IB DP Chemistry: HL复习笔记13.1.1 Transition Elements

• Transition metals are elements with an incomplete d-subshell or that can form at least one stable cation with an incomplete d-subshell
• This definition distinguishes them from d-block elements, because scandium and zinc do not fit the definition
  • Scandium only forms the ion Sc³⁺, configuration [Ar] 3d⁰
  • Zinc only forms the ion Zn²⁺, configuration [Ar] 3d¹⁰
• The elements of the first transition series are therefore titanium to copper

The transition elements and the d-block elements

Electron Configuration

• The full electronic configuration of the first d-series transition metals is shown in the table below
• Following the [popover id="J63HVOTKZm3gCfu9" label= "Aufbau Principle"] electrons occupy the lowest energy subshells first
• The 4s overlaps with the 3d subshell so the 4s is filled first
• Remember that you can abbreviate the first five subshells, 1s-3p, as [Ar] representing the configuration of argon (known as the argon core)

Table showing the electronic configuration of the first d-series transition elements

• From your previous studies in chemistry, you should recall there are two exceptions to the Aufbau Principle in the first row of d-block, chromium and copper
• In both cases an electron is promoted from the 4s to the 3d to achieve a half full and full d-subshell, respectively
• Chromium and copper have the following electron configurations, which are different to what you may expect:
  • Cr is [Ar] 3d⁵ 4s¹ not [Ar] 3d⁴ 4s²
  • Cu is [Ar] 3d¹⁰ 4s¹ not [Ar] 3d⁹ 4s²
• This is because the [Ar] 3d⁵ 4s¹ and [Ar] 3d¹⁰ 4s¹ configurations are energetically more stable and are preferred configurations
• When forming cations, remove the 4s electrons first

Answer

Step 1: Write out the electron configuration of the atom first:

Mn atomic number = 25

1s²2s²2p⁶3s²3p⁶4s²3d⁵

2 + 2 + 6 + 2 + 6 + 2 + 5 = 25 electrons

Step 2: Subtract the appropriate number of electrons starting from the 4s subshell

Mn(III) = 22 electrons

1s²2s²2p⁶3s²3p⁶3d⁴

Forming Complex Ions

• Another property of transition elements caused by their ability to form variable oxidation states, is their ability to form complex ions
• A complex ion is a molecule or ion, consisting of a central metal atom or ion, with a number of molecules or ions surrounding it
• A molecule or ion surrounding the central metal atom or ion is called a ligand
• Due to the different oxidation states of the central metal ions, a different number and wide variety of ligands can form bonds with the transition element
  • For example, the chromium(III) ion can form [Cr(NH₃)₆]³⁺, [Cr(OH)₆]^3- and [Cr(H₂O)₆]³⁺ complex ions