Chemistry 141 Friday, December 1, 2017 Lecture 35 Chemistry 11 - Lecture 11 9/30/2009 Chemistry 141 Friday, December 1, 2017 Lecture 35 Kinetic Molecular Theory of Gases

Energy levels for 2p MOs σ*2p π*2p 2p 2p π2p σ2p σ*2s 2s 2s σ2s XA X2 XB

s-p Orbital Interactions

Energy levels for 2p MOs σ*2p σ*2p π*2p π*2p 2p 2p 2p π2p σ2p σ2p π2p XA X2 XB XA X2 XB

MO Diagrams for 2nd Period Diatomics

Heteronuclear diatomics: NO σ*2p Example: NO (5 + 6 = 11 valence e–) Electron configuration: (σ2s)2(σ*2s)2(σ2p)2(π2p)4(π*2p)1 Where is the unpaired electron? MO scheme suggests more density on N This is in agreement with the Lewis structure: π*2p 2p π2p 2p σ2p σ*2s 2s 2s σ2s N NO O N O : .

Molecular Orbital Theory Two models of bonding Hybridization Simple Hybridization of valence shell s,p, and d orbitals on one atom to form new atomic orbitals with the correct geometry Atomic orbitals on adjacent pairs of atoms overlap to form bonds Electrons are shared by only 2 atoms Molecular Orbital Theory Simple only for diatomic molecules Atomic orbitals on all atoms combine to form molecular orbitals Electrons fill molecular orbitals; bonds form when there are more e- in bonding than antibonding orbitals Electrons delocalized over molecule Doesn’t handle resonance excited states O2 paramagnetism Does handle resonance excited states O2 paramagnetism

Recall that for gases Pressure is proportional to temperature Pressure is inversely proportional to volume Can we explain these observations in terms of motions of individual gas molecules?

Principles of Kinetic Molecular Theory A gas is many small particles in constant, linear motion. The majority of the volume of a gaseous substance is empty space. Particles collide with each other and with the walls of the container. Intermolecular forces are negligible, other than collisions. Total kinetic energy remains constant, though individual particles may gain or lose energy via collisions.

Distribution of speeds

Speed vs. molecular mass

Effusion & Diffusion Effusion is the escape of gas molecules through a tiny hole into an evacuated space. Diffusion is the spread of one substance throughout a space or a second substance.

Principles of Kinetic Molecular Theory A gas is many small particles in constant, linear motion. The majority of the volume of a gaseous substance is empty space. Particles collide with each other and with the walls of the container. Intermolecular forces are negligible, other than collisions. Total kinetic energy remains constant, though individual particles may gain or lose energy via collisions.

Real Gases