Tiêu đề 1. CW_CHEMICAL BONDING.pdf ✅

VII -Chemistry (Vol-II) 2 Narayana Group of Schools Olympiad Class Work Book Over the seven decades of his scientific career, Pauling’s research interests were amaz- ingly wide-ranging and eclectic. He made important discoveries in many different fields of chemistry — physical, structural, analytical, inorganic, and organic chemis- try, as well as biochemistry. He used theoretical physics, notably quantum theory and quantum mechanics, in his investigations of atomic and molecular structure and chemical bonding. He ventured into metallurgy and mineralogy through the study of atomic structures and bonding of metals and minerals and, with his colleagues, pub- lished the structures of hundreds of inorganic substances, including topaz and mica. In both theoretical and applied medicine he made important discoveries in genetic diseases, haematology, immunology, brain function and psychiatry, molecular evo- lution, nutritional therapy, diagnostic technology, statistical epidemiology, and bio- medicine. Linus Pauling 28 -Feb-1901 - 19 -Aug - 1994 Pauling was one of the founder of the fields of quantum chemistry and molecular biology. His contributions to the theory of the chemical bond include the concept of orbital hybridisation and the first accurate scale of electro negativities of the elements. Orbital hybridisation (or hybridization) is the concept of mixing atomic orbitals into new hybrid orbitals (with different energies, shapes, etc., than the component atomic orbitals) suitable for the pairing of electrons to form chemical bonds in valence bond theory. Hybrid orbitals are very useful in the explanation of molecular geometry and atomic bonding properties and are symmetrically disposed in space. Although sometimes taught together with the valence shell electron-pair repulsion (VSEPR) theory, valence bond and hybridisation are in fact not related to the VSEPR model

VII -Chemistry (Vol-II) 4 Narayana Group of Schools Olympiad Class Work Book 2) In a similar way, when two atoms approach each other, forces of attractions and repulsions operate in between them. 3) The forces of attractions are between the nucleus of one atom and the electrons of other atom. 4) The forces of repulsions are between two nuclei as well as in between the electrons of two atoms. 5) If the attractive forces just balance the repulsive forces, then the total potential energy of the system decreases and a chemical bond results. 6) At the distance shorter than equilibrium distance, repulsive forces operate pre- dominantly. Then no chemical bond is formed. 7) Chemical bond is said to be formed at the lowest energy of the curve. B o n d e n ergy Bond length - Attra ctio n + R e p ulsio n Internuclear Distance (pm) Potential Energy Vs internuclear Distance Between two atoms P ote ntial E n ergy (KJ / m ol) H H H H H H 8) The internal energy of a molecule is less than the sum of internal energies of indi- vidual atoms in that molecule. Example: In the formation of one mole of Hydrogen, 104 K.Cal of energy is released. 2 H H H K cal   104 . This suggests that Hydrogen molecules have less energy than its constituent hydro- gen atoms by about 104 K.cal/mole. So Hydrogen molecules are stable than Hydro- gen atoms, and the process is exothermic REASONS FOR NON REACTIVITY OF NOBLE GASES Electronic configuration of Noble Gases: Noble gases are monoatomic in nature. They do not form molecules either with their own atoms or react chemically with any other element. Why?