Chemistry

Linea combination of atomic orbital  molecular orbital are formed by combination of atomic orbital  if ꌏ(A)  andꌏ(B)  are the wave function of atomic orbital of two combining atomic A and B  then according  to Linea combination of atomic orbital, these two wave function can be added or can be substracted .that means there are two modes of interaction (symmetric and antisymmetric)  We know ꌏ(s)  = ꌏ(A) +ꌏ(B)  ꌏ(a) = ꌏ(A)- ꌏ(B) ꌏ(s)  and ꌏ(a)  represent wave function of bonding and antibonding moleculer orbital. the formation of moleculer orbital ꌏ(s)  and ꌏ(a)  from two atomic orbital ꌏ(A) and ꌏ(B)  is represented as Molecular orbital theory (MO)  theory: main points of mo theory are: 1.whwn atomic orbital combine they formed molecular orbital. 2.Number of molecular orbital formed is equal to number of atomic orbital combine. 3.atomic orbital are uninuclear  while molecular orbital  are polynuclear. 4.The various molecular orbital are arranged in order of in increas

shape of compounds due hybridisation 1.Shape of sncl2 (stannois chloride) Ground state Sn (50)  5s^2 5px^1 5py^1 5pz^0 since sp^2 hybridisation takes place so sncl2 molecule should be triangular or triginal planar but actually sncl2 molecule is Bent because ane position of triangle is occupied by lone pair of electron. 2 shape of ClO4(perchlorate) Ground state Cl (17)   3s^2 3px^2 3py^2 3pz^1 3d^0 excited state           3s^2 3px^1 3py^1 3pz^1   3d^3            { sp3 hybridisation }      {π bond} orbital formed π bond don't take part in hybridisation .since sp3 hybridisation take place . so ClO4 is tetrahedral. 3.Shape of ClO3^-(chlorate ion) Ground state Cl (17)  3s^2  3px^2 3py^2 3pz^1 3d^0 excited state           3s^2  3px^1 3py^1 3pz^1 3d^2           { sp3 hybridisation}    {2π bond} since sp3 hybridisation takes place .so clo3^-should be tetrahedral. but actually clo3^- is pyramidal .because one position of tetrahedral occupied by lone pair of elec

Shape of compounds due hybridisation 1.Shape of IF7 ( iodine hepta fluoride) Ground state I (53)    5s^2 5px^2 5py^2 5pz^1 5d^0 excited state            5s^1 5px^1 5py^1 5pz^1 5d^3              {     sp3d3 hybridisation          } since sp3d3 hybridisation takes place .so IF7 molecule is pentagonal bipyramidal. bond angles 72° &  90°. 2.shape of NH3(Ammonia) Ground state N (7)   1s^2 2s^2 2px^1 2py^1 2pz^1          {sp3 hybridisation} since sp3 hybridisation takes place. so NH3 molecule should be tetrahedral. but actual NH3 molecule pyramidal. because one position of tetrahedral occupied by lone pair of electron. Due to lone pair -bond pair repulsion bond angle decrease from 109°28' 3.shape of H2O(Water) Ground state (H)  1s^2 2s^2 2px^2 2py^1 2pz^1                { sp3 hybridisation} since sp3 hybridisation takes place so H2O molecule should be tetrahedral is V shaped (bent shaped)  because two positions of tetrahedral are occupied by lone pair

shapes of many compounds due hyberdisation 1.shape of BF3 (boron trifluoride) Ground state  B (5)    1s^2  2s^2  2px^1  2py^0 2pz^0 excited state     1s^2  2s^1  2px^1  2py^1  2pz^0                 { sp2 hybridisation} since sp2 hybridisation takes place. so BF3 molecule triangular with bond angle 120° triangular or trigonal planer 2.shape of CH4 (Methane) Ground state  C (5)    1s^2  2s^2  2px^1  2py^1 2pz^0 excited state     1s^2  2s^1  2px^1  2py^1  2pz^1                 { sp3  hybridisation} since sp3 hybridisation takes place. so CH4 molecule tetrahedral with bond angle 109°.28' 3. shape of PF5 (phosphorus pentafluorine) Ground state  P (15)    3s^2  3px^1  3py^1 3pz^1 3d^0 excited state           3s^2  3px^1  3py^1  3pz^1  3d^1                       { sp3d hybridisation} since sp3d hybridisation takes place. so PF5 molecule is tringonal bipyramidal. equitorial 120° axial 90° axial bond are slightly larger than equatorial bond b

Hybridisation:  the phenomenon of intermining of various orbital which differ slightly in energy to give rise to new orbital of indentical energy is called hybridisation. hybrid orbital form stronger covalent bond because they are more directional. types of hybridisation: depending upon the no.  and type of hyberdisation, hybridisation can be of sp, sp^2, sp^3, sp^3d, sp^3d^2, sp^3d^3. conditions for hybridisation: 1.orbital valence shell take part in hybridisation 2.orbital taking part in hybridisation should be of almost same energy. 3.orbital forming π bond do not take part in hybridisation. shape of compounds 1.Shape of BeF2 (beryllium dichloride) ground state    Be    (4)    1s^2 2s^2 2px 2py 2pz excited state    Be     1s^2 2s^1 2px^1 2py 2pz                      { sp             } since sp hybridisation takes place beF2 molecule is linear with bond angle 180°                      

Covalent bond: the bond which is formed by mutual sharing of electron is called covalent bond. this bond made by only non-metal by sharing. Ionic bond : the bond which is formed by permanent displacement of electron is called ionic bond. this bond made by only metal and non-metal. Factors favouring covalent bond: 1.high ionisation . 2.high electro affinity and high electronegativity. 3.high nuclear charge. 4.valence shell having 5,6,7 electron. characteristic of covalent compound: 1.melting point and boiling low: covalent compound have low melting point and boiling point because little energy is required to break weak intermolecular force. 2.Solubility: covalent compounds are generally soluble in organic solvent like benzene. 3.physical state: covalent compound can exist as gas due to the presence of weak forces. however they exist as soft solid  only when their molecules weight are high. 4.directional characteristics of covalent compound: covalent compound is

electronegativity scales and its advantages and numericals 4.Sanderson's scale of electronegativity: this scale is based upon new quantity called stability ratio=E.D/E.Di  stability ratio of an atom is defined as ratio of average electron density (E.D)  around the nucleus and it's ideal hypothetical electron density (E.Di)  which the atom would have if it work on inert atom. stability ratio=E.D/E.Di A/c to sanderson's stability ratio of an atom measure it's electronegativity X(A) (sanderson) = E.D/E.Di Electronegativity on pauling scale: X(pauling) = 0.21(X(A)sanderson ratio) +0.77 5.Mulliken zaffee electronegativity scale: Zaffee and his coworker extended the Mulliken definition and suggested that electronegativity  of an atom is different in different environment some of these factor which affect electronegativity are 1.Oxidation state:  more is the oxidation state ,more is the attraction for electron,  hence more will be the electronegativity.

Electronegativity scales: 1.Pauling scale of electronegativity: in diatomic molecule (A-B) ,the bond formed between two atoms A and  B will be intermediate between  pure Covalent (A-B)  and pure ionic character,  the bond between A and B will be  strong than bond energy increased. if bond (A-B) has been purily covalent than bond energy can be calculated as average bond energy of bond (A-A)  and bond (B-B).     that means it is equal to bond energy of bond (A-B) E(A-B)  = 1/2[ E(A-A) +E(B-B) ] however experiemental value of bond (A-B)  more than this value  because of difference in electronegativity  of A and B the difference ∆ is given by simple expression ∆ = E(A-B) - 1/2 [E(A-A) +E(B-B) ] where E(A-B)  is experimental value of bond energy. if Ҳ(A)  and  Ҳ(B) are the electronegative of elements A and B than Ҳ(A) - Ҳ(B) = 0.18√∆ for numerical ∆ = E(A-B)  -[√(E(A-A) ×E(B-B) )] Disadvantages of pauling scale of Electronegativity: main disadvantage of pauling scale is

Electronegativity :  The tendency of  an atom to attract shared pair of electron towards it side is called electronegativity. Variation of Electronegativity in group:  Electronegativity decrease from top to buttom in a group because as atomic size increase tendency to attract shared pair of electron decrease. Variation of Electronegativity in periods:  Electronegativity increase from left to right in a period because as  effective nuclear charge increase tendency  to attract shared pair of electron increase. Factors affecting electronegativity:  1.Oxidation state:  more is the oxidation state ,more is the attraction for electron,  hence more will be the electronegativity. so pb^+4 is more electronegativity than pb^+2. 2 .Hyberdistaion: Hyberdistation also affect electronegativity. sp^3  25℅ s character sp^2  33.3℅ s character sp     50℅ s character s orbital are more penetrating (s>p>d>f)  so hybrid orbital with greater s character will be more electroneg

Factors affecting electron affinity:  1.Effective nuclear charge : more is the nuclear charge, more is the attraction for extra electron, more is the amount of energy   released and hence more will be the electron affinity. 2.Atomic size: small is the size of atom, more is the attraction forextra electron and hence more will be electron affinity. 3.Electronic configuration:  elements having half filled and fully filled configuration are very stable so that have little tendency to except electron or no tendency to except extra electron. so they have very low value of electron affinity or zero electron affinity. Question /Answer 1.Electron affinity of noble gases is zero? ans because of more stability of completely filled valence shell they have no tendency to gain electron  hence electron affinity of noble gases are zero. 2.Nitrogen and phosphorus have low value of electron affinity? ans N (7)  1s^2 2s^2 2p^3 P (15)  1s^2 2s^2 2p^6 3s^2  3p^3 the electronic co

Electron affinity: electron affinity may be defined as amount of energy released  when an electron is added to neutral gaseous atom to form gaseous anion. X(g)  + 1e^- → X(g) ^- Variation of electron affinity in group : Electron afinity is decrease from top to buttom in a group. because as atmic size increase attraction for extra electron decrease. Variation of electron affinity in periods : Electron affinity is increase from left to right in a periods. because as effective nuclear charge increase attraction for extra electron increase. # electron affinity first  is always +ve. # successive electron affinity  is always -ve. O + 1e^- →O^- neutral & - ve charge molecule no large amount of energy require and both when mix it defuse .so electron affinity of first is always +ve. O^- + 1e^- →O^2- -ve & -ve charge molecule greater repulsion between than so more energy require to mix together each other so E. A of successive is always -ve. Question 1  Successive

Important question related to ionisation energy:  Question 1 Ionisation energy of gases is higher. why? ans.  because of higher stable of ns^2 np^6 configuration. or noble gases have completely filled valence shell  whuchbis more stable. so removal of electron is very difficult. hence I. E of noble gases is high. Question 2 which have more ionisation energy Oxygen & nitrogen? ans O (8)    1s^2  2s^2  2p^4 N (7)    1s^2  2s^2  2p^3 Nitrogen has exactly half filled p subshell .whuch is more stable as a result removal electron becomes difficult. hence I. E of nitrogen is more than oxygen. hence peaks show half filled & completely filled subshell of atom .which  required more energy for removal of electron .hence I. E is more Question 3 First I. E of aluminum is less than magnesium. why? ans Al (13) 1s^2  2s^2  2p^6  3s^2 3p^1 Mg (12) 1s^2  2s^2  2p^6  3s^2 in aluminum we have to remove electron from 3p orbital  which required comparatively le

Factors affecting Ionisation energy : 1.  Effective nuclear charge : More is the effective nuclear charge ,more will be the attraction for valence electron, more energy is required to remove electron and hence more will be the    I. E. 2. Size of atom :  smaller is the size of atom more will be the attraction for valence electron more energy is required to remove electron and hence more will be I. E . 3.Screening effect of inner electrons:   the electron present between the nucleus and valence shell, at as screen this is called screening effect, more is the screening effect lesser will be the I. E. 4.Removal of s and p electron :  since p electron are away as compare to s electron condition of same shell .so p electron can be removal more easily than s electron. 5. Electronic configuration :  certain electronic configuration represent more stable arrangement for eg . exactly half filled and completely filled configuration are more stable.  so more energy is required to remov

Ionisation enthalpy(energy):  Ionisation enthalpy may ne defined as amount of energy required to remove most loosely bound electron from an isolated gaseous atom to from gaseous cation. eg. solid→liquid→gas→M(g) -1e^- →M(g) ^+ heat not require      gas atom   gaseous cation Variation of ionisation energy in a group:   Ionisation energy decrease from top to button ina group because size of the atom increase. attraction between nucleus and valence electron decrease. Variation of ionisation energy in a period : Ionisation energy increase from left to right in a period because as effective nuclear charge increase .attractive between nucleus and valence electron increase so Ionisation energy is increase in period. Successive ionisation energy: After the removable of first electron it is possible to remove 2nd, 3rd,  and even more electron .Amout of energy required to remove successive or subsequent electron are known as successive ionisation energy. I. E(3) >I.E(

Factors determining size:  1 Number of shell:  more are the no.  of shells bigger is the size of atomic. 2 Number of protons:  if no.  of shells are same, more are the no.  of protons, smaller in size of atom. 3 Number of electron:  if the no.  of shells and no.  of protons are same, more are the no.  of electron bigger is the size of atom. Question & Answer Question 1 Radii of action is smaller than corresponding atom? ans:  cation is formed by loss of electron. magnitude of nuclear charge remain same .but no. of electron is decrease as a result effective nuclear charge increase so electron are more attracted by nucleus. this cause decrease in size hence cations are smaller than corresponding atom for eg.  Na^+1<Na        Al^+1<Al   etc Question  2 Radii of anion is bigger than corresponding atom? ans: anion is formed by gain of electron. magnitude of nuclear charge remains same but no.  of  electron is increase as  a result of effectiv

Atomic properties and periodic properties Atomic radii:  Distance between nucleus and valence shell called atomic radii # atomic radii increase from top to button in a group because no.  of shells increase. #Atomic radii decrease from left to right in a period because effective nuclear charge increase between valence and nucleus. Covalent radii:  covalent radii may be defined as one half of the distance between nucleus of two covalently atomic. Vanderwaal radii:  one half of the distance between the nucleus of two atomic non bonded atoms of some elements. # vanderwaal radii is always greater than covalent radii.