Chemical Bonding

CHEMICAL BONDING BOND: a force that acts b/w 2 or more atoms to hold them together as a molecule. Reasons 1. Lowerisation of energy: Bonded state is more stable coz has lower potential energy than unbonded state. 2. Octet: old rule, disregarded now. Actually complete octet was assumed to be most stable. TYPES OF BONDS 1. Chemical bond 2. Force of Attraction 3. Typical bonds . 1. Ionic Bond or electrovalent bond  forms when ease of formation of ions, high lattice energy  complete transfer of e  one ion good donor(low IE), other good acceptor(high EA)  ΔEN increases, tendency to form I.B. increases.  Non directional Electrovalence: no. of e gained/ lost by any atom during bond formation (no sign) Ionic solids are  High melting & boiling  Bad conductor in solid state  Soluble in polar solvents  Good conductor in liquid and molten state  Isomorphous  Crystalline Some facts regarding ionic solids: 1. Hydration of ionic solid involves evolution of heat, weakening of attractive force, dissociation into ions. 2. Most of them: have 3-D network structure, do not exhibit space isomerism (non-directional bonds), and ionization is always endothermic. 2. Covalent Bonds  Force of attraction b/w nucleus of 1 atom and e cloud of another atom  Sharing of e  Types: single, double, triple : polar, nonpolar  directional  low melting, boiling point  Less conducting. conduction is due to auto-protolysis / self-ionization Covalence: no. of e involved in sharing (of any one atom) 3. Coordinate bond  Bond b/w Lewis acid and Lewis base.  L.B. l.p. on central atom available for donation  L.A. e deficient due to Incomplete octet/ vacant p/d orbital/ high +ve charge/size ratio THEORIES OF BOND FORMATION

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Kossel, Lewis approach(electronic theory of covalence) VSEPR VBT MOT Crystal field theory

Lewis dot structures  Central atom: connected to max. atoms, least electronegative, covalence>1, less in number, can’t be H or F  e.g. Cl2O: O, ClO2: Cl, NOCl: N, N2O: N  Exceptions of basicity: H3PO4:1; H4P2O5:2. NAMING OF ACIDS Parent acid : 2 types, ous (lower O.S.), ic(higher O.S.) Meta prefix: elimination of 1 water molecule from 1 molecule of P.A. e.g. HPO3 is metaphosphoric acid SO3 is not metasulphurus acid actually at least one H is compulsory in acids. It’s an acid anhydride. Ortho prefix: used for P.A.when its meta form is possible. e.g. H3BO3 is orthoboric acid. Orthophosphorous acid is an exception.(H3PO3) Pyro prefix: 2 P.A.- (H2O). e.g. H4P2O7 is pyrophosphoric acid. Hypo prefix: P.A.(ous )- O .e.g. H3PO2 is hypophosphorous acid. Per prefix: P.A.(ic) +O.e.g. HNO4 is pernitric acid or peroxynitric acid(-O-O- linkage is present) Sub: oxides for which no. of O atoms is less than no. of central atoms. E.g. C3O2 Salts of ic:ate, Salts of ous:ite. Replaceble H are involved in naming. e.g. NaH2PO4 is sodium dihydrogen phosphate but NaHPO3 is sodium phosphate.