1Chem 101Fall 2004Atomic Structure: Chapter 5Chem 101Fall 2004Chapter OutlineThe Electronic Structures of Atoms• Electromagnetic radiation• The Photoelectric Effect• Atomic Spectra and the Bohr Atom• The Wave Nature of the Electron• The Quantum Mechanical Picture of the Atom• Quantum NumbersChem 101Fall 2004Chapter OutlineThe Electronic Structures of Atoms• Atomic Orbitals• Electron Configurations• Paramagnetism and Diamagnetism• The Periodic Table and Electron Configurations2Chem 101Fall 2004Quantum Mechanical Picture of theAtom• Werner Heisenberg in 1927 developed the conceptof the Uncertainty Principle.• It is impossible to determine simultaneously boththe position and momentum of an electron (or anyother small particle).Chem 101Fall 2004Quantum Mechanical Picture of theAtom• Consequently, we must must speak of theelectrons’ position about the atom in terms ofprobability functions.• These probability functions are represented asorbitals in quantum mechanics.Chem 101Fall 2004Postulates of Quantum Mechanics• Atoms and molecules can exist only in certainenergy states. In each energy state, the atom ormolecule has a definite energy. When an atom ormolecule changes its energy state, it must emit orabsorb just enough energy to bring it to the newenergy state (the quantum condition).3Chem 101Fall 2004Postulates of Quantum Mechanics• Atoms or molecules emit or absorb radiation(light) as they change their energies. Thefrequency of the light emitted or absorbed isrelated to the energy change by a simple equation.λνhch E ==Chem 101Fall 2004Postulates of Quantum Mechanics• The allowed energy states of atoms and moleculescan be described by sets of numbers calledquantum numbers.• Quantum numbers are the solutions of theSchrodinger, Heisenberg & Dirac equations.• Four quantum numbers are necessary to describeenergy states of electrons in atoms.Ψ=Ψ+∂Ψ∂+∂Ψ∂+∂Ψ∂− EV8bequationdinger oSchr22222222..zyxmπChem 101Fall 2004Quantum Numbers• Quantum numbers are called n, l, and ml are alsocalled the “principal,” “azimuthal,” and “magnetic”quantum numbers.• A set of these 3 defines an orbital.•An orbital is the wave representation of an electron inan atom.4Chem 101Fall 2004Quantum Numbers• The principal quantum number has the symbol – n.n = 1, 2, 3, 4, ...... “shells”n = K, L, M, N, ......The electron’s energy depends principally on n .Chem 101Fall 2004Quantum Numbers• The angular momentum quantum number has thesymbol = 0, 1, 2, 3, 4, 5, .......(n-1)s, p, d, f, g, h, .......(n-1) tells us the shape of the orbitals.• These orbitals are the volume around the atom that theelectrons occupy 90-95% of the time.Chem 101Fall 2004Quantum Numbers• The symbol for the magnetic quantum number is mm • If = 0 (or an s orbital), then m0.• Notice that there is only 1 value of mThis implies that there is one s orbital per n value. n ≥ 1•If = 1 (or a p orbital), then m-1,0,+1.• There are 3 values of mThus there are three p orbitals per n value. n ≥ 25Chem 101Fall 2004Quantum Numbers•If = 2 (or a d orbital), then m-2,-1,0,+1,+2.• There are 5 values of mThus there are five d orbitals per n value. n ≥ 3•If = 3 (or an f orbital), then m-3,-2,-1,0,+1,+2,+3.• There are 7 values of mThus there are seven f orbitals per n value, n• Theoretically, this series continues on to g,h,i, etc.orbitals.• Practically speaking atoms that have been discovered ormade up to this point in time only have electrons in s, p, d,or f orbitals in their ground state configurations.Chem 101Fall 2004Quantum Numbers• The last quantum number is the spin quantum numberwhich has the symbol ms.• The spin quantum number only has two possiblevalues.•ms = +1/2 or -1/2•ms = ± 1/2• This quantum number tells us the spin and orientationof the magnetic field of the electrons.• Wolfgang Pauli in 1925 discovered the ExclusionPrinciple.• No two electrons in an atom can have the same set of 4quantum numbers.Chem 101Fall 2004Quantum Numbers• The last quantum number is the spin quantum numberwhich has the symbol ms.• The spin quantum number only has two possiblevalues.•ms = +1/2 or -1/2•ms = ± 1/2• This quantum number tells us the spin and orientationof the magnetic field of the electrons.• Wolfgang Pauli in 1925 discovered the ExclusionPrinciple.• No two electrons in an atom can have the same set of 4quantum numbers.6Chem 101Fall 2004Quantum Numbers: Possible Combinationsnl ml# oforbitalstype oforbitals10 0 11s2010-1,0,+1132s2p30120-1,0,+1-2,-1, 0,+1,+21353s3p3dChem 101Fall 2004Atomic Orbitals• Atomic orbitals are regions of space where theprobability of finding an electron about an atom ishighest.• s-orbital properties:• There is one s orbital per n level• = 0 1 value of mChem 101Fall 2004Distance from the nucleus,rProbabilityAtomic Orbitals: s-Orbitals• s-orbitals are spherically symmetric.Distance from nucleus,rElectron Probability2s Orbital1s Orbital7Chem 101Fall 2004Distance from the nucleus,rProbabilityAtomic Orbitals: s-Orbitals• s-orbitals are spherically symmetric.2s OrbitalOrbital Density Electron ContourChem 101Fall 2004Atomic Orbitals: p-Orbitals• p-orbital properties:•The first p orbitals appear in the n = 2 shell.• p-orbitals are peanut or dumbbell shaped volumes.• They are directed along the axes of a Cartesiancoordinate system.• There are 3 p-orbitals per n level.• The three orbitals are named px, py, pz.• They have an = 1.•m-1,0,+1 3 values of mChem 101Fall 2004Atomic Orbitals: p-Orbitals• p-orbitals are peanut or dumbbell shaped.8Chem 101Fall 2004Atomic Orbitals: d-Orbitals• d-orbital properties:•The first d orbitals appear in the n = 3 shell.• The five d-orbitals have two different shapes:• 4 are clover leaf shaped.• 1 is peanut shaped with a doughnut around it.• The orbitals lie directly on the Cartesian axes or arerotated 45o from the axes.• There are 5 d-orbitals per n level.• The five orbitals are named• They have an = 2. m =
View Full Document