Here students can locate TS Inter 1st Year Chemistry Notes 3rd Lesson Chemical Bonding and Molecular Structure to prepare for their exam.
TS Inter 1st Year Chemistry Notes 3rd Lesson Chemical Bonding and Molecular Structure
→ The force of attraction between the constituent atoms of a molecule is called chemical bond.
→ The principle of attaining eight electrons in the outermost shell of an atom for attaining stability is called octet rule.
→ The electrostatic force of attraction bet-ween oppositely charged ions formed by the transfer of electrons is called Ionic Bond or Electrovalent Bond.
→ The amount of energy released, when one mole of ionic substance is formed from its constituent oppositely charged ions separated by infinite distance are brought nearer together, is called lattice energy.
→ Born – Haber cycle is used for the indirect determination of lattice energy. This method is based on Hess’s law.
→ The smallest part of ionic substance, which develops the entire crystal on repetition in three dimensional space is called unit cell.
→ Ionic substances are polar and are soluble in polar solvents like water and are insoluble in non-polar solvents like Benzene etc.
→ Covalent bond is formed due to mutual sharing of electrons. This is also called electron-pair bond.
→ Molecules which have less number of electrons on the central atom than octet are called electron deficient molecules.
Ex : BeCl2, BF3 etc.
→ The covalent bond formed by head on overlap of half-filled orbitals is called sigma bond.
→ Sigma bond is a stronger bond than a pi bond because the extent of overlapping is more in sigma bond than in a pi bond.
→ VSEPR theory explains the shapes and bond angles of molecules without reference to the theory of hybridisation.
→ Presence of lone pair distorts the structure and decreases the bond angle.
→ The average inter – nuclear distance bet-ween bonded atoms is called bond length.
→ The amount of energy required to break a mole of covalent bonds is called bond energy.
→ The process of inter-mixing of atomic or-bitals of nearly same energy of an atom and forming the same number of identical new orbitals is called hybridisation.
→ A pure covalent bond is formed by equal sharing of bonded electrons, between two identical atoms.
→ A polar covalent bond is formed by unequal sharing of bonded electrons.
→ The product of charge and inter-nuclear distance is called Dipolemoment. It is a vector quantity and is measured in debye units.
→ Bond formed due to mutual sharing of electron pair, but shared pair belonging to only one of the atoms involved in the bond is called coordinate covalent bond (or) dative bond.
→ The weak electrostatic bond between a covalently bonded H atom and a highly E.N. atom is called hydrogen bond.
→ The force of attraction that holds the metal atoms firmly together in a metallic crystal is called metallic bond.
→ The number of electrons an atom contri-butes towards covalent bond formation in a molecule is known as its covalency.
→ The number of electrons lost or gained by an atom, during the formation of ‘ionic compound’, is its ‘electrovalency’.
→ Molecular orbital theory (M.O.T) was proposed by Hund and Mulliken. The m.o’s are formed by the method called linear combination of atomic orbitals’ (LCAO method).
→ Order of energy levels of m.o’s
(a) In Li2, Be2, B2, C2 and N2 molecules :
σ1s < σ*1s < σ*2s < σ*2s < π2Py
= π2Pz < σ2Px < π2Py = π2Pz < σ*2Py
(b) In O2, F2 and Ne2 molecules :
σ < σ*1s < σ2s < σ*2s < σ2Px < π2Py
= π2Pz < π*2Py = π2Pz < σ*2Px