Transcript Chapter 8
Chapter 8: Electron configurations and periodicity Chemistry 1061: Principles of Chemistry I Andy Aspaas, Instructor Electron spin and configurations • Electrons may have only one of two possible spins – Quantum number ms = +1/2 or -1/2 – Similar to poles of a magnet • Electron configuration: distribution of electrons among available subshells – Notation lists one subshell after another, with number of electrons in each given in superscript – Ex. 1s22s1 means 2 electrons in 1s and 1 electron in 2s • Orbital diagram: drawing of orbitals and their occupations – Electrons indicated by arrows, either up or down indicates spin Orbital occupancy • Pauli exclusion principle: no 2 electrons in the same atom may have the same 4 quantum numbers – Each orbital may contain two electrons, but they must be opposite spin - same-spin pair in an orbital is forbidden • Each subshell can hold twice as many electrons as orbitals in the subshell Subshell occupancies Subshell Number or orbitals Maximum number of electrons s (l = 0) 1 2 p (l = 1) 3 6 d (l = 2) 5 10 f (l = 3) 7 14 Filling orbitals • Every atom has an infinite number of electron configrations, but the ground state (stablest) electron configuration can be predicted • Aufbau principle: electron configurations can be predicted by successively filling subshells with electrons in a specific order • # electrons in a neutral atom = atomic number Using the periodic table to fill orbitals • Use the row number to determine n for s and p sublevels • Section of the periodic table corresponds with the subshell that’s added – First two groups: s – Last 6 groups: p – Transition metals: d – Inner transition metals: f Available subshells • • • • • • • 1s 2s, 2p 3s, 3p, 3d 4s, 4p, 4d, 4f 5s, 5p, 5d, 5f 6s, 6p, 6d, 6f 7s, 7p, 7d, 7f • These subshells are allowed based on allowed quantum numbers • But, they are filled based on the order they appear in the periodic table • 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 etc Writing electron configurations • Just follow the periodic table from the start, adding electrons in the appropriate sublevel • Electron configurations can be abbreviated using a noble-gas core (in brackets) – Ex. Ca = 1s22s22p63s23p64s2 or just [Ar]4s2 Electron addition to subshells • Hund’s rule: lowest energy arrangement of electrons in a subshell is obtained by first putting in as many same-spin electrons as possible before pairs are made • Oxygen: 1s22s22p4 therefore has 2 unpaired electrons in the 2p subshell – Any atom with unpaired electrons is paramagnetic (attracted to a magnetic field due to unpaired electrons)