1. Bonding in Carbon

Bonding in Carbon: The Covalent bond, Electron dot structure, Physical properties of organic compounds, Allotropes of Carbon.

Hard Water

Hard water contains salts of calcium and magnesium, principally as bicarbonates, chlorides, and sulphates. When soap is added to hard water, calcium and magnesium ions of hard water react with soap forming insoluble curdy white precipitates of calcium and magnesium salts of fatty acids.

2C17H35COONa+MgCl2 → (C17H35COO)2Mg+2NaCl

2C17H35COONa+CaCl2 → (C17H35COO)2Ca+2NaCl

These precipitates stick to the fabric being washed and hence, interfere with the cleaning ability of the soap. Therefore, a lot of soap is wasted if the water is hard.

Covalent Bonds

Difficulty of Carbon to Form a Stable Ion

To achieve the electronic configuration of the nearest noble gas, He, if the carbon atom loses four of its valence electrons, a huge amount of energy is involved. C4+ ion hence formed will be highly unstable due to the presence of six protons and two electrons.

If the carbon atom gains four electrons to achieve the nearest electronic configuration of the noble gas, Ne, C4− ion will be formed. But again, a huge amount of energy is required. Moreover, in C4+ ion it is difficult for 6 protons to hold 10 electrons. Hence, to satisfy its tetravalency, carbon shares all four of its valence electrons and forms covalent bonds.

Ionic Bond

Ionic bonding involves the transfer of valence electron/s, primarily between a metal and a nonmetal. The electrostatic attractions between the oppositely charged ions hold the compound together.

Ionic compounds:

Are usually crystalline solids (made of ions)

Have high melting and boiling points

Conduct electricity when melted

Are mostly soluble in water and polar solvents

Covalent Bond

A covalent bond is formed when pairs of electrons are shared between two atoms. It is primarily formed between two same nonmetallic atoms or between nonmetallic atoms with similar electronegativity.

Lewis Dot Structure

Lewis structures are also known as Lewis dot structures or electron dot structures.

These are basically diagrams with the element’s symbol in the centre. The dots around it represent the valence electrons of the element.

Lewis structures of elements with atomic number 5-8

Covalent Bonding in H2, N2 and O2

Formation of a single bond in a hydrogen molecule:

Each hydrogen atom has a single electron in the valence shell. It requires one more to acquire the nearest noble gas configuration (He).

Therefore, both the atoms share one electron each and form a single bond.

 

 Formation of a double bond in an oxygen molecule:

Each oxygen atom has six electrons in the valence shell (2, 6). It requires two electrons to acquire the nearest noble gas configuration (Ne).

Therefore, both the atoms share two electrons each and form a double bond.

Formation of a triple bond in a nitrogen molecule:

Each nitrogen atom has five electrons in the valence shell (2, 5). It requires three electrons to acquire the nearest noble gas configuration (Ne).

Therefore, both atoms share three electrons each and form a triple bond.

Single, Double and Triple Bonds and Their Strengths

A single bond is formed between two atoms when two electrons are shared between them

A double bond is formed between two atoms when four electrons are shared between them, i.e., one pair of electrons from each participating atom. It is depicted by double lines between the two atoms.

A triple bond is formed between two atoms when six electrons are shared between them, i.e., two pairs of electrons from each participating atom. It is depicted by triple lines between the two atoms.

Bond strength:

  The bond strength of a bond is determined by the amount of energy required to break a bond.

This is to signify that the energy required to break three bonds is higher than that for two bonds or a single bond.

Bond length:

Bond length is determined by the distance between nuclei of the two atoms in a bond.

The order of bond length for multiple bonds is: Triple bond<double bond<single bond

The distance between the nuclei of two atoms is least when they are triple bonded.

Covalent Bonding of N, O with H and Polarity

In ammonia (NH3), the three hydrogen atoms share one electron each with the nitrogen atom and form three covalent bonds.

1.Ammonia has one lone pair.

2.This causes the N atom to acquire a slight negative charge and H atom a slight positive charge

3.All three N-H covalent bonds are polar in nature.N atom is more electronegative than

​the H atom. Thus, the shared pair of electrons lies more towards N atom.

 

In water (H2O), the two hydrogen atoms share one electron each with the oxygen atom and form two covalent bonds.

 Covalent Bonding in Carbon

A methane molecule (CH4) is formed when four electrons of carbon are shared with four hydrogen atoms as shown below.

Diamond

Diamond has a regular tetrahedral geometry. This is because each carbon is connected to four neighbouring carbon atoms via single covalent bonds, resulting in a single unit of a crystal. These crystal units lie in different planes and are connected to each other,  resulting in a rigid three-dimensional cubic pattern of the diamond.

Diamond:

1.Has a high density of 3.5g/cc.

2.Has a very high refractive index of 2.5.

3.Is a good conductor of heat.

4.Is a poor conductor of electricity.

Graphite

In graphite, each carbon atom is bonded covalently to three other carbon atoms, leaving each carbon atom with one free valency. This arrangement results in hexagonal rings in a single plane and such rings are stacked over each other through weak Van der Waals forces.

Graphite:

1.Has a density of 2.25 g/cc.

2.Has a soft and slippery feel.

3.Is a good conductor of electricity.

C60

C60, also known as Buckminsterfullerene, is the very popular and stable form of the known fullerenes. It is the most common naturally occurring fullerene and can be found in small quantities in soot. It consists of 60 carbon atoms arranged in 12 pentagons and 20 hexagons, like in a soccer ball.

CHAPTER - 4

COMPOUND AND ITS CARBON

Carbon:-  (i)Most carbon compounds are poor conductors of electricity. Therefore, the bonding in these componds does not give rise to any ions

1. They have low melting and boiling points as compared to ionic compounds
2. Forces of attraction between the molecules are not very strong.
3. The atomic number of carbonis
4. It has four elements I its outermost shell and needs to gain or lose four electrons to attain noble gas configuration.

If carbon were to gain lose electrons:-

• It  could gain four electrons forming C^4-  anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons.
• It could lose four electrons forming C⁴⁺ cation. But it would require a large amount of energy to remove electrons. Carbon overcomes this problem by sharing its valences electrons with other of carbon or with atoms of other elements.

 Bonding in carbon

 Carbon form covalent bounds.  

• Covalent bound formation involves sharing of electrons between bonding atoms which may be either same or different.
• The number of lectrons contributed by an atom for sharing is known as its covalency.

       For example 

1. Molecule of hydrogen  

   

2. Molecule of oxygen

3. Molecule of Nitrogen

4. Structure of methane

Methane CH₄  is widely used as a fixed and is a major component of bio-gas and compressed natural gas ( CNG) .

• CHARACTERISTICS OF COVALENT COMPOUND :-

1. These compounds are molecula in nature  i.e. , they exist as single molecules)
2. These are insoluble in water and soluble in benzene , kerosence and petrol etc.
3. These compounds are poor conductor of electricity.

Allotropes of carbon

  The property due to which an element exists intwo or more forms, which differ in their physical and chemical properties is known as ‘Allotropes’ and the various forms are called “Allotropes”.

• carbon exists in two allotropic  form
• (i) crystalline                 (ii)  amorphous.

The crystalline forms are diamond and graphite the amorphous forms are coat , characol etc.

• In diamound , each carbon is bonded to for other carbon atoms forming rigid 3-D dtructure. Diamond is the nardest substance. * in graphite each carbon is bonded to three other carbon atom. Graphite structure is formed by the hexagonal arrays. Graphite is smooth and slippery . it is very good conductor of electricity.
• Fullerenes form another class of carbon allotropes. The first one to be identified was C-60, which has carbon atoms arranged in the shape of a football.