BackElectron Configurations of Transition Metals & Exceptions
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Electron Configurations of Transition Metals & Exceptions
Introduction to Electron Configurations
Electron configuration describes the arrangement of electrons in an atom's orbitals. For transition metals, certain exceptions to the expected filling order occur due to stability associated with half-filled and fully-filled subshells.
Transition metals are elements found in the d-block of the periodic table (Groups 3-12).
Electron configurations are typically written using the Aufbau principle, Hund's rule, and the Pauli exclusion principle.
Condensed electron configurations use the previous noble gas as a shorthand.
Exceptions in Electron Configurations: Period 4
Starting from chromium (Z = 24), exceptions to the expected electron configurations are observed in transition metals. These exceptions are due to the extra stability of half-filled (d5) and fully-filled (d10) subshells.
Chromium (Cr, Z = 24): Expected: ; Actual:
Copper (Cu, Z = 29): Expected: ; Actual:
Other elements in this period may also show similar exceptions.
Memory Tool: Chromium (Z = 24) and copper (Z = 29) are key exceptions. To get to other column members, add 5 to 24.
Example: Condensed Electron Configuration for Ag+ (Z = 47)
Silver atom:
Ag+ ion: Remove one electron (from 5s):
Practice:
Write the condensed electron configuration for Au atom and Au+ ion.
Au atom:
Au+ ion:
Exceptions in Electron Configurations: Period 5
Additional exceptions are observed in Period 5 transition metals, especially for elements like niobium (Nb) and ruthenium (Ru). These exceptions are due to similar stability factors as in Period 4.
Niobium (Nb, Z = 41): Expected: ; Actual:
Ruthenium (Ru, Z = 44): Expected: ; Actual:
Memory Tool: In Period 5, most elements have 1 electron in 5s, except for Tc (Z = 43), which has 2 electrons in 5s.
Example: Condensed Electron Configuration for Ru (Ruthenium)
Ru atom:
Practice:
Given the electron configuration , identify the element with a +2 charge.
Element: Pd2+ (Palladium ion)
Summary Table: Common Transition Metal Electron Configuration Exceptions
Element | Expected Configuration | Actual Configuration | Reason for Exception |
|---|---|---|---|
Cr (Z = 24) | Half-filled d subshell stability | ||
Cu (Z = 29) | Fully-filled d subshell stability | ||
Nb (Z = 41) | Half-filled d subshell stability | ||
Ru (Z = 44) | Stability from electron arrangement | ||
Ag (Z = 47) | Fully-filled d subshell stability |
Additional info: These exceptions are important for understanding chemical properties, ion formation, and reactivity of transition metals. When writing electron configurations for ions, electrons are removed first from the highest principal quantum number (n), typically the s orbital before the d orbital.
