CHM 101 1st Edition Lecture 17Lecture 16 Overview1. Electron Spin2. Pauli Exclusion Principle3. Energy Levels4. Aufbau Principle5. Electron ConfigurationsLecture 17 OverviewI. Core Electrons and Outer Shell ElectronsII. Valence ElectronsIII. Electron Configurations continuedChapter 6 Continued- Core electrons have the lowest energy and are the closet to the nucleus - Core electrons do not participate in bonding- Na : 1s22s22p63s1o Highlighted: core electronso 3s1: outer shell electrono Na: (Ne) 3s1- Outer shell electrons have the biggest energy and are farthest from the nucleus. These include valence electrons which are the electrons involved in bonding- Elements in the same group of the periodic table have similar electron configurations for their valence electrons - Alkali metals o Na : (Ne) 3s1o K : (Ar) 4s1- Halogenso F : (He) 2s22p5o Cl : (Ne) 3s23p5- How many valence electrons does Ca have?o Ca : (Ar) 4s2o 2 valence electrons- For main group elements electrons in a filled d-shell or f-shell are not valence electronso Br : (Ar) 4s23d104p5o 7 valence electrons- Some elements appear to violate the rule of the electron configuration due to the closeness of some orbitals in energy- Exceptions:o Cr: (Ar) 4s13d5o The outer electrons exactly fill half of the 4s and 3d subshellso Cu : (Ar) 4s13d10o Outer electrons exactly fill half 4s shell and completely fill 3d shell- Metals tend to lose electrons to form cations- Nonmetals tend to gain electrons to form anions - Atoms tend to form ions by losing or gaining electrons to achieve an electron configuration of the closest noble gas- Ca: (Ar) 4s2- Ca2+: (Ar)- Cl: (Ne) 3s23p5- Cl- : (Ar)- When more than one type of atom or ion has an identical electron configuration these atoms and ions are said to be isoelectronico Aro Cl-o Ca2+o K+o S2- All of these elements have the electron configuration of 1s22s22p63s23p6- When a transition metal forms a cation it will lose the electrons in the shell with the highest values of n first o Fe : 1s22s22p63s23p64s23d6o Fe2+: 1s22s22p63s23p63d6o Fe3+:
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