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CHEMICAL BONDING

CHEMICAL BONDING . Topics Covered. I ntroduction O ctet rule D ifferent types of bonding Valency Bond Theory. What is a Chemical Bond?. Na +. Cl -. Chemical bonds. Force of attraction holding group(s) of atoms . But why bonds are formed ??.

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CHEMICAL BONDING

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  1. CHEMICAL BONDING

  2. Topics Covered • Introduction • Octet rule • Different types of bonding • Valency Bond Theory

  3. What is a Chemical Bond? Na+ Cl- Chemical bonds Force of attraction holdinggroup(s) of atoms But why bonds are formed ?? Better stability against chemical reagents

  4. Octet rule two electrons in the valenceshell (1s2) + Cl Na Na Cl - 2 8 7 2 8 2 8 1 2 8 8 Ne Very reactive Very reactive Ar Atoms noble gas configuration to attain betterstability.

  5. Limitation of octet rule In SF6, ‘S’ has twelve electron in itsvalence shell, leads to minimisation of energy.Other examples are: PCl5, BF3

  6. Ionic Covalent Sigma bond Pi bond Co-ordinate or dative Metallic Bonding

  7. Formation of ionic bond

  8. Covalent bond Triple bond Double bond Formed by mutual sharing of electrons Covalent bonds

  9. Formation of covalent bond non-polar covalent bond between two carbon atomspolar covalent bond between carbon and hydrogen atoms.

  10. Illustrative Problem electrostatic force of attraction. Ionic bond overlap of atomic orbitals covalent bond Covalent bonds are called directional while ionic bonds are called non-directional -explain Solution: p and d-orbitals generate directional covalent bond.

  11. Orbital Overlap Concept s-s s-p p-p + + + Strength of these sigma bonds is in the order: p-p > s-p >s-s sigma bond forms due to end-to-end or head-on overlap

  12. Orbital Overlap Concept or + This is formed by lateral or sideways overlap which is possible for p or d-orbitals. Sigma bond is stronger than pi bond due to greater extent of overlap.

  13. Formed by head-on overlapping of s-s or s-p or p-p or any hybrid orbital Formed by side ways overlapping of unhybridised p-orbital First bond between any two atoms is always sigma Rest are p bonds In plane of molecule Perpendicular to plane of molecule Stronger as compared to p bond Weaker as compared to s bond Difference between sigma and pi bonds

  14. Valence Bond (VB) Theory, the theory we will explore, describes the placement of electrons into bonding orbitals located around the individual atoms from which they originated. COVALENT BOND FORMATION (VB THEORY) In order for a covalent bond to form between two atoms, overlap must occur between the orbitals containing the valence electrons. The best overlap occurs when two orbitals are allowed to meet “head on” in a straight line. When this occurs, the atomic orbitals merge to form a single bonding orbital and a “single bond” is formed, called a sigma () bond.

  15. MAXIMIZING BOND FORMATION In order for “best overlap” to occur, valence electrons need to be re-oriented and electron clouds reshaped to allow optimum contact. To form as many bonds as possible from the available valence electrons, sometimes separation of electron pairs must also occur. We describe the transformation process as “orbital hybridization” and we focus on the central atom in the species...

  16. Hybridization of Be in BeCl2 Hybrid sp orbitals: 1 part s, 1 part p Atomic Be: 1s2 2s2

  17. FORMATION OF BeCl2: Each Chlorine atom, 1s22s22p63s23p5, has one unshared electron in a p orbital. The half filled p orbital overlaps head-on with a half full hybrid sp orbital of the beryllium to form a sigma bond.

  18. “sp2” Hybridization: All 3 Region Species

  19. Hybridization of B in BF3 Hybrid sp2 orbitals: 1 part s, 2 parts p Valence e’s Atomic B : 1s2 2s22p1

  20. FORMATION OF BF3: Each fluorine atom, 1s22s22p5, has one unshared electron in a p orbital. The half filled p orbital overlaps head-on with a half full hybrid sp2 orbital of the boron to form a sigma bond.

  21. Hybridization of C in CH4 Valence e’s Hybrid sp3orbitals: 1 part s, 3 parts p Atomic C : 1s2 2s22p2

  22. FORMATION OF CH4: Each hydrogen atom, 1s1, has one unshared electron in an s orbital. The half filled s orbital overlaps head-on with a half full hybrid sp3 orbital of the carbon to form a sigma bond.

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