Atomic Theory Lecture 4 PDF

PL1001 Pharmaceutical Chemistry ATOMIC THEORY Lecture 4 Dr Alberto Di Salvo Assigning Electrons to Subshells n + l rule (Madelung’s rule) Where: n = principal quantum number l = angular quantum n...

PL1001 Pharmaceutical Chemistry ATOMIC THEORY Lecture 4 Dr Alberto Di Salvo Assigning Electrons to Subshells n + l rule (Madelung’s rule) Where: n = principal quantum number l = angular quantum number Erwin Madelung  Assigning Electrons to Subshells In H atom all subshells of same n have same energy. In many-electron atoms: a) subshells increase in energy as value of n + l increases. b) for subshells of same n + l, subshell with lower n is lower in energy. Electrons are allocated to atomic orbitals in order of increasing energetic content. This constitutes the electron filling order (often referred to as Aufbau principle) employed in the identification of the ground state electron configuration of most elements (some exceptions will be identified). Electron Filling Order (Aufbau diagram) Writing Atomic Electron Configurations List of populated atomic orbitals 1 no. of 1s electrons value of l value of n ORBITAL ORBITAL BOXBOXNOTATION NOTATION for forHe, He, atomic atomic number number== 22 Arrows Arrows 22 11 ss depict depict electron electron 1s spin spin 1s Electron Configurations and the Periodic Table  Lithium Lithium Group 1A (IUPAC 1) Atomic number = 3 1s22s1 3 total electrons 3p 3s 2p 2s 1s  Beryllium Beryllium Group 2A (IUPAC 2) Atomic number = 4 1s22s2 4 total 3p electrons 3s 2p 2s 1s  Boron Boron Group 3A (IUPAC 13) Atomic number = 5 1s2 2s2 2p1 3p 5 total electrons 3s 2p 2s 1s  Carbon Carbon Group 4A (IUPAC 14) Atomic number = 6 1s2 2s2 2p2 6 total electrons 3p 3s Here we see for the first time HUND’S RULE. When placing 2p electrons in a set of orbitals 2s having the same energy, we place them singly as long as 1s possible.  Nitrogen Nitrogen Group 5A (IUPAC 15) Atomic number = 7 1s2 2s2 2p3 3p 7 total electrons 3s 2p 2s 1s  Oxygen Oxygen Group 6A (IUPAC 16) Atomic number = 8 1s2 2s2 2p4 3p 8 total electrons 3s 2p 2s 1s  Fluorine Fluorine Group 7A (IUPAC 17) Atomic number = 9 1s2 2s2 2p5 3p 9 total electrons 3s 2p 2s 1s  Neon Neon Group 8A (IUPAC 18) Atomic number = 10 1s2 2s2 2p6 10 total electrons 3p 3s Note that we have 2p reached the end of the 2s 2nd period, and the 2nd shell is full! 1s  Sodium Group 1A (IUPAC 1) Atomic number = 11 1s2 2s2 2p6 3s1 or “neon core” + 3s1 [Ne] 3s1 (uses rare gas notation) Note that we have begun a new period. All Group 1A elements have [core]ns1 configurations.  Aluminum Group 3A (IUPAC 13) Atomic number = 13 1s2 2s2 2p6 3s2 3p1 [Ne] 3s2 3p1 3p All Group 3A elements have [core] 3s ns2 np1 configurations where n is 2p the period number. 2s 1s  Phosphorus Phosphorus Yellow P Group 5A (IUPAC 15) Red P Atomic number = 15 1s2 2s2 2p6 3s2 3p3 [Ne] 3s2 3p3 3p All Group 5A elements have 3s [core ] ns2 np3 configurations 2p where n is the period number. 2s 1s  Calcium Calcium Group 2A (IUPAC 2) Atomic number = 20 1s2 2s2 2p6 3s2 3p6 4s2 [Ar] 4s2 All Group 2A elements have [core]ns2 configurations where n is the period number.  Transition Transition Metals Metals All 4th period elements have the configuration [argon] nsx (n - 1)dy and so are d-block elements. Chromium Iron Copper Transition Element Configurations 3d 3d orbitals orbitals used used for for Sc-Zn Sc-Zn (IUPAC (IUPAC 3-12) 3-12)  Lanthanides Lanthanides and and Actinides Actinides All these elements have the configuration [core] nsx (n - 1)dy (n - 2)fz and so are f-block elements. Uranium Cerium [Rn] 7s2 6d1 5f3 [Xe] 6s2 5d1 4f1 Lanthanide Element Configurations 4f 4f orbitals orbitals used used for for La La -- Lu Lu and and 5f 5f for for Ac Ac -- Lr Lr  Ion Ion Configurations Configurations To form cations from elements remove 1 or more e- from subshell of highest n [or highest (n + l)]. P [Ne] 3s2 3p3 - 3e- = P3+ [Ne] 3s2 3p0 3p 3p 3s 3s 2p 2p 2s 2s 1s 1s  Ion Ion Configurations Configurations For transition metals, remove ns electrons and then (n - 1) electrons. Fe [Ar] 4s2 3d6 loses 2 electrons Fe2+ [Ar] 4s0 3d6 Fe Fe 2+ 4s 4s 3d 3d To form cations, always Fe 3+ remove electrons of highest n value first! 4s 3d  Ion Ion Configurations Configurations How do we know the configurations of ions? Determine the magnetic properties of ions. Sample of Fe2O3 Sample of Fe2O3 with strong magnet  Ion Ion Configurations Configurations How do we know the configurations of ions? Determine the magnetic properties of ions. Ions with UNPAIRED ELECTRONS are PARAMAGNETIC. Without unpaired electrons DIAMAGNETIC. Fe3+ ions in Fe2O3 have 5 unpaired electrons and make the sample paramagnetic.