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Quantum mechanics: describes electron energies and locations by a wave equation Wave function are solutions of wave equation Each Wave function is an orbital , y A plot of y 2 describes where electron most likely to be Electron cloud has no specific boundary so we show most probable area ORBITAL

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There is no way of determining the exact location of an electron within an atom. There is a definite 3 dimensional area around the nucleus within which an electron is most likely to be found. ORBITAL

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P-ORBITALS In each shell there are three mutually perpendicular p orbitals, px.py and pz of equal energy The lobes of a p orbital are separated by a region of zero electron density ,a node

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Covalent bond forms when two atoms approach each other closely so that a singly occupied orbital on one atom overlaps a singly occupied orbital on the other atom There are two ways orbitals can overlap to form bonds between atoms. BOND FORMATION

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Sigma () Bonds –Formed by s-s ,s-p and axial overlap of p-p orbitals Sigma bonds are characterized by Head-to-head overlap. Cylindrical symmetry of electron density about the internuclear axis. s BOND

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Pi bonds are characterized by Side-to-side or lateral, or unsymmetrical overlap of atomic orbitals Electron density above and below the internuclear axis. () Pi () Bonds

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bond formation Overlapping of atomic orbitals s and p bond formation

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Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridizationprocess. Mix at least 2 nonequivalent atomic orbitals (e.g. sand p).Hybrid orbitals have very different shapefrom original atomic orbitals. Hybridization

Orbital Changes- Excitation : 

Orbital Changes- Excitation

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BONDING IN METHANE Sp3 HYBRIDIZATION ground state excited state hybridized state CARBON The formation of four sp3 hybrid orbitals by combination of an atomic s orbital with three atomic p orbitals. Each sp3 hybrid orbital has two lobes, one of which is larger than the other. The four large lobes are oriented toward the corners of a tetrahedron at angles of 109.5°. The carbon atom is sp3 hybridized to obtain tetrahedral geometry

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17 s + 3 p 4 sp3 orbitals

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sp3 hybridized orbital 4 orbitals All the same shape, size and energy Arranged in a tetrahedral conformation Gives minimum repulsion between orbitals. Angle of 109º from each other Can form bonds by overlapping with orbitals of other atoms.

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The bonding in methane. Each of the four C-H bonds results from head-on (s) overlap of a singly occupied carbon sp3 hybrid orbital with a singly occupied hydrogen 1s orbital. Sigma bonds are formed by head-to-head overlap between the hydrogen s orbital and a singly occupied sp3 hybrid orbital of carbon. BONDING IN METHANE

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In Ethane the two carbon atoms are in the Sp3 hybridized state Out of four Sp3-hybrid orbitals one Sp3-hybrid orbital of one C-atom overlaps with one s-orbital of  H-atom to produce three sigma bond and the last overlaps with one Sp3-orbital of other C-atom axially to   produce a sigma bond between two C-atoms. C2H6 CH3CH3 STRUCTURE OF ETHANE

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BONDING IN AMMONIA In the case of ammonia, the three 2p orbitals of the nitrogen atom are combined with one 2s orbital to form four sp3 hybrid orbitals. The non-bonded electron pair will occupy a hybrid orbital..

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The bonding geometry will not be tetrahedral when the valence shell of the central atom contains nonbonding electrons, however. The reason is that the nonbonding electrons are also in orbitals that occupy space and repel the other orbitals. This means that in figuring the coordination number around the central atom, we must count both the bonded atoms and the nonbonding pairs. BONDING IN AMMONIA

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Ammonia assumes a pyramidal shape. More precisely, the shape is that of a trigonal pyramid (i.e., a pyramid having a triangular base). The fourth orbital containing the non-bonding electrons pushes the bonding orbitals together slightly, making the H–N–H bond angles about 107°. BONDING IN AMMONIA

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BONDING IN AMMONIUM ION The hybridization of N in Ammonium ion is sp3.In the formation of Ammonium ion the four hybrid orbitals contain bond pair therefore the shape is here also tetrahedral

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BONDING IN WATER Two of the coordination positions are occupied by the shared electron-pairs that constitute the O–H bonds, and the other two by the non-bonding pairs. Thus although the oxygen atom is tetrahedrally coordinated, the bonding geometry (shape) of the H2O molecule is described as bent

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Thus in H2O, the two nonbonding orbitals push the bonding orbitals closer together, making the H–O–H angle 104.5° instead of the tetrahedral angle of 109.5°.

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