Carbon and Its Compounds

• Carbon is a versatile element.

• In earth’s crust, carbon is 0.02% and found in form of minerals.

• Atmosphere has 0.03% of Carbon dioxide.

• All living structures are carbon based.

Types of Bond

1. Ionic Bond

When there is transfer of electrons between atoms ionic bond is formed.

Example NaCl

In this Na lose its one electron and chlorine gain the one elecron to attain a noble gas configuration.

The atom which gain the electron acquires -ve charge and the atom lose the electron acquires +ve charge.

2. Covalent Bond

When there is sharing of electrons between the atoms of same or different kind the covalent bond is formed.

Types of covalent bond

(i) Single Bond

The bond which is formed between the atoms and only a pair of electrons are involve in it to attain a noble gas configuration.

Example H2

(ii) Double Bond

The bond which is formed between the atoms and only a 2pair of electrons are involve in it to attain a noble gas configuration.

Example O2

(iii) Triple Bond

The bond which is formed between the atoms and only a 3pair of electrons are involve in it to attain a noble gas configuration.

Example N2

⇒ Allotropes of carbon

1. Diamond
2. Graphite
3. Buckminsterfullerene
1. Diamond

• It is the hardest material.

• It is a bad conductor of electricity because it has no free electron .

• Used in ornamentals and cutting blades.

2. Graphite

• It is soft and soapy in touch.

• It is a good conductor of electricity because it has one free electron .

• It is used in pencil etc.

3. Buckminsterfullerene

• It is combination of C-60 atoms.

• Football shape

Covalent Bond in Carbon

The atomic number of carbon is 6 and its electronic configuration is 2,4. To attain a noble gas configuration it can

1. Gain 4 electrons. But it would be difficult for nucleus to hold 4 extra electrons.

2. Lose 4 electrons. But it would require a large amount of energy to remove 4 electrons.

• It is difficult thus for an atom of carbon to either gain or lose electrons.

• Carbon attains the noble gas configuration by sharing its valence electrons with other atoms. Atoms of other elements like hydrogen,oxygen, nitrogen, chlorine also show sharing of valence electrons.

• It is evident that the number of shared pair of electrons can be one, two or three. Try making the structures of H2O and CH4.

• Bond formed by the sharing of an electron pair between two atoms is called covalent bond.

• Covalently bonded molecules have low melting and boiling points because of comparatively weaker intermolecular forces, unlike ionic compounds.

• These molecules are generally poor conductor of electricity since no charged particles are formed.

Versatile Nature of Carbon Atoms

Two important properties of carbon atom enable carbon to form enormously large number of compounds.

⇒ Catenation

Property of carbon atom to form bond with other atoms of carbon is called catenation. Like carbon, silicon forms compounds with hydrogen up to seven or eight atoms of silicon.

⇒ Tetravalency

Having a valency of 4, carbon atom is capable of bonding with atoms of oxygen,hydrogen,nitrogen,sulphur,chlorine and other elements. The smaller size of carbon atom enables nucleus to hold the shared pair of electrons strongly, thus carbon compounds are very stable in general.

Saturated and Unsaturated Carbon Compounds

Saturated Hydrocarbons

Have single bond between carbon atoms referred as alkanes and are less reactive.

• Alkane : CnH2n+2

Unsaturated Hydrocarbons

Have double or triple bond between carbon atoms referred as alkenes and alkynes

• Alkene : CnH2n

• Alkyene : CnH2n–2

Formulae and Structures of Saturated Compounds of Carbon and Hydrogen

1. Methane CH4

2. Ethane C2H6

3. Propane C3H8

4. Butane C4H10

5. Pentane C5H12

6. Hexane C6H14

7. Septane C7H16

8. Octane C8H18

Structural isomers

These are the compounds having identical molecular formula but different structures.

Heteroatom and Functional Group

• In hydrocarbon chain, one or more hydrogen atoms can be replaced by other atoms in accordance with their valencies. The element that replaces hydrogen is called a heteroatom.

• These heteroatoms and the group containing them impart chemical properties to the compound and hence are called functional groups.

Homologous Series

• It is a series of compounds in which the same functional group substitutes for hydrogen in a Carbon chain.

• For instance, The ALCOHOLSs: CH3-OH, C2H5-OH, C3H7-OH, C4H9-OH.

• The successive member differs by –CH2-; unit and 14 units of mass.

• The chemical properties are imparted by the functional group thus all members have similar chemical properties. But the members have different physical properties.

• The physical properties vary among the members of homologous series due to difference in their molecular mass.

• Melting point and boiling point increases with increasing molecular mass.

Nomenclature of Carbon Compounds

1. Identify the number of carbon atoms in the compound and chose the longest chain of carbon atom.

2. Functional group is indicated either by prefix or suffix.

FunctionalGroup             Suffix                      Prefix

Alkene                                  ene
Alkyne                                  yne
Alcohol                                   ol
Aldehyde                                al
Ketone                                   one
Carboxylicacid              oic acid
chlorine                                                               chloro

3. If a suffix is added, then final ‘e’ is removed from the name

eg. methanol (methane-e = methan + ol).

⇒ Chemical properties of Carbon compounds

1. COMBUSTION

• Carbon compounds generally burn(oxidize) in air to produce carbondioxide and water, and release heat and light energy.

CH4 + O2 → CO2 + H2O + heat and light

• Saturated hydrocarbon burns generally with a blue flame in good supply or air and with a yellow sooty flame in limited supply of air.

• Sooty flame is seen when unsaturated hydrocarbons are burnt.

• Burning of coal and petroleum emits oxides of sulphur and nitrogen which are responsible for acid rain.

2. OXIDATION

• Alcohols can be converted to carboxylic acids by oxidizing them using alkaline potassium permanganate or acidified poatassium dichromate (they add oxygen to the reactant,thus are called oxidizingagents).

3. ADDITION REACTION

Hydrogen is added to unsaturated hydrocarbon in presence of palladium or nickel as catalyst.

4. SUBSTITUTION REACTION

In saturated hydrocarbons, the hydrogen attached to carbon can be replaced by another atom or group of atoms in presence of sunlight.

Esterification

Carboxylic acids react with alcohols in presence of few drops of concentrated sulphuric acid as catalyst and form sweet smelling compounds called ester.

Hydrolysis:

On heating with an acid or a base the ester forms back the original alcohol and carboxylicacid.

CH3COO CH2CH3 + NaOH → CH3COONa + CH3-CH2OH
CH3COO CH2CH3 → 2 4 Dil.H SO HEAT
CH3COOH + CH3-CH2OH

• Alkaline hydrolysis of esteris also called saponification.

Soaps and Detergents

• Soap is sodium and potassium salt of carboxylic acids with long chain.

• Soaps are effective with soft water only and ineffective with hard water.

• Detergents are ammonium or sulphonate salts of carboxylicacids with long chain. They are effective with both soft as well as hard water. An ionic part (hydrophilic) and a long hydrocarbon chain (hydrophobic) part constitutes the soap molecule.

Structure of a Soap Molecule Cleansing Action of Soaps :

• Most dirt is oily in nature and the hydrophobic end attaches itself with dirt, while the ionic end is surrounded with molecules of water. This result in formation of a radial structure called micelles.

• An emulsion is thus formed by soap molecule. The cloth needs to be mechanically agitated to remove the dirt particles from the cloth.

• Scum is the magnesium and calcium salts present in hard water reacts with soap molecule to form insoluble products called scum, thus obstructing the cleansing action. Use of detergents overcome this problem as the detergent molecule prevents the formation of insoluble product and thus clothes get cleaned

NCERT EXERCISE

Question 1:

Provide the structures for the compounds provided below:

Butanone
Ethanoic Acid
Hexanal
Bromopentane

Question 2:

Name the following compounds:

Solution:

Hexane
Formaldehyde
Bromoethane

Question 3:
Give reason to why the reaction of ethanol to ethanoic acid is an oxidation reaction.

Solution:

As shown in the reaction: since oxygen is added in this reaction, the change from ethanol to ethanoic acid is known to be an oxidation reaction.

Question 4:

Why is the burnt mixture of oxygen and ethyne used for welding rather than that of ethyne and air?

Solution:

The production of heat is very important for welding metals. When oxygen and ethyne is burnt, it burns completely and produces a higher temperature than air and ethyne. Oxygen and ethyne produce very hot blue flame but the mixture of air and ethyne gives out a sooty flame which means that there are unburnt particles resulting in lesser heat.

Question 5:

What are oxidizing agents?

Solution:

When a substance gains electrons from a redox reaction whilst the oxidation number also reduces, it is known as an oxidizing agent.

Question 6:

Using bond formation of Methyl Chloride (CH3Cl), explain the basis of covalent bonding.

Solution:

Methyl chloride consists of:

One carbon atom
Three hydrogen atoms
One chlorine atom
Carbon atom, hydrogen atom, chlorine atom has four, one and seven valence electrons respectively where carbon shares four of its valence electrons with the three-hydrogen atoms and one chlorine atom. Therefore, it forms methyl chloride as shown in the chemical equation above.

In the dot structure, it can be seen that there are four shared electrons between carbon and the other atoms. In the reaction, each of the shared pairs are considered as one single covalent bond. Hence, methyl chloride is known to have four single covalent bonds.

Question 7:

Draw the electron dot structure for the following:

Ethanoic acid
H2S
Propanone
F2

Question 8:

Write down the meaning and explanation of homologous series.

Solution:

It is a series of compounds, which has the same functional group. This also contains similar general formula and chemical properties. Since there is change in the physical properties, we can say that there would be an increase in the molecular size and mass.

Question 9:

Using their physical and chemical properties, differentiate ethanol from ethanoic acid.

Solution:

Ethanol Ethanoic
Does not react with sodium hydrogencarbonate Bubbles and fizzes with hydrogencarbonate
A good smell Smells like vinegar
No action in litmus paper Blue litmus paper to red
Burning taste Sour taste

Question 10:

State the reason as to why there is micelle formation when soap is added to water.

Solution:

The reason for the micelle formation is because of the dirt particles in water and clean water. There are two mediums that are involved: one is pure water and the other being dirt (also called as impurities). The soap also has two mediums: (i) organic tail and (ii) ionic head. So the organic tail mixes and dissolves with the dirt whereas the oil or grease and ionic head dissolves and mixes with the water. Therefore, when the material to be cleaned is removed from the water, the dirt is taken off by the soap molecules in the water. Hence, the soap cleans by forming closed structures by mutual repulsion of the micelles (positively charged heads).

Question 11:

Explain why carbons and its compounds are used as fuels.

Solution:

Because, carbon and it’s compounds burn in air and also give out a lot of energy.

Question 12:

Why is scrum produced when hard water is treated with soap?

Solution:

Scrum is produced from hard water reacting with soap because a soap is wasted from reacting with calcium and the magnesium ions from the hard water. This wasted reaction then forms an insoluble precipitate that sticks as a white layer.

Question 13:

What will be the color change when soap is tested with red litmus paper?

Solution:

Soap is a base and it will turn red litmus paper to blue.

Question 14:

Define hydrogenation and write about its industrial application.

Solution:

Hydrogenation is a process or a chemical reaction between hydrogen and other compounds. It is usually done in presence of catalysts: for example nickel, palladium or platinum. Hydrogenation is used mainly to reduce or saturate organic compounds.

Question 15:

Provide a chemical test that could be used to differentiate between cooking oil and butter. Explain the steps to carry out the test.

Solution:

The test that could be used is bromine water test.

Steps:

Add little bromine water to cooking oil
In a different test tube, add bromine water to butter
If decolorizing happens, then it is considered an unsaturated compound and therefore, it is cooking oil. In addition, the test tube that does not decolorize is considered to be the saturated compound which is the butter.

Question 16:

Can you check if the water is hard using a detergent?

Solution:

That is not possible because of the formation of lather when detergent is mixed with water.

Question 17:

Why is beating or agitation necessary in order to get clean clothes?

Solution:

Clothes need to be beaten or agitated so that the soap micelles can trap the oil, grease or any other impurities that have to be removed. When they are being beaten or agitated, the particles are removed from the clothes’ surfaces and go into the water, thus cleaning the clothes.

Question 18:

Explain the process of cleansing action of a soap.

Solution:

There are so many impurities and dirt mixed in water, and most of all those dirt do not dissolve in the water. Soap molecules is a combination of salts such as sodium or potassium. The molecules are of long chain of carboxylic acids. So, when the carbon chain has dissolved in oil and ionic end has dissolved in the water, the soap starts cleansing and trapping the dirt. When this happens, the soap molecules forms structures that are called as micelles. One end of the micelle is used for capturing the oil droplets and then the other end being the ionic faces. This will then form an emulsion in water and help in dissolving the dirt or impurities when the clothes are washed.

The soap molecules have different properties at different ends. The first end being the hydrophilic end which dissolves in the water and is attracted towards the water and the second one being the hydrophobic end which is dissolved in the hydrocarbons and is repulsive to water. The hydrophobic tail aligns itself along the surface of water because it is not soluble in the water.