Chapter 6 Electronic Structure of Atoms KEY QUESTIONS THE BIG PICTURE What is the structure of an atom What are the properties of atoms Remember structure affects function Where are the electrons located What is the energy of an electron By the end of Lecture 6 you should know wavelength and frequency of light dual nature of light electronic transitions and line spectra Bohr model Matter acts as waves Heisenberg Uncertainty Principle Electronic transitions of orbitals Quantum numbers n m ms Orbitals their shapes and energies Orbitals and atoms with many electrons Spin quantum number ms Pauli Exclusion Principle and Hunds Rule Electron Configurations using the periodic table CH110 FA10 SAS 1 Concept Check Understanding electromagnetic energy led to quantum theory it explains what we observe which led to atomic structure and predicts electron configurations and explains periodic trends of the elements CH110 FA10 SAS 2 So electrons are found in Orbitals 1 Principal quantum number n 2 Azimuthal quantum number 3 Magnetic quantum number m Symbols used for the quantum numbers l value subshell name Two electrons fit in each orbital more on this next time of electrons Some Examples n 1 n 2 n 2 n 3 l 0 l 0 l 1 l 0 ml 0 ml 0 ml 1 0 1 ml 0 CH110 FA10 SAS 3 Classification of Orbitals n size shape ml Orbitals in Orbitals in direction subshell shell 1 2 3 4 Orbitals are defined by a set of n m There are n2 orbitals in the nth shell CH110 FA10 SAS 4 Practice Problem Which of the following shows the correct n and m quantum numbers for an electron in a 3p subshell A B C D E n 3 n 3 n 3 n 3 n 3 0 2 1 1 2 m 0 m 0 m 0 m 2 m 1 CH110 FA10 SAS 5 Shapes of the Orbitals Determined by the 2 of finding an electron at a certain distance r from the nucleus Example s orbitals electron density or probability 2 2 1s 0 r at nucleus r 0 Size of s orbital as n increases 2s is than 1s Shape symmetry meaning CH110 FA10 SAS 6 Hydrogen Atom in the Ground State Where is the Electron We know precisely where e is Dense dots indicate where we are to find eCH110 FA10 SAS 7 Shapes of the S Orbitals S Orbitals 0 Size determined by Shape is CH110 FA10 SAS 8 Shapes of the P Orbitals The first p orbitals 1 are found when n 2 n 2 same 1 m 1 0 1 different Two lobes with in between Energies of the three orbitals are meaning CH110 FA10 SAS 9 Shapes of the D Orbitals The first d orbitals 2 are found when n 3 n 3 2 m same CH110 FA10 SAS 10 Practice Problems 1 Which quantum numbers are needed to define the subshell A n only B n and C only D m only E n and m 2 Which picture or pictures represent an orbital with a value of 2 1 2 3 4 5 A B C D E 1 3 4 2 and 5 1 and 3 CH110 FA10 SAS 11 Orbitals Summary Orbitals Allowed for electrons in atoms all atoms not just hydrogen Describes of electrons in these energy states Orbital name number of orbitals shape s p d f Quantum Numbers defines n principal azimuthal m magnetic CH110 FA10 SAS provides 12 Energies of Orbitals 1 One electron cases E n2 not dependent on or m Two or more electrons E depends on but not Therefore E2s E2p E3s E3p E3d Value of n determines shell Same n and means same and Same subshell means same CH110 FA10 SAS 13 Energies of Orbitals The Hydrogen Atom CH110 FA10 SAS 14 Energies of Orbitals Many Electron Atoms Typical Orbital Energy Sequence 1st 1s 2s 3s 4s 5s 6s CH110 FA10 SAS 2nd 3rd 2p 3p 4p 5p 6p 4th 5th 3d 4d 4f 5d 5f 6d 6th 15 Why do the Energies Differ Qualitatively Forces act on Electrons in Orbitals Electrons in outer orbitals see nucleus and also the electrons electrons in a lower energy s and p orbitals have different which impacts the average from the nucleus s orbital has density at the nucleus but p d and f orbitals have a there s electrons see more of Z the have lower and are more p electrons see less of Z have higher are less CH110 FA10 SAS 16 Why do the Energies Differ Quantitatively Recall orbital energy is the energy released when an electron goes into the empty orbital negative or needed to remove it positive H atom Energy does not depend on or m 1 E n RH n 2 1 e atom with nuclear charge Z He Li 2 Z E n RH n 2 Multi electron atom where Zeff effective nuclear charge reduced by screening Z eff E n RH n CH110 FA10 SAS 2 17 What You Should Know Orbitals Describe the probability density for finding an electron in a given region of space why can t we know it exactly The surfaces we draw to represent orbitals enclose 90 of the electron density another term for the probability density Orbitals specify the energy of the electron differ in E some degenerate increase in energy and size as average distance from nucleus increases Characterized by 3 quantum numbers CH110 FA10 SAS 18 What You Should Know Quantum Numbers n must be a positive integer and describes the size of the orbital and its average distance from the nucleus is an integer from 0 to n 1 defines shape What is the common one letter name attached to 0 1 2 3 m is an integer from to and defines the orientation of the orbital in space What is a shell What is a subshell CH110 FA10 SAS 19 What You Should Know Orbital Shapes s orbitals are radially spherically symmetric and increase in size as n increases One s orbital per shell p orbitals have dumbell shape but differ in orientations There are 3 degenerate p orbitals per shell d orbitals have four leaf clover shape plus one dumbell with a taurus and differ in orrientation There are 5 degenerate d orbitals per shell f orbitals exist but we aren t really covering them in much detail for now CH110 FA10 SAS 20