NEET Chemistry Notes: Chemical Bonds and Molecular Structure PDF

## 4. Chemical bond and Molecular Structure. ### CHEMICAL BOND It is a force of attraction between two or more atoms or ions. A stable molecule is known as a chemical bond. ### Chemical bond #### Theories of Bonding #### Bond Parameters ##### Nature * Strong * Weak Bond ##### Break * Break * Bre...

## 4. Chemical bond and Molecular Structure. ### CHEMICAL BOND It is a force of attraction between two or more atoms or ions. A stable molecule is known as a chemical bond. ### Chemical bond #### Theories of Bonding #### Bond Parameters ##### Nature * Strong * Weak Bond ##### Break * Break * Break * More energy is requried. * Less energy is required. #### • Theories of bonding ##### Subtopics * [Type of bond?] 1. Lewish Kossel Approach (Lewis dot structure) 2. VSEPR (valence shell e-pair repulsion theory) 3. VBT (Valence bond theory) - Hybridisation - Molecular Orbital Theory. (MOT) #### • Purpose of chemical bond formation. To attain Stability Due to force of attraction atoms, potential energy decreases, and stability increases. in ↑ (PE) [KJ/mol] PE=0 HOH HA HA HA HM HH → Bond length ✓✓ 435.8 Inter nudear distance Hzcg) + 435.8 kJ/mol ↓ Hcg) + Hcg) #### • Lewish octet Rule → Atoms can combine by transfer of valence electrons from one atom to another, i.e by gaining, losing, or sharing of valence electrons in order to have an octet in their valence shell. This is the octet rule. ##### Examples * **NaCl → Na+ Cl-** * **Na (11)** * 1s2 2s2 2p6 3s2 * Valence e- = 1 * Na→ 1s2 2s2 2p6 * **Cl(17)** * 1s2 2s2 2p6 3s²3p5 * Valence electron = 7 * **Cl→ 1s2 2s2 2p6 3s2 3p6.** * **MgCl2 (Magnesium chloride)** * **12Mg** * 1s2 2s2 2p6 352 * **Mg** * Valence e=2. * **17Cl** * 1s2 2s2 2p6 3s23p5 * Valence e- = 7 * **Mg (2e-loss)** * **Cl (e-gain)** * **Cl (e-gain)** * **AlCl3 Aluminum Chloride** * **13Al** * 1s2 2s2 2p6 3s23p+ * Valence e-=3 * **Al** * (3e-loss) * **17Cl** * 1s2 2s2 2p6 3s2 3p5 * Valence=e-7 * **Cl (gainte-)** * **Cl (gainte-)** * **Cl (gain te-)** #### Lewis Dot structure - Valence e- representation. Li, Be ,B ,C, (2,1) (212) (2,3) (2,4) Example:- (1) 02 , N ,O (2,5) (2,6) * :F: * (2,1) * Ne * (2,8) * 02 * :::, * 8e- * 8e * O3 * 00 * 8e- * 0=0=0 * 8e- * 8e * N2 * N≡N * Be * Bebe- * CO2 * Be * Be- * 0=C=0 * 8e- * 8e * O3 * 00 * 8e- * 0=0=0 * 8e- * 8e- #### #Covalent bond → Sharing of e- between the atoms to form a bond is known as covalent bond. * **A-A Single Covalent Bond** * **A=A Double Covalent Bond** * **A≡A Triple covalent Bond.** #### H2 → Hydrogen molecule. HOH - Single - Covalent Bond - 2e Duplet - 2e- Duplet #### Note: To write the lewis dot structure following steps are to be followed. * The total number of e- are obtained by adding the valence e- of combining atoms. * For anion, we need to add to one e- for each negative charge * For cation, we need to subtract one e- for each positive charge After, then the central atom is decided:- To decided the central atom following steps are followed. In general, the least e- negative atom occupies the central position in the molecule, ion, for example in the NH3, NF3 and CO2; nitrogen and carbon are the central atom whereas fluorine and oxygen occupies the terminal positions. -2 #### NF3 Least E-N (Central atom) F N F F Occupies the Terminal position. -2 #### [Carbonicion] -2 gaine- XOX xx 8e- XX X X x 丈 XX X e gain 8e (v) Generally, the atoms which is less in number act as central atom. Generally, central atom is the atom which can form maximum number of Bonds (which is generally equal to the number of electrons present in the valence shell of the atoms.) Atom of highest atomic number/largest atom generally act as central atom. #### Covalency NEXT →After accounting for shared pair of e-, accounting for the single bond, the remaining e- pair are either utilized for multiple bond, remaining as the lone pair. The basic requirement that needs to be satisfied is that an octet of e- is maintained. It is the total number of electron beyound can present #### Covalency of 3rd period element beyound has 1s2 2s2 2p2 vacant orbital * **5B → 1s22s22p2 3s23p1** * 1e- unpaired * 2e- paired * Mono valent * Divalent * 1st exited state * 3e unpaired * Trivalent * 4e unpaired * Tatravalent * N→ 1s2 2s2 2p3 * 1e- lose * 3e- unpaired * Trivalent * 1111 * 1e- lose * 4e- unpaired * Tatravalent * **80** 1s2 2s2 2p4 * 1111 * 1e- lose * 2e- paired * Divalent * 1114 * 1e- lose * 3e- unpaired * Trivalent * **15P** 1s2 2s2 2p6 3s23p3 3d° * 1111 * 1111 * _1_ * Groundstate * 3e- upaird→ Trivalent * Exitedastate * 5e- upaird→ Pentavale * **16S** → 1s2 2s2 2p6 3s23p4 3do 3p1 * 1111 * 1111 * 11111 * 1111 * 1111 * 2e-Divalent * 1st exited state * 4e-(Tatravalent) * 2nd exited state * 5e-(Pentavalent) * and exite state- * 1e- unpaired * Ist exited state * 1111 * 1111 * 1111 * 1111 * 1111 * Mono valent * 2nd exited state * 3e- unpaired * Trivalent. * 4e- unpaired * Pentavalent. * 3rd exited state * 1111 * 1111 * 1111 * 1111 * 1111 * 6e- unpaired * Heplavalent. #### Identify the existing and non-existing molecule / ion. * **PC15 (✔)** * **NC15 (x)** * **(Si SF6) 2- (✔)** * **(214) (✔)** * **((F6) 2-(x)** * **(AlF6) 3-(✔)** * **At (H2O) +3 (✔)** * **(BxF6)3-(x)** * **FO3 (nonexistirng)** * **ClF3 (existing)** #### Formal Charges It is excess or deficence of e- charge it appears on an atom due to excess or deficence of e- charge. Formal charge help in the selection of the lowest energy structure from a number of possible Lewies structures for a given species. Generally, the lowest energy structure is the one with the smallest formal charges on the atoms. #### Formal charge - Total no. of Valence e- in the forceatom - Total no. of non-Bondede- (lone pair - 1 x Bonded - हिनि चाहिए - हैं. = Formal charge Formal charge 0>valence e-= 8, (होने चाहिए - हैं) valence * **6-6=0** * **6-7= -1** * **6-7=-1** * **6-6=0** H C Ex: HPO -2 H #### Write the formal charge on each indicated atom. Valance of N= 5c- * **N: -1 NNN:: -1 3 -1 N3 Ng** * a) 5-6=~1 * b) 5-4=1 * c) 5-6=-1 * a) 5-6=-1 * b) 5-4=1 * c) 5-7=-2 Charge की Shifti Dandare -resonating Structure of A zicle Ion. (N31). where the structure is more steeble becacure evenly - oxyzen = 6 e-valency - N= Se-veleny * **5-5=0 * **5-4= +1 * **6-7=-1 * **5-6=4-1 * **5-4=+1 * **6-6 = 0 * **6-6=0 * **6-6-5 =+1 * **6-7 = -1 * **6-7=-1 * **5-4=1 * **6-6=0 #### #Exceptions of octacte rules. - Imcoplete octet or electron deficient compound also k/n. as Hypovalent The number of electrons surrounding the central atom is less than 8. Ex LICI, Be H2, BeCl2, AlF3, BF3, B2H6 (Diborne). -Electron rich Compounds or expanded octet, or Supper octet, an (hyper valent compound) valence e->8. - Eg: PC13 SF6 - (xe) - XeF2, - Xe F4, - Xe F6, - XeO F4. - XeF2 - Xe F6 - Odd election compounds: - Eg:- NO, NO2 - ON - 8e- - 8e- - 8e - ON - 8e- In molecules in with an odd of electron like Nit. (NO) and nitrogen dioxide and (O2), the octet rule is not for all the atom. NO2. - single e- ontdelectron. - NO - odd e- - molecule (Coordinate bond) **Competitive inhibitor** Pseudo inert gas configuration. (18e-) * ZnCl2→ Zn2+ → 3s2 3p6 3d10 => 18e- * Cucl Cut » 352 3p6 3d10 => 18e- * Agt * Cd2+ (Mg+2 Pb+4 Sn+4 **Draw Back** → It could not explain stability and shape of molecule. - +1 - +2 The total number of electron that take part in forming the bond in N₂ is. - bbonDN -> 6e- -> Bond formation - 3Bond. - (NEN) Of An odd electron molecule among the following is - NO, NO2. #### VSEPR Theory Valence shell electron pair Repultion Thec This theory provides a simple process to predict the shape of a molecule. * Lewis concept is unable to explain the shape of molecules on the covalent. * Sidgwick and Powell, 1940 proposed a simple theory based on the repulsions interactions of the election pair in the valen shell of the atom It was, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , * still develop and redefined by the -- -- _hylme and Gillespie 1937. ##### Postulate * The shapes of a molecule depends upon the valence shell election pair (Bonded election pair) non-Bonded election pc around the central pair. * The two central the valence shell --- repel one anothe → pair of election in they eou cloud are negatively charge. * This pair of electron tends to occupie such positions in the space that minimize repulsion and maxium distance between them. The valence shell takin as a sphere with the elect ron, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * - from one another on the spherical surface of, maximum disstan - in pair, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * on the spherical swtface of maximum disstan. - from one another. * A multiple bond is treated as if it is a single electron pair. - And the two or three electron pair of a multiple bond is treated as a single super pair. - Lone pair Lone pair > bond pair > bond pair bond pair bond pair. Order of repulsion. | Lone pair | Lone pair | Shape | Lone pair | Lone pair | Shape | |:---|:---|:---|:---|:---|:---| | 2 | 0| Linear | 4 | 1 | Seesaw | | 3 | 0 | Triagonal planar | 5 | 0 | T-shape | | 2| 1| Bent shape | 4 | 2 | Square planar | | 4 | 0 | Tetrahedral | 5 | 1 | Octahedral | | 3 | 1 | Trigonal pyramidal | 6 | 0 | Pentagonal bipyamidal | | |2 | Bent | 5 | 2 | Square pyramidal | | 5 | 0 | Trigonal bipyamidal | 4 | 3| Pentagonal planar | | | 1| Distorted | 6 | 1 | Distorted octahedral | | | octahedral | #### • Type: - * AB₂ ho * Linear structure * 180° * B * A * B * Centralatom * B.P→ Bond pair * Linear pair _non bonded pair e- * Linear * Bond angle = 180° * Eg- BeCl₂ * AB₃ type * Triagonal planar, shape /geometry, Bond angle = 120° * B * 120' * A * 120' * B * B * Eg BC3 * A1C13 * A1F3 * AB₂ type * Tetrahedral * 109°28' or 109.5° * A * Eg- CHU, CCL4 * B * B * B * ABS * Trigonal bipyramidal. * B * Axial (90.)6 * B * Eg:-PCIs * PF5 * B * A * B * Equitorial (120°) <3.XeO3F2 * B * AB5L。 1. Axial (90') with plane. - Shape - Square. - Equitorial(gu) Bipyramidal. - Eg:- SFG, IFG - Octahedral. - Plane * AB7L。 - go' - Axil (10). - Shape - Only B.P - Gemometery - Equitorial (5) - B.A = 72° * Type - AB₂L1 - AB3L1 / AB₂L2 - AB4L1 / AB3L2/AB2L3 - ABEY AB4L2/AB3L3/AB2L4 - ABGL/AB5L2. - Lone pair no - ABnLm #### • Type: - - Shape - Remark - AB₂L4 - V-shape, Bent Shape - Eg:- NO2, - Band angle (6 x 120') Triagonal plannar (geometry) - AB2L1 - Vshape/ Bent Shape - Eg:- H2O - Tetrahedral. - AB₂L2 - CH4 (methane) - (AB4L。 - 109.5° - H - C - H - H H Tetrahedral - NH3 (ammonia) - (AB3L₁) - H - N - - H - H Pyramidal - 107° H - (AB₂L₂) H - H -O - 104.5° H v/Bent shape. - Eq: SFU * Geometry = sea-saw * Shape = Tetragonal Bipyramidal * Lone pair are present at equitorial? * position due to B.A = 120' - AB4L1 - T-shape → Geometry = Trigonal Bipyramidal. - Eg:- ClFa, - Br F3 - IF3, - IC13. - AB2 L3 - NEET - Ey - Xe F2 - AB7L₂ - Square pyramidal shape - Gemometry = Square Bi pyramidal - Or octahedral - Eg:- CIFS/BrFs - * AB4L2 - B - B - B - A - B - B - B → Square plancar (shape) → Octahedral - eg:- XeF4. - AB6L1 - Shape: - Pentagonal Pyramidal (Distorded octahedral) - Geometry:- Deta Pentagonal Bi-pyramidal | Bond Pair | Lone Pair | Shape | Grenometry. | |:---|:---|:---|:---| | 2 | 0| Linear | Lierear | | 3 | 0 | Triangular plannar | Trigonal Planar | | 2| 1| Bent shape | Tetrahedr | | 4 | 0 | Tetrahedral | Tetrahdral | | 3 | 1 | Trigonal pyramidal | Trigonal Bipyramidal | | 5 | 0 | Triagonal bipy- | Trigonal | sea-saw | Bipyramidal | | Tshape | | 3 | 2 | Linear | | | 6 | 0 | Octahedral | Octahedral | | 5 | 1 | Square pyramidal | | | 4 | 2 | Square planar | | | 7 | 1 | Pentagonal bipyramidal | Pentagonal bipyramidal. | | | 1| Distorted octahedral | | #### Geometry v/s shape. - Geometry / Electron Pair Geometry. - Predicted using lone electron pair and bond electron pair around central atom. - Shape/molecular Geometry - Pridicted using bond electron pair around central atom - Lonepair electrons containing orbitals are ignored. - Ex 1) 4,0 shape Tetrahedral / 2) 3,1 Shape - Pyramida - 3) 3,2 shape →Tetrahedrall - →T-shape - Germometry Triagonal Bipyramidal. - Cremometry- Tetrahedr - which of following has a genometry different from other? - XeFy. - In which of the following pair two species are trigonal pryramidal. - BrO3 and xeos - In ClFu molecule, the lone pair occupy equatorial positi - Lone pair-Lone pair repulsion and tone pair bond pair repulsion, - Valence electron of Each Grop In peroidic Table. | Group | te- | | | |:---|:---|:---|:---| | Group 1 | te- | | | | Group 2 |-2e- | | | | Group 13 |-3e- | | | | Group 14 |-4e- | | | | Group 15 |-5e- | | | | Group 16 |-6e- | | | | Group 17 | -7e- | | | | Group 18 | -8e- | | | - 4Total no of electron are present in valence e-: 8e- (2n^2) - K-shell- 2e- - L-shell- 8e- - M-shell - 18e- - N-shell 32e - O-shell 50e- #### Valene Bond Theory (V.B.T) It was presented by Hitler and London to explain how a covalent bond is formed. → The main point of theory are. * To form a covalent bond overlapping occurs between half filled valence shell orbitals of the two atom. * Resulting bond accures a pair of electron with opposite spin to get stability. * Orbitals come closer to each other form the direction which their is maximum overlapping. * So, covalent bond has directional characters, extant of overlapping & Strength of chemical BDND. * Extent of overlapping depends on two factor :- @nature of orbital - Nature of overlapping - Direction - Pa.f - move ovelepping - Direction-> Less overlapping - co-axial overlapping - Co-lateral overlapping - Extent of overlapping is more. - Co-lateral overlapping, - / Side wise. #### Types of Overlapping * **S-S overlapping** - x-axis.- - internudear - axi's. - S + - S - -Bond - Dumbell Shape. - Two-s-orbital overlap (sigma) - each other along the intercellular * ''S-P overlapping'' - Inter nuclear - axis - x-axis - P-orbitals - Px, Py, Pz - Px-Orbital - S-orbital. - -Bond} - X - Y - No Bond - S+Px - No Bond * ''P-P overlaping' - y - y - Px - Px - Co-axial overlapping - (-Bond) - X - -Bond - (Px+Px - y - -Bond - -Bond - Py+ Pyy - Z - -Bond, - Co-lateral overlapping or - Sidwise overlapping - T-Bon (Pic) - Px - P2 +P2 - y - -7-Bond - -Bond - -Bond. * ''Pd-dn doverlapping'' - dxy+ Pry →IBond - y - x - dxy+ Px - xx - yorz(no-Bound) form - y - dxy - Py - y - colateral / side wise - TIBond - Sidewise overlapping - T-Bond. **dr-dn Overlapping** - x - - Bond - dxy + dxy - - T-Bond - -S-Bond - (Delta) - Degenrate orbitals - dxy - dxy - Sidwise - loverlapping, - dxy. #### VBT-Ⅱ→ Hybridiration **Important Point** →Hypothetical concept introduced by pauling and sleter. →Atomic orbitals of same atom combine to form new set of equivalent orbitals known as hybri de orbitals. this phenomenon is known as hybridiration. - The process of intermixing of atomic orbitals of equal Slightly, Different energy in the formation of new set of orbitals of equivalent energies and shape is known Hybridation. → Silent teaters of Hybridation. - The number of hybrid of orbitals is equal to the number of the atomic orbitals that get hybridised. - The hybridised orbitals are always equivalent in energy and shape. The hybrid orbitals are more effective in forming atomic whil - This hyynd orbitals are directed in space in same pretere Direction to have minimum repultion between electron pair and thus, a stable arrengement is orbtai obtained. Therefore the type of Hybridisation inclicates the gemometry of molecules. - Some Important Conditions for hyetsbridization. * The orbitals present in valence shell. (And some times penu - imate shell also) of the atom Hybridised. * The orbitals under going hybridisation should be alsnost equa energy. * Promotion of electron is not essintial for hydralisation. * It it is the orbital undergo hybridisation and not the electron. - For example: orbitals of nitrogen atom (2s²2px 2py2), Half filled stable electronic contiguation) belonging to valence shell when hybridisaded to form four Hybrid orbitalsy." - N (2s2 2px 2py P2) - { - SPx1 Py P¿ - [ - A - 1/1/1 - Ja - Sp3 Spi s po sp3 - one which has two electrons and other three have le-each it is not nesseary only half filled orbital partisipate in hybridisah In some cases even filled orbital of valence shell take part in hybridisation, - Determination of Hybridisation of an atom in a molecule or Ion. - Staric no. of an atom = no. of atom Bonded with that atom + no. of lone-pair left on that atom. - Stericno. = no. of B.P + No. of L.P (Specially-Bond) - * 77-Bond is not participatec in hybridisation. - 1-Bond is not participated in - steric Number - steric NO Hybrilisation SHAPE/Geometry Bond Angle. - 2 sp linear 180' - 3 sp2 Triangular 120 - Planar - 4 sp3 tetraheral 109.5° - 5 sp3d Triangular 9 caxial) (Pavilori) - Bi-Pyramidal 120 व - 6 sp3d2 Square Pyra go° (axil, equitori) - ractahedral - 7 spad 3 Pentagonal 72", 90° - Bi - Pyramidal. (a) caxial) - Use of orbitals * Spad hybrid (Trigonal Dipyramidal) - B - A - B - B - B - axial(dz²) - equitorical * S+Px+Py)*