Chemical bonding (VBT)

Chemical Bonding - (VBT) Energy diagram of s-s overlap of Hydrogen molecule Bond Length and Bond Energy Bond Energy: The amount of energy given off or released per mole at the time of overlapping of atomic orbitals to form a bond is termed as Bond Energy Bond Length: The equilibrium distance at which the forces of repulsion are balanced by forces of stabilization/merger between two atomic nuclei is termed as Bond Length Why does a stronger bond have a shorter bond length? Covalent Bond and Types Sigma Bond : Head-On Overlap s-s overlap Ex: H2; s-p overlap Ex: HF, HCl p-p overlap Ex: F2, Cl2 Pi Bond : Sidewise/lateral overlap During the formation of sigma bond the extent of overlapping is more and hence sigma bond is stronger than pi bond Explaining Single Bonds For molecules like hydrogen fluoride : • The 1s orbital of H overlaps with the half-filled 2p orbital of F 25 % s-character and 75% p-character Explaining Single Bonds For molecules like methane: • • the VB theory of hybrid orbitals is used to explain molecular shape carbon forms four hybrid orbitals (sp ) by combining three 2p orbitals and a 2s orbital so that four identical bonds can be created The four sp orbitals of C overlap with the s orbitals of H to form methane Mixing of s orbital with three p orbitals 33 % s-character and 67 % p-character Explaining Double Bonds For bond formation in ethene: • • • one sp orbital of each carbon overlaps to form a σ bond between the carbons two sp orbitals of each carbon overlap with the 1s orbitals of the hydrogens to form σ bonds the lobes of the 2p orbitals of each carbon overlap above and below the plane to form a pi ( π) bond The three sp orbitals of C overlap with the s orbitals of H to form ethene Mixing of s orbital with two p orbitals 50 % s-character and 50 % p-character Explaining Triple Bonds For molecules like ethyne: • • • the linear structure is explained by formation of sp hybrid orbitals for each carbon (a 2s orbital + a 2p orbital) sigma bonds form from overlap between sp of each carbon and between sp of carbons and 1s of hydrogens two pi bonds form from overlap of the two 2p orbitals of each carbon The two sp orbitals of C overlap with the s orbitals of H to form ethyne Mixing of s orbital with one p orbital ... have a shorter bond length? Covalent Bond and Types Sigma Bond : Head-On Overlap s-s overlap Ex: H2; s-p overlap Ex: HF, HCl p-p overlap Ex: F2, Cl2 Pi Bond : Sidewise/lateral overlap During the... molecules like hydrogen fluoride : • The 1s orbital of H overlaps with the half-filled 2p orbital of F 25 % s-character and 75% p-character Explaining Single Bonds For molecules like methane: • • the... the s orbitals of H to form methane Mixing of s orbital with three p orbitals 33 % s-character and 67 % p-character Explaining Double Bonds For bond formation in ethene: • • • one sp orbital