Periodic table 0 IA IIA transition metals IIIB

Periodic table 0 IA IIA transition metals IIIB IVB VB VIBVIIB VIIIB post. IIIA IVA VA VIIA transition metals IB IIB

Bonding in Solids e e repulsive Coulomb interaction between ions repulsive Coulomb interaction between electrons attractive Coulomb interaction between ions and electrons kinetic energy of electrons

Molecular (van der Waals) bond Crystals of “inert” gases of group 0: Ar, Kr, Xe, Rn e e m 1 m 2 R Van-der Waals, London or fluctuating dipole interaction

Molecular (van der Waals) bond atom 1 atom 2 electron charge distribution -1/4

IONIC bond Crystals: Na. Cl, Cs. Cl, Ca. Cl 2 Na + Energy balance Cl Na+ Cl- cohesive energy + 7. 9 e. V

IONIC bond: Madelung constant R Madelung constant

IONIC bond: Madelung constant Na. Cl~ 1. 75 Cs. Cl~1. 76 Zn. S (cubic)~1. 64

Covalent bond Crystals: C, Si, Ge, H Covalent bond is formed by two electrons, one from each atom, localised in the region between the atoms (spins of electrons are anti-parallel ) Example: Carbon 1 S 2 2 p 2 C C 3 D Diamond: tetrahedron, cohesive energy 7. 3 e. V 2 D

Covalent bond Energy Hydrogen molecule H 4 1 S 1 S H atom Methane molecule H 2 molecule H atom C H 1 H 3 H 2

Covalent bond Atoms in group III, IV, V, &VI tend to form covalent bond Filling factor T. : 0. 34 F. C. C : 0. 74

Metallic bond Atoms in group IA-IIB let electrons to roam in a crystal. Free electrons glue the crystal Attract Repel e. Attract Repel Na+ Attract e- Additional binding due to interaction of partially filled d – electron shells takes place in transitional metals: IIIB - VIIIB

The Hydrogen bond is formed between the most electronegative atoms: F, O and N. Bonding energy is ~ 0. 1 ev Bonding in DNA molecule F- N H+ C N sugar N C H C H C N C C H adenine O C N N H C C H H H F- N sugar thymine

Bonding in Solids Melting point (K) Molecular crystals Metals Ionic crystals W(3683) C(<3500) BN(3270) 3000 Mo(2883) Pt(2034) Fe(1808) 2000 1000 0 Covalent crystals organic crystals Cu(1336) Al(933) Pb(600) Na(371) Hg(234) Si. O 2(2001) Li. F(1143) KCl(1063) Si(1683) Ge(1240)