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μ = μ₁ + μ₂ = μ₁ + (-μ₁) = 0

(for CO₂)

Octahedral

The shape of sulphur hexafluoride is Octahedral.

1. The metallic lustre is due to the reflection of light by the electron cloud.

2. As the metallic bond is strong enough. the metal atoms are reluctant to break apart into a liquid or gas, so the metals have high melting and boiling points.

(a) Statements I and II are correct and statement II is the correct explanation of statement I.

High thermal conductivity of metals is due to thermal excitation of many electrons from the valence band to the conduction band.

(a) Both (A) and (R) are correct and (R) is the correct explanation of(A).

(a) The metallic luster is due to reflection of light by the electron cloud.

Correct Option is : (C) 3

Molecular Configuration of \(N_2\)

\( 15 \sigma^2 \ 15 \sigma^{\ast 2} \ 25 \sigma^2 \ 15 \sigma^{\ast 2} \ 2p_x \sigma^2 \ 2p_y \pi^2 = 2p_z{\pi^2}\)

Bond Order = \(\frac{bonding \ e^- \ - \ antibonding \ e^- }{2}\)

= \(\frac{10-4}{2}\) = 3

Option : (C) 3 

(b) O₂ molecules is paramagnetic

Potassium – K and Calcium – •Ca•

Ionic compounds generally exists as solids and they have very high melting and boiling points and they conduct electricity in aqueous or molten state. So first and second statements are true.

The electronic configuration of molecules provides the following information :

• Stability of molecules: If the number of electrons in bonding MOs is greater than the number in antibonding MOs the molecule is stable.
• Magnetic nature of molecules: If all MOs in a molecule are completely filled with two electrons each, the molecule is diamagnetic (i.e., repelled) by magnetic field. However, if at least one MO is half-filled with one electron, the molecule is paramagnetic (i. e., attracted by magnetic field).
• Bond order of molecule : The bond order of the molecule can be calculated from the number of electrons in bonding MOs (N_b) and antibonding MOs (N_a).

The element with electronic configuration 2, 8,1 is sodium which is a metal. Similarly the element with electronic configuration 2, 8, 7 is chlorine which is a non-metal. The electronegativity difference between these two elements is more than 1.9 so they form ionic bond.

Molecules have lower energy than that of the combined atoms. Molecules are more stable than atoms since chemical species with lower energy are more stable.

Electrovalent crystalline solids do not conduct electricity because the oppositely charged ions in them are held together by a strong electrostatic force of attraction. These ions occupy fixed position in the crystals and do not move when an electric field is applied. . 

A systematic arrangement of electrons in the atomic orbits is called electronic configuration.

(a) Electrovalent compounds in the solid state do not conduct electricity because movement of ions in the solid state is not possible due to their rigid structure. But these compounds conduct electricity in the molten state. This is possible in the molten state since the electrostatic forces of attraction between the oppositely charged ions become weak. Thus, the ions move freely and conduct electricity.

(b) The atoms of covalent compounds are bound tightly to each other in stable molecules, but the molecules are generally not very strongly attracted to other molecules in the compound. On the other hand, the atoms (ions) in electrovalent compounds show strong attractions to other ions in their vicinity. This generally leads to low melting points for covalent solids, and high melting points for electrovalent solids.

(c) Electrovalent compounds dissolve in polar solvents like water because the forces of attraction between positive and negative charges become weak in water. But since covalent compound are made up of molecules, they do not ionize in water and hence do not dissolve in water.

(d) Since it takes a lot of energy to break the positive and negative charges apart from each other, the ionic compounds are so hard. But on applying stress, Ions of the same charge are brought side-by-side and so the opposite ions repel each other and crystal breaks into pieces.

(e) Since polar covalent compounds are made up of charged particles, they conduct electricity in aqueous solution

The solid is ionic in nature as the oppositely charged ions are being held tightly by strong intermolecular force of attraction and that's the reason for its high melting point and solubility in water

Ionic compounds exhibit high melting and boiling points.

(b) Mg

M would most likely be in the group in which Mg  is placed.

OF₂ a neutral molecule which is isoelectronic with ClO^-.

Sp² is the state of hybridisation of Carbon in CO₃^2- ion.

The correct option is- (c)AsF₅

The correct option is- (c) HCHO

The correct option is-(c) IF₇

The correct option is- (a) O₃

The correct option is- (d) CF₂Cl₂

(a) BrF₃ , CIF₃

The correct option is- (c) BeCl₂

The correct option is-(d) 2 3 4 1

The correct answer is:- (c) 2 3 4 1

The correct option is:-(b) 3 4 1 2

The correct option is-(a) 3 4 2 1

(i) N₂  

(iv) O₂^2–

(i) Magnesium hydroxide - milk of magnesia an antacid 

magnesium sulphate - laxative & anti convulsant. 

potassium nitrate - igniter in fireworks & matchstics. 

sodium carbonate - as washing soda. 

(ii) lithium carbonate is used for treatment of manic depression (which is due to over anxiety & excitement) 

(iii) Zinc oxide. 

(iv) Citric acid & sulphuric acid. 

(v) (a) Sodium hypochlorite. 

(b) Sodium hydroxide. 

(c) sodium flouride. 

1. Electrovalent or ionic bond: The chemical bond formed between two atoms by transfer of one or more electrons from the atom.

2. Electrovalent or ionic compound: The chemical compound formed as a result of transfer of one or more electrons from atom. 

After studying this unit the student should be able to : 

• define the chemical bond and the cause of chemical bonding. 
• explain different types of bonds formed by the atoms. l differentiate between ionic and covalent bonds. 
• draw the shapes and geometries of various molecules by using VSEPR Theory. 
• understand the difference between valence band theory and molecular orbital theory. 
• explain the hybridization and its relation to the shape of molecules. 
• write the electronic configuration in molecular orbitals for simple diatomic molecules. 
• calculate the bond order on the basis of electron distribution in various molecular orbitals. 
• predict the bond strength and magnetic properties of molecules on the basis of MO theory. 
• explain the effect of hydrogen bonding on the properties of molecules.

It is observed that the atoms of all the elements, except those for noble gases, tend to remain in combined state with the atoms of same or other element. They do not exist as single atoms under ordinary conditions. Such atomic aggregates occur as molecules or as giant network. A molecule may be defined as a small electrically neutral cluster or group of mutually bonded atoms. A chemical bond may be defined as “binding force between two atoms in a molecule”.

Chemical bonding is the attractive force that holds or binds constituents were atoms, ions or molecules together in a substance.

The bond formed, as a result of the electrostatic attraction between the positive and negative ions are termed as the electrovalent bond.

NH₃ molecule: According to VSEPR theory, NH₃ should have tetrahedral shape due to presence of 4 electron pairs. The presence of lone pair on nitrogen causes greater repulsion to the bond pairs. As a result of which the three N-H bonds move slightly closer. So it decreases the normal tetrahedral bond angle of 109.50 to 1070 . Therefore, ammonia has irregular geometry. Since one of the tetrahedral position is occupied by lone pair, the shape of ammonia molecule is pyramidal.

Option : (D) square pyramidal

(d) CCI₄ – covalent bond

(d) BF₃ – 120°

(a) AB₃L : Bent. 

Actually AB₃L is pyramidal.

1. In CH₄ , NH₃ and H₂O the central atom undergoes sp³ hybridisation. But their bond angles are different due to the presence of lone pair of electrons.

2. It can be explained by VSEPR theory. According to this theory, even though the hybridisation is same, the repulsive force between the bond pairs and lone pairs arc not same.

3. Bond pair-Bond pair < Bond pair – Lone pair < Lone pair – Lone pair So due to the varying repulsive force the bond pairs and lone pairs are distorted from regular geometry and organise themselves in such a way that repulsion will be minimum and stability will be maximum.

4. In case of CH₄ , there are 4 bond pairs and no lone pair of electrons. So it remains in its regular geometry. i.e., tetrahedral with bond angle 109° 28’.

5. H₂O has 2 bond pairs and 2 lone pairs. There is large repulsion between lp – lp. Again repulsion between lp – bp is more than that of 2 bond pairs. So 2 bonds are more restricted to form inverted V shape (or) bent shape molecule with a bond angle of 104° 35’.

6. NH₃ has 3 bond pairs and 1 lone pair. There is repulsion between lp – bp. So 3 bonds are more restricted to form pyramidal shape with bond angle equal to 107° 18’.

(c) CH₄ – T-shape

Octet Rule- Every element tries to acquire 8 electrons in its outermost orbit by loosing or gaining or sharing electron.

Significance – Most of the molecules are formed by following octet rule eg. N₂,O₂,Cl₂,Br₂ etc it is useful for understanding most of the organic compounds and it applies mainly to the second period elements of the periodic table.

Limitations- Although octet rule is very useful but is not universal.In some compounds, the number of electron surrounding the central atom is less than 8.In NO,NO₂ octet rule is not satisfied they are odd electron molecule In PF₅,SF₆,IF₇ these expanded octets or super octets i.e. 10,12 and 14 electrons respectively after sharing.

Formation of electron deficient compounds like BeCl₃ , BF₃ , AlCl₃ . Central atom has less than 8e .

Formation of hypervalent compounds like PCl₅, SF₆, IF₇, H₂SO₄ in which central atom has more than 8 electrons.

Formation of compounds of noble gases like XeF₂, XeF₄, XeF₆ .

Odd electron molecules like NO, NO₂.