Chemical Bonding II PDF

CHEMICAL BONDING II Dr. Alya A. Arabi Department of Biochemistry College of Medicine and Health Sciences Excitation Excitation is the addition of a discrete amount of energy (called excitation energy) to a system. The system goes from ground state (lowest in energy) to an excited state (higher in...

CHEMICAL BONDING II Dr. Alya A. Arabi Department of Biochemistry College of Medicine and Health Sciences Excitation Excitation is the addition of a discrete amount of energy (called excitation energy) to a system. The system goes from ground state (lowest in energy) to an excited state (higher in energy). https://imagine.gsfc.nasa.gov/educators/les sons/xray_spectra/background-atoms.html Excitation of a carbon atom 2p _ _ _ 2s _ 1s _ Carbon (ground state) 2p _ _ _ excitation 2s _ 1s _ Carbon (excited state) Hybridization: hybrid orbitals There are three types: sp3 (C with only single/sigma bonds) sp2 (C with double bond) sp (C with triple bond) Hybridization: hybrid orbitals https://www.chemistrysteps.com/how-to-quickly-determinesp3-sp2-and-sp-hybridization/ https://socratic.org/questions/what-are-sp-sp2-sp3-orbitals Sp3 Hybridization https://qsstudy.com/chemistry/point-conditions-hybridization sp3 hybridization It occurs when the s orbital combines with the p orbitals to give four new hybrid orbitals called sp3 orbitals. three 2p hybridization sp3 2s Orbitals in a free C atom Orbitals in C in the CH4 molecule sp2 hybridization It occurs when the s orbital combines with two p orbitals to give three new hybrid orbitals called sp2 orbitals. The remaining p orbital is unhybridized. 2p hybridization 2p sp2 2s Orbitals in a free C atom Orbitals in the sp2 hybridized C sp hybridization It occurs when the s orbital combines with one p orbital to give two new hybrid orbitals called sp orbitals. The remaining two p orbitals are unhybridized. 2p hybridization 2p sp 2s Orbitals in a free C atom Orbitals in the sp hybridized C Summary Hybridi zation Number Shape of of Hybrids Hybrids Orbital Interactions Bonding sp3 4 tetrahedral 4 sigma 4 single bonds sp2 3 trigonal planar 3 sigma plus 1 pi 2 single bonds plus 1 double bond sp 2 linear 2 sigma plus 2 pi 1 single bond plus 1 triple bond or 2 double bonds Different electronic configurations give different geometrical structures GRAPHITE sp2 hybridization MIXED sp/sp2/sp3, DEFECTS, AMORPHOUS DIAMOND sp3 hybridization Delocalized bonds When more than two adjacent atoms have available p orbitals for pi-bond formation, the overlapping can extend across all the p orbitals to form what is known as a delocalized bond. Delocalization increases the stability of molecules and is important in molecules containing C-atoms linked by double bonds. Sigma-bonds are localized bonds because the bonding electrons are between the two bonded atoms. Delocalized bonds py py py py py py ..C = C – C = C – C … py py py py py py .. C - C = C - C = C … Aromatic compounds Aromatic compounds are molecules that conjugate double bonds in a ring structure. Example: Benzene (C6H6) Each carbon has three sp2 orbitals to form three sigma bonds and one p orbital to form a pi-bond. Aromatic compounds (cont) The six p orbitals of the molecule can overlap to form delocalized bonds all around the benzene ring. C-C bonds are neither single nor double bonds. py orbital Theory of Resonance For a molecule, when two or more structures can be drawn, that differ only in the distribution of electrons, the actual structure is a resonance hybrid of all of them. Resonance hybrid has lower energy level and is more stable than either of the two structures. Benzene (C6H6) Crystal lattice Crystal lattice is a geometric structure formed by periodic arrays of atoms and is present in most of the solids. The existence of the crystal lattice implies a degree of symmetry in the arrangement of the lattice. Examples: NaCl Diamonds Graphite Crystal lattice kaffee.50webs.com/Science/activities/Chem NaCl Crystal lattice www.e-education.psu.edu Graphite Crystal lattice Diamonds Crystal lattice Quartz Electrolytes Electrolytes are compounds that ionize in water to produce aqueous solutions that conduct an electric current. They are extremely important in the body. Kidneys work to keep electrolytes concentration in blood constant despite changes in the body. In an electric field: • Positively charged ions (cations) move to the negative electrode (cathode). • Negatively charged ions (anions) move to the positive electrode (anode). https://courses.lumenlearning.com/chemistryformajors/chapter/electr olytes/ https://calfsessions.com/2011/02/electrolytes-dissociation-of-strong-ions/ Functions of covalent bonds in biological systems ➢ They join together the atoms in molecules such as carbohydrates, lipids, proteins and nucleic acids. ➢ They join together molecules (carbohydrates, lipids, etc.) to produce the basic structures of the body. Example: Collagen molecules to form tendons and ligaments. ➢ They provide the energy that drives all energy requiring processes in the body.