, flame,

• Unsaturated hydrocarbons, on the other hand, give yellow, sooty flame irrespective of the amount of oxygen.

Flames

Flames on things like burning wood are produced because volatile substances on it vaporize giving it a flame. It’s is only produced when gaseous substances burn.

That’s why things like charcoal don’t produce a flame because they don’t have any volatile or gaseous substance.

Oxidization

Addition of O₂ or removal of hydrogen is called oxidization.

• Oxidizing Agent: Compound capable of adding oxygen to others.

Example: Alkaline Potassium Permanganate ( KMnO₄ ) or acidified Potassium dichromate ( K₂Cr₂O₇ ).

Oxidization in Alcohols

On oxidization, alcohols turn into their corresponding acid.

As seen in the diagram above, the carbon with the functional group OH, loses its hydrogen and that causes it to forms a double bond with an oxygen atom, resulting in the corresponding alcohol.

Addition Reaction

In addition reactions unsaturated compounds react with a molecule such as H₂ , Cl₂ , Br₂ etc. to give saturated hydrocarbon compounds as products.

• Addition reactions are a characteristic property of unsaturated hydrocarbons, i.e., of alkenes and alkynes.

Specifically, the type of addition reaction we are intrested in is hydrogenation.

Hydrogenation

Catalytic hydrogenation is a form of addition reaction in which hydrogen is added in the presence of a catalyst such as nickel.

Hydrogenation of Oils

The process of hydrogenation reaction is commonly used to produce “vegetable ghee.” Which is just hydrogenated vegetable oil.

The reaction used for this purpose typically goes like this:

Vegetable oils containing unsaturated fatty acids are good for health. Hydrogenation produces saturated trans fats in these vegetable oils which have been linked to multiple heart diseases, causes obesity and is overall bad for health.

The Bromine Water Test

A solution of bromine in water is called bromine water. It is red-brown in color because of the presence of bromine. If an organic compound manages to de-colorize bromine water then it is unsaturated.

Saturated compounds don’t de-colorize bromine water. This happens because, when bromine water is added to an unsaturated organic compound, the Br element in the solution reacts with the unsaturated organic compound and leaves the solvent, resulting the the solution losing its color. Since bromine can’t perform the same reaction with saturated organic compounds, they don’t de-colorize the solution.

Substitution Reaction

Substitution reactions are sort of the addition reactions of alkanes, in the sense of being their characteristic property. Since saturated hydrocarbons have all their carbon atoms engaging in some kind of bond (that’s why they are called saturated ) they are generally pretty unreactive and stable. But they do take part in one specific type of reaction.

The reaction in which one or more hydrogen atoms of a saturated hydrocarbon is replaced by some other atoms.

• Substitution reactions are a characteristic property of saturated hydrocarbons, i.e., of alkanes.

• Substitution reaction involving chlorine is called chlorination. This happens in the presence of sunlight. A substitution reaction with methane makes chloromethane.

Important Compounds

Ethanol

Ethanol, chemically C₂H₅OH , is a widely used substance in organic chemistry.

• Physical properties.

  • It’s a colorless liquid.
  • It has a pleasant smell.
  • The boiling point is 351K (78°C).
  • It’s miscible with water.
  • It has no ions, therefore it’s a non-conductor of electricity.

• Chemical properties

  • Oxidization by oxidant agents. As displayed here

  • Reaction with sodium: Ethanol reacts with sodium leading to the evolution of hydrogen gas.

  • Reaction to give ethene : Heating ethanol at 443K with excess concentrated sulphuric acid results in the dehydration of ethanol to give ethene. The concentrated sulphuric acid can be regarded as a dehydrating agent as it removes water from ethanol.

• Uses of Ethanol

  1. It’s used in the manufacture of paints, medicines, dyes, perfumes, soap, and synthetic rubber.

  2. Ethanol is the active ingredient of beverages like wine, beer, whiskey and other liquors.

  3. It’s used an antiseptic to sterilize wounds and syringes.

  4. It’s used as antifreeze in the radiators of vehicles in cold countries.

  5. It’s used in medicines such as cough syrup etc.

• Terms Related to Ethanol

  1. Rectified Spirit: Ethanol containing 5% water.

  2. Absolute Alcohol: 100% pure ethanol.

  3. Denatured Alcohol: Ethanol with poisonous substances, such as Methanol, to prevent drinking.

• Effects of Ethanol on The Human Body

The consumption of large quantities of ethanol results in:

• The slowing down of metabolic processes,
• Suppression of the nervous system.
• Lack of coordination
• Mental confusion, drowsiness.
• Lowering of consciousness and eventually being completely unconscious.

It gives a sense of relaxation, but it seriously impairs:

• Sense of judgment
• Sense of timing
• Muscular coordination

As mentioned previously, to stop the drinking of industrially produced ethanol, various poisonous substances are mixed in with it, like methanol which can quickly kill a human being. This is called denatured alcohol.

• It causes addiction
• It damages liver if taken regularly in large amounts.

Ethanoic Acid

Commonly called acetic acid, ethanoic acid, chemically CH₃COOH , is another important substance borne out of organic chemistry.

• Physical Properties

  • 5%-8% of solution in water is vinegar.

  • Used for preserving food.

  • Boiling point of pure ethanoic acid is 290K (17°C). Therefore, it’s also called ‘glacial acetic acid’.

• Chemical Properties

  • Esterification Reaction: Ethanoic acid reacts with ethanol in the presence of an acid catalyst to give an ester. This process is called esterification.

  • Saponification Reaction: Esters are further treated with NaOH solution get converted back to alcohol and salt of carboxylic acid. This is also used for making soaps.

  • Acid base reaction is just as usual. It gives salt and water.

  • Just like other acids, ethanoic acid’s reaction with carbonates or hydrogencarbonates gives a salt, carbon dioxide and water.

Soaps

A soap is a sodium or potassium salt of long chain carboxylic acid, also known as fatty acids, having cleansing properties in water.

Example: Sodium stearate (C₁₇H₃₅COONa) , Sodium palmitate (C₁₅H₃₁COONa)

Making Soap

Soap is prepared by heating animal fat or vegetable oils with NaOH solution. They react with NaOH to produce soap and glycerol which is a sweetener.

Structure of Soap

Soaps are made of a hydrophilic head, i.e., a head that likes water and a hydrophobic tail, i.e., a head that dislikes water. In the formula RCOONa, the R is the long tail and the Na is the head.

How Do Soaps Clean?

If you look closely, the structure of one molecule of soap looks like a sperm! That’s because this is a common structure used on the molecular level for movement.

The tail dislikes water and therefore tries to avoid it. But it’s also oil soluble, so it’s attracted to oil. The head likes water and it tries to interact with water as much as possible.

When a cloth is washed, the fats and oils in it are surrounded by soap molecules in a specific structure called ‘micelle’, due the behaviour of the molecule’s head and tail.

As can be seen, the tail arrange itself towards the oil molecule and the head positions itself towards the water, thus they sort of trap oil, dirt etc. When the cloth is scrubbed in the soap solution, the oil and other contaminants entrapped by the micelle get dispersed, leaving the cloth clean and the solution dirty.

Soaps in Hard Water

Hard water contains calcium and magnesium salts, that’s what gives them the name. When soap is mixed with hard water, Ca²⁺ and Mg²⁺ in the hard water react with soap to form insoluble calcium and magnesium salts of fatty acids.

Basically,

C₁₇H₃₅COONa + MgCl₂ ⟶ (C₁₇H₃₅COO)₂Mg

It can obviously also happen with calcium,

C₁₇H₃₅COONa + CaCl₂ ⟶ (C₁₇H₃₅COO)₂Ca

This product at the end is formed as a white precipitate called scum. Thus, soap is ineffective in hard water.

Detergents

Detergents are known as ‘soapless soaps.’

These are sodium salts of long chain benzene sulphonic acid or sodium salt of a long chain alkyl hydrogen sulphate.

Example: C₁₇H₃₅SO₃Na

Detergents in Hard Water

Detergents simply do not react with calcium and magnesium salts present in hard water to form insoluble precipitate in the form of scum. Thus, detergents remain effective in hard water.