BOND: a force that acts b/w 2 or more atoms to hold them together as a molecule.
- Lowerisation of energy: Bonded state is more stable coz has lower potential energy than unbonded state.
- 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
Some facts regarding ionic solids:
- Hydration of ionic solid involves evolution of heat, weakening of attractive force, dissociation into ions.
- 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
- 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)
- Coordinate bond
- Bond b/w Lewis acid and Lewis base.
- L.B. l.p. on central atom available for donation
e deficient due to Incomplete octet/ vacant p/d orbital/ high +ve charge/size ratio L.A.
THEORIES OF BOND FORMATION
- Kossel, Lewis approach(electronic theory of covalence)
field theory Crystal
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.)
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.