Chemical Bonding

Covalent
Reason — As compound X consists of molecules, it means that compound X is a covalent compound. Electrovalent compounds consist of ions. Hence, bonding in X is covalent.

Single covalent bond

Nitrogen
Reason — As the electronic configuration of N is [2,5] so when two nitrogen atoms come closer, each contributes three electrons and they have three shared pair of electrons between them. Therefore, it forms triple covalent bond [N ≡ N].

Lone pair of electrons are valence electrons that in a covalent bond are not shared with another atom.

Nitrogen has 5 electrons in its valence shell. In the formation of a nitrogen molecule, each nitrogen atom shares three electrons to complete its octet. Hence, 2 electrons in the outer shell of each nitrogen atom are not involved in bond formation. Formation of a nitrogen molecule from nitrogen atoms is shown in the diagram below:

Atomic orbit structure of carbon tetrachloride is shown below:

Type of bond present in carbon tetrachloride is Covalent Bond

(i) Sodium chloride — ionic bond.

(ii) Carbon tetrachloride — covalent bond.

(i) In covalent compounds, the bond is formed due to sharing of electrons.

(ii) A molecule of nitrogen contains a triple bond.

Methane consists of one carbon atom [2,4] and four hydrogen atoms [1]. Carbon needs four electrons to attain a stable electronic configuration of nearest noble gas - Ne, whereas, hydrogen needs one electron to attain stable electronic configuration of nearest noble gas - He.

Therefore, one atom of carbon shares four electron pairs one with each of the four hydrogen atoms, resulting in formation of methane molecule.

The atomic orbit structure diagram of the formation of methane molecule is shown below:

(a) An atom with electronic configuration 2, 8, 6 is Sulphur.

(b) A gaseous covalent molecule with four covalent bonds is Methane

The force which acts between two or more atoms to hold them together as a stable molecule is called a chemical bond and the concept is called chemical bonding.

Octet and duplet structures seem to represent stability and are said to be stable electronic configuration.

Noble gases have their outermost or valence shell complete i.e., they have 2 electrons in outermost shell e.g., helium [electronic configuration 2] or they have 8 electrons in outermost shell e.g., neon [electronic configuration 2,8] or argon [electronic configuration 2,8,8 ]. Hence, they have stable electronic configuration. They do not gain, lose or share electrons and are unreactive or inert.

Atoms of other elements have incomplete valence shell, hence they have unstable electronic configuration. So, they can gain, lose or share electrons to attain the stable electronic configuration of the nearest noble gas.

Atoms of elements other than noble gases, attain stable electronic configuration of the nearest noble gas by:

1. Transfer of valence electrons from a metallic atom to a non-metallic atom.
2. Mutual sharing of electrons between two pairs of atoms of non-metallic elements.

(a) The chemical bond formed between the two atoms by transfer of one or more electrons from the atom of a metallic element to an atom of a non-metallic element is called an electrovalent bond.

(b) The chemical compound formed as a result of transfer of one or more electrons from the atom of a metallic element to an atom of a non-metallic element is called an electrovalent compound. e.g., NaCl, CaO

(c) The chemical bond formed due to mutual sharing of electrons between the given pairs of atoms of non-metallic elements is called a covalent bond.

(d) The chemical compound formed due to mutual sharing of electrons between the given pair of non-metallic elements is called a covalent compound. e.g., Chlorine molecule, Oxygen molecule.

(a) Duplet Rule — For an atom to achieve stable electronic configuration it must have 2 electrons in the first shell [outermost] like that of noble gas Helium.

(b) Octet Rule — For an atom to achieve stable electronic configuration it must have 8 electrons in outermost orbit like that of noble gases other than Helium.

Atomic orbit structure diagram of the formation of sodium chloride by transfer of electrons from metallic sodium atom to non-metallic chlorine atom is shown below:

Calcium oxide is formed as a result of transfer of two valence electrons

• from metallic calcium atom ⁴⁰₂₀Ca; electronic configuration - 2,8,8,2 ; Nearest noble gas = Argon [2,8,8]
• to non-metallic oxygen atom ¹⁶₈O - electronic configuration - 2,6 ; Nearest noble gas = Neon [2,8]
• calcium loses two electrons - from its outer shell to attain stability of nearest noble gas - argon and becomes a calcium ion [cation] : Ca²⁺
• oxygen accepts two electrons - in outer shell to attain stability of nearest noble gas - neon and becomes an oxide ion [anion] : O^2-

Atomic orbit structure diagram of the formation of calcium oxide is shown below:

Calcium oxide is formed as a result of transfer of two valence electrons

• from metallic calcium atom ⁴⁰₂₀Ca; electronic configuration - 2,8,8,2 ; Nearest noble gas = Argon [2,8,8]
• to non-metallic oxygen atom ¹⁶₈O - electronic configuration - 2,6 ; Nearest noble gas = Neon [2,8]
• calcium loses two electrons - from its outer shell to attain stability of nearest noble gas - argon and becomes a calcium ion [cation] : Ca²⁺
• oxygen accepts two electrons - in outer shell to attain stability of nearest noble gas - neon and becomes an oxide ion [anion] : O^2-

Magnesium [At. no. 12 and electronic configuration 2,8,2] loses two electrons from it's outer shell in order to attain stability of nearest noble gas Neon [2,8] and becomes a magnesium ion [cation] : Mg²⁺.

Chlorine [At. no. 17 and electronic configuration 2,8,7] accepts one electron in it's outer shell to attain stability of nearest noble gas Argon [2,8,8] and becomes a chloride ion [anion] : Cl^1-.

Magnesium atom donates two electrons, whereas chlorine accepts one electron to give - chloride ion. Therefore, to accept the other electron donated by magnesium atom there must be another chlorine atom. Thus, one magnesium atom combines with two chlorine atoms to give MgCl₂

Hydrogen is a non-metal and has 1 valence electron. To attain a stable duplet electronic configuration, each hydrogen atom needs one more electron. As both the combining atoms are one electron short, none of them can donate an electron. Hence, they share one pair of electrons and attain a stable duplet configuration.

(a) Atomic orbit structure diagram for formation of hydrogen molecule is shown below:

(b) Atomic orbit structure diagram for formation of chlorine molecule is shown below:

(c) Atomic orbit structure diagram for formation of oxygen molecule is shown below:

(d) Atomic orbit structure diagram for formation of nitrogen molecule is shown below:

Atomic number of Cl is 17 and elect. config. is [2,8,7]. As both the Cl atoms require one electron to complete it's octet, hence, they both will share 1 electron and will attain a stable electronic configuration of the nearest noble gas — argon. Therefore, single covalent bond is formed during formation of a chlorine molecule.

Atomic number of O is 8 and elect. config. is [2,6]. As both the O atoms require two electrons to complete their octet, hence, they both will share 2 electrons and will attain a stable electronic configuration of the nearest noble gas — neon. Therefore, double covalent bond is formed during formation of a oxygen molecule.

(a) Atomic orbit structure diagram for formation of water molecule is shown below:

(b) Atomic orbit structure diagram for formation of ammonia molecule is shown below:

(a) Atomic orbit structure diagram for formation of carbon tetrachloride molecule is shown below:

(b) Atomic orbit structure diagram for formation of methane molecule is shown below:

Radical formation occurs when a covalent bond breaks symmetrically, with each atom retaining one electron of the shared pair. This results in the formation of two radicals. The process is called bond fission and is initiated by light, heat or certain chemicals.

A—B $\xrightarrow{\text{light energy}}$ A● + B●

Both A and R are true but R is not the correct explanation of A.

Reason — A is true as noble gases have completely filled valence shells making them chemically stable.
R is true as except noble gases, other elements do not have completely filled outermost shells.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

Both 2,8 and 2,8,8 can be correct.

Reason — The first shell can have a maximum of 2 electrons. Since element X has the same number of electrons in its first shell and in its outermost shell, its outermost shell also contains 2 electrons.

Thus, X may have electronic configuration:

• 2,8,2 — on losing 2 electrons, X²⁺ becomes 2,8
• 2,8,8,2 — on losing 2 electrons, X²⁺ becomes 2,8,8

Hence, both 2,8 and 2,8,8 are possible electronic configurations of X²⁺. Therefore, the question has two correct options unless the atomic number or period of element X is specified.

AB₄

Reason — Electronic configuration of A = 2, 4
Element A needs 4 electrons to attain Neon configuration as it has 4 valence electrons. Therefore, valency of A = 4.

Electronic configuration of B = 2, 8, 7
Element B needs 1 electron to attain Argon configuration as it has 7 valence electrons. Therefore, valency of B = 1.

$$\begin{aligned}\overset{\phantom{4}{4}}{\text{A}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{B}} \Rightarrow \underset{\phantom{1}{1}}{\text{A}} \space {\searrow}\mathllap{\swarrow} \space \underset{4}{\text{B}} \\[0.5em]\end{aligned}$$

AB₄ is the correct formula.

Water contains two hydrogen atoms and one oxygen atom. The hydrogen atom [1] has one electron in it's valence shell while the oxygen atom [2,6] has 6 electrons in it's valence shell. Two hydrogen atom share one electron each and two unshared pairs of electrons are left as lone pairs as shown in the diagram below :

In the case of ammonia, it contains three hydrogen atoms and one nitrogen atom. Nitrogen atom [2,5] has five valence electrons and hydrogen atom [1] has one valence electron. In ammonia, each of the three hydrogen atoms are bonded to the nitrogen atom by a pair of shared electrons. Thus, the nitrogen atom in ammonia is left with one lone pair of electrons as shown in the diagram below:

In methane, carbon has 4 valence electrons. All four electrons are used in forming four covalent bonds with hydrogen atoms, so no electrons remain unshared. Hence, methane has no lone pairs.

1. Sodium chloride [NaCl]
2. Methane [CH₄]
3. Water [H₂O]
4. Nitrogen [N ≡ N]
5. Oxygen [O = O]

1. As the atomic number of H is 1 and its electronic configuration is 1, it needs one electron to attain the nearest noble gas He configuration, i.e. 2 electrons in the first shell (duplet rule).
2. As the atomic number of O is 8 and its electronic configuration is 2,6, it needs two electrons to attain the nearest noble gas Ne configuration, i.e. 8 electrons in the valence shell (octet rule).
3. As the atomic number of N is 7 and its electronic configuration is 2,5, it needs three electrons to attain the nearest noble gas Ne configuration, i.e. 8 electrons in the valence shell (octet rule).
4. As the atomic number of C is 6 and its electronic configuration is 2,4, it needs four electrons to attain the nearest noble gas Ne configuration, i.e. 8 electrons in the valence shell (octet rule).
5. As the atomic number of Cl is 17 and its electronic configuration is 2,8,7, it needs one electron to attain the nearest noble gas Ar configuration, i.e. 8 electrons in the valence shell (octet rule).

1. E is a divalent metal as it has 2 electrons in the valence shell [electronic configuration 2,8,8,2] and it tends to lose two electrons in order to gain a stable octet configuration.
2. C is a non-metal as it's electronic configuration is 2,8,7 and it tends to gain one electron to attain a stable state.
3. Double covalent bond as the electronic configuration of A is 2,6 [non-metal], both A atoms will try to gain 2 electrons to attain a stable octet and none of the combining atoms are in a position to donate. Hence, they form the bond by sharing of 2 valence electrons and form a double covalent bond.
4. Electrovalent bond as the elect. configuration of D = [2,8,1] and C = [2,8,7], hence, D donates one electron and becomes a cation whereas C takes up one electron and becomes an anion. The attractive force between a cation and anion results in formation of an electrovalent bond.
5. Triple covalent bond as the electronic configuration of B is [2,5], hence, B needs 3 electrons to attain a stable octet configuration and hence forms a triple covalent bond.

1. As the electronic configuration of X is [2,8,1] and Y is [2,8,7], hence X donates one electron and Y accepts one electron in order to attain stable octet configuration. Hence, electron is transferred from X to Y.
2. Sharing of electrons mainly takes place between a pair of non-metals and as X [2,8,1] is a metal and Y is a non-metal [2,8,7]. Hence, electrons are not shared between 'X' & 'Y' during the formation of 'XY'
3. X is an atom and has no charge, whereas X¹⁺ is a cation and has a unit positive charge.
4. Y^1- has a stable electronic configuration [i.e., 2,8,8] as there are 8 electrons in the valence shell.
5. Electronic configuration of A is [2,8,8,1] and Y is [2,8,7], Hence, A is a metal and Y is a non-metal. Therefore, there will be transfer of 1 valence electron from A to Y and the compound formed will be an electrovalent compound.