These notes for CBSE Class 11 Chemistry Chapter 4, "Chemical Bonding and Molecular Structure," explain the fundamental concepts of chemical bonding. It details the Octet Rule, where atoms aim for eight electrons in their outer shell. The notes define chemical bonds as forces holding atoms together. It elaborates on Ionic Bonds, formed by electron transfer between metals and non-metals, and the associated Lattice Enthalpy. Electrovalency, the number of electrons lost or gained, is also discussed. Covalency, involving electron sharing, is explained through single, double, and triple covalent bonds. The formation of covalent bonds is favored by specific ionization enthalpies and electronegativities. The chapter introduces Polar Covalent Bonds, Coordinate Bonds (dative bonds), and defines key terms like Bond Length, Bond Angle, Bond Enthalpy, and Bond Order. Resonance and Dipole Moment are explained. Finally, Sigma and Pi bonds, formed by different orbital overlaps, and Hydrogen Bonds are covered. Hybridization, the mixing of atomic orbitals, is also introduced. These notes are ideal for revising the chapter's core concepts for exams.
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During a chemical reaction the atoms tend to adjust their electronic arrangement in such a way that they achieve 8 e- in their outermost electron. This is called octet rule.
the chemical force which keeps the atoms in any molecule together is called a chemical bond.
The columbic force of attraction which holds the appositively charged ions together is called an ionic bond. An ionic bond is formed by the complete transfer of one or more electrons from the atom of a metal to an atom of non- metal.
The molar enthalpy change accompanying the complete separation of the constituent particles that compose of the solids (such as ions for ionic solid, molecules for molecular solids) under standard conditions is called lattice enthalpy (?lHo). The lattice enthalpy is a positive quantity.
The number of electrons lost or gain by an atom of an element is called as electrovalency.The element which give up electrons to form positive ions are said to have positive valency, while the elements which accept electrons to form negative ions are said to have negative valency.
It is favoured by (i) the low ionisation enthalpy of a metallic element which forms the cations, (ii) High electron gain enthalpy of non- metallic element which forms the anions, (iii) Large lattice enthalpy i.e; the smaller size and the higher charge of the atoms.
The number of electrons which an atom contributes towards mutual sharing during the formation of a chemical bond called its covalency in that compound.
A covalent bond formed by the mutual sharing of one pair of electrons is called a single covalent bond, or simply a single bond. A single covalent bond is represented by a small line (?) between the two atoms.
A covalent bond formed by the mutual sharing of two pair of electrons is called a double covalent bond, or simply a double bond. A double covalent bond is represented by two small horizontal lines (=) between the two atoms. E.g. O=O, O=C=O etc.
A covalent bond formed by the mutual sharing of three pair of electrons is called a triple covalent bond, or simply a triple bond. A triple covalent bond is represented by three small horizontal lines (?) between the two atoms. E.g. N?N, H-C?C-H etc.
Formation of a covalent bond is favoured by (i) High ionisation enthalpy of the combining elements. (ii) Nearly equal electron gain enthalpy and equal electro-negativities of combining elements. (iii) High nuclear charge and small atomic size of the combining elements.
The bond between two unlike atoms which differ in their affinities for electrons is said to be polar covalent bond. E.g. H-Cl
The bond formed when one sided sharing of electrons take place is called a coordinate bond. Such a bond is also known as dative bond. It is represented by an arrow (?) pointing towards the acceptor atom. E.g. H3N?BF3
Bond Length : Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule
Bond Angle : It is defined as the angle between the orbitals containing bonding electron pairs around the central atom in a molecule/complex ion
Bond Enthalpy : It is defined as the amount of energy required to break one mole of bonds of a particular type between two atoms in a gaseous state.
Bond Order : In the Lewis description of covalent bond, the Bond Order is given by the number of ondsetween the two atoms in a molecule
Resonance : whenever a single Lewis structure cannot describe a molecule
accurately, a number of tructures with similar energy, positions of nuclei, bonding and non-bonding pairs of electrons are taken as he canonical structures of the
hybrid which describes the molecule accurately
Dipole moment : The product of the magnitude of the charge and the distance between the centres of positive and negative charge.It is a vector quantity and is represented by an arrow with its tail at the positive centre and head pointing towards a negative centre. Dipole moment (?) = charge (Q) × distance of separation (r)
SIGMA BOND : A covalent bond formed due to the overlapping of orbitals of the two atoms along the line joining the two nuclei (orbital axis) is called sigma (?) bond. For example, the bond formed due to s-s and s-p, p-p overlapping along the orbital axis are sigma bonds.
A covalent bond formed by the side wise overlapping of p- or d- orbitals of two atoms is called as pi (?) bond. For example, the bond formed due to the sideways overlapping of the two p- orbitals is a pi- bond.
The bond between the hydrogen atom of one molecule and a more electro- negative element of same or another molecule is called as hydrogen bond.
The process of mixing of the atomic orbitals to form new hybrid orbitals is called hybridization. All hybrid orbitals of a particular kind have equal energy, identical shapes and are symmetrically oriented in shape. The hybrid orbitals are designed according to the type and the atomic orbitals merging together, e.g.,
The Octet Rule states that atoms tend to adjust their electronic arrangement during a chemical reaction to achieve 8 electrons in their outermost shell.
An ionic bond is formed by the complete transfer of one or more electrons from a metal atom to a non-metal atom, creating oppositely charged ions that attract each other.
Electrovalency is the number of electrons lost or gained by an atom, while covalency is the number of electrons contributed by an atom for mutual sharing in a chemical bond.
Covalent bonds can be single (sharing one pair of electrons), double (sharing two pairs), or triple (sharing three pairs).
A coordinate bond, also known as a dative bond, is formed when one atom shares a pair of electrons with another atom, with the sharing being one-sided.
Sigma bonds are formed by the head-on overlapping of atomic orbitals along the internuclear axis, while pi bonds are formed by the sideways overlapping of p or d orbitals.
Hybridization is the process where atomic orbitals of similar energy mix to form new hybrid orbitals that are identical in shape and energy, and are symmetrically oriented.
A hydrogen bond is an attractive force between the hydrogen atom of one molecule and a more electronegative element (like oxygen, nitrogen, or fluorine) of the same or another molecule.
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