1. Chemical bonds occur when atoms combine to form molecules.
2. The formation of chemical bond involves redistribution of electrons.
3. The force between any two atoms or a group of atoms that results in the
formation of a stable entity is called chemical bond.
4. Location of elements in the periodic table helps in predicting the type of bonding that will take place between atoms of the elements.
5. The electrons present in the outer most orbit of an atom are called valency electrons.
6. In the formation of chemical bond outer most electrons or valency electrons are only involved.
7. Noble gases are not involve in chemical reaction or chemical bonding due to presence of stable electrons. Completely filled configuration (ns2np6) except Helium (1s2)
8. Any species with eight electrons in the valence shell is stable.
9. The Lewis dot structures of the atoms of noble gases are shown below.
10. Chemical bond formation between atoms in terms of valency electrons was explained by the Kossel and Lewis.
11. Atoms get eight electrons in the outermost orbit by losing, gaining or sharing of electrons in the bond formation is called octet rule.
Ionic Bond
12. Ionic bond was proposed by Kossel.
13. Ionic bond is formed between atoms of two dissimilar elements due to transfer of electrons from the atom of one element to the other.
14. The positive ions (cations) and negative ions (anions), that are formed due to the transfer of electrons from the metal atoms to the non-metal atoms experience the electrostatic forces and get attracted to form chemical bond. As this bond is between charged particles known as ions, it is called ionic bond.
15. The electrostatic force of attraction between oppositely charged ions is called ionic bond or electrostatic bond or electro valent bond.
16. Ionic bond is a non directional bond.
17. NaCl, MgCl2, Na2O, AlCl3 etc are ionic compounds.
18. Sodium atom loses one electron to form Na+ ion and Chlorine atom gains one electron to form Cl− ion. Both ions get stable inert gas configuration. These oppositely charged ions get attracted towards each other due to electro static forces to form Sodium Chloride (NaCl). 
Formation of the compound NaCl from its ions
19. Magnesium atom loses two electrons to form Mg+2 ion and chlorine atom gains one electron to form Cl− ion. Both ions get stable inert gas configuration one Mg+2 ion is attracted by two Cl− ions by electrostatic forces to form magnesium chloride (MgCl2)
Mg(g)→ Mg+2(g) + 2 e−
2, 8,2 2, 8
2 Cl(g) + 2 e− → 2 Cl−(g)
2, 8,7 2, 8, 8
Mg+2 (g) + 2 Cl− (g) → MgCl2(s)
20. Ionic compounds in the crystalline state consist of orderly arranged cations and anions held together by electrostatic forces of attractions in three dimensions.
21. The number of ions of opposite charge that surround a given charge ion is known as the coordination number of that given ion.
22. In Sodium Chloride Crystal each Na+ ion is surrounded by six Cl− ions and each Cl− ion by six Na+ ions. In Sodium Chloride Crystal, the coordination number of Na+ is 6 and that of Cl− is also 6.
23. The tendency of elements by losing electrons is called the metallic character or electro positively. Elements with more electropositive character form cations.
24. The tendency of elements by gaining electrons is called the non metallic character or electronegativity. Elements with more electronegative character form anions.
25. Ionic bond is formed between atoms of elements with electronegativity difference equal to or greater than 1.9.
26. The tendency of losing electrons to form cations or gaining electrons to form anions depends on
i) Atomic Size
ii) Ionisation potential
iii) Electron affinity
iv) Electro negativity
Covalent Bond
27. The formation of covalent bond was proposed by G.N. Lewis.
28. The chemical bond formed by sharing of electrons between two atoms is called covalent bond.
29. In the covalent bond formation both the atoms contribute equal number of electrons.
30. The number of covalent bonds formed by an atom depends on the number of unpaired electrons in their valency shell and the number of electrons required to attain inert gas configuration.
31. The bond formed by sharing of one, two or three electron pairs between two atoms is called single bond (−), double bond (=) or triple bond (
) respectively.
32. In the formation of F2 molecule, each fluorine atom contributes one electrons for bond formation and one electron pair is shared between two atoms.
33. In the formation of O2 molecule, each Oxygen atom contributes two electrons for bond formation and two electron pairs are shared between two atoms to form a double bond between them.
34. In the formation of N2 molecule each nitrogen atom contributes three electrons for bond formation and three electron pairs are shared between two atoms to form a triple bond between them.
35. (i) In the formation of CH4 molecule, carbon atom contributes four electrons and four hydrogen atoms contributes one electrons each to form four C − H bonds.
(ii) In the formation of NH3 molecule, nitrogen atom contributes three electrons and three hydrogen atoms contribute one electron each to form three N − H bonds.
36. In the formation of H2O molecule, oxygen atom contributes two electrons and two hydrogen atoms contribute one electron each to form two O − H bonds.
37. The total number of covalent bonds that an atom of an element forms is called its covalency.
38. The distance between the nuclei of two atoms in a covalent bond is called bond length or bond distance.
39. Bond length is expressed in nm (nanometer) or (Angstrom Unit).
1nm = 10−9 m
1 Ao= 10−10 m
40. Electronic theory of valence fails to explain bond angles shapes of molecules, bond lengths and bond energies.
Valence shell electron pair repulsion theory
41. VSEPRT was proposed by Sidgwick and Powell they it was improved by Gillespie and Nyholm.
42. VSEPRT considers electrons in the valence shells which are in covalent bonds and in lone pairs as charge clouds that repel one another and stay as far apart as possible. This is the reason why molecules get specific shapes.
43. Lone pairs occupy more space around the central atom than bond pairs.
44. If two bond pairs in the valence shell of the central atom, the shape of the molecule is linear and its bond angle is 180°.
45. In BeCl2 molecule, the central atom contains only two bond pairs. So the shape of the molecule is linear and its bond angle is 180°.
46. If three bond pairs in the valence shell of the central atom, the shape of the molecule is trigonal − planar or planar triangular and its bond angle is 120°
47. In BF3 molecule, boron atom contains only three bond pairs. So the shape of the molecule is trigonal planar and its bond angle is 120°
48. If four bond pairs in the valence shell of the central atom, the shape of the molecule is tetrahedral and its bond angle is 109° 28'.
49. In methane molecule, carbon atom contains four bond pairs. So the shape of the molecule is tetrahedral and its bond angle is 109° 28'.
50. If three bond pairs and one Lone pair in the valence shell of the central atom, the shape of the molecule is pyramidal and Lone pair bond angle is reduced to 107° 48' due to high Lone pair-bond pair repulsions.
51. In NH3 molecule, nitrogen atom contains three bond pairs and one Lone pair. So the shape of the molecule is pyramidal and its bond angle is 107°48'.
52. If two bond pairs and two Lone pairs in the valence shell of the central atom, the shape of the molecule is angular or V shape or bent shape and its bond angle is 104° 31'
53. in H2O molecule, Oxygen atom contains two bond pairs and two Lone pairs. So the shape of the molecule is angular or bent shape or v shape and its bond angle is 104° 31'
54. VSEPRT theory mainly fails in explaining the strengths of the bonds.
55. VSEPRT theory could not say anything extra about the electronic nature of covalent bonds.
Valence bond theory
56. Valence bond theory was proposed by Linus Pauling.
57. A covalent bond between two atoms is formed when the two atoms approach each other closely and one atom overlaps its valence orbital containing unpaired electron, the valence orbital of the other atom that contains the unpaired electron of opposite spin. The so formed paired electrons in the overlapping orbitals are attracted to the nuclei of both the atoms. This bonds the two atoms together.
58. In the formation of H2 molecule, the 1s orbital of one 'H' atom containing an unpaired electron overlaps the '1s' orbital of the other 'H' atom containing unpaired electron of opposite spin giving H - H bond and H2 molecule.
59. The greater overlapping of the orbitals that form the bond, the stronger will be the bond. This gives a directional character to the bond when other than 'S' orbitals are involved.
60. Each bonded atom maintains its own atomic orbitals but the electron pair in the overlapping orbitals is shared by both the atoms involved in the overlapping.
61. If two atoms form multiple bonds between them the first bond is due to theoverlap of orbitals along the inter - nuclear axis giving a stronger sigma (σ) bond. After formation of (σ) bond the other bonds are formed due to the overlap of orbitals side wise or laterally giving weaker (π) bonds.
62. In the formation of Cl2 molecule, the 3pz orbital of one chlorine atom containing an unpaired electron overlaps the 3pz orbital of other chlorine atom that contains unpaired electron of opposite spin.
63. σ Bond is stronger than π bond.
64. σ bond exists independent Molecules having single bonds have only σ bonds.
65. π bond has no independent existence. It exists only in the presence of a σ bond.
66. In a double bond one σ and one π bond are present.
67. In a triple bond one σ and two π bonds are present.
68. Molecules having double bond are O2, ethylene (C2H4), CO2 etc.
69. Nitrogen (N2), Acetylene (C2H2), etc. have triple bonds.
Hybridisation
70. Hybridisation of atomic orbitals was proposed by Linus Pauling.
71. The phenomenon of intermixing of atomic orbitals of almost equal energy which are present in the outer shells of the atom and their reshuffling or redistribution into the same number of orbitals but with equal properties like energy and shape is called hybridisation.
72. In BeCl2 molecule, Beryllium atom undergoes sp hybridisation in the excited state. Shape of BeCl2 is linear and its bond angle is 180º.
73. In BF3 molecule, borom atom undergoes SP2 hybridisation in the excited state. The shape of BF3 molecule is planar triangular and its bond angle is 120.
74. In NH3 molecule, nitrogen atom undergoes SP3 hybridisation. The shape of NH3 molecule is pyramidal and due to high Lone pair - bond pair repulsion the bond angle decreases to 107° 48'.
75. In H2O molecule, oxygen atom undergoes Sp3 hybridisation. The shape of H2O molecule is angular and due to higher Lone pair - Lone pair repulsion the bond angle decreases from 109° 28' to 104° 31'.
76. In ionic compounds there exist stronger electrostatic forces of attractions between the oppositely charged ions. So they are solids with high melting points and boiling points.
77. Ionic compounds are soluble in polar solvents.
78. Chemical reactions between ionic compounds in solutions are very fast.
79. Covalent compounds are gases or liquids at room temperature.
80. Covalent compounds have low melting points and low boiling points.
81. Covalent compounds are soluble in non polar solvents.
82. Chemical reactions between covalent compounds are moderate or very slow.
83. If the covalent bond is between atoms of two different element, the shared electron pair shift more towards the atom of more electro negative element, so that atom bears as partial negative charge and the less electro negative atom bears a partial positive charge.
84. The molecule which contains partial negative charge and partial positive charge is called a polar molecule and the bond is called a polar covalent bond or partial ionic and partial covalent bond.
Conceptual flow chart
