Edexcel A Level Chemistry:复习笔记6.2.1 Transition Metals

General Properties of Transition Metals

 

  • Transition metals are elements with an incomplete d-subshell that can form at least one stable ion 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

6.2.1-Transition-elements-and-d-block-elements

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 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

6.2-Chemistry-of-Transition-Elements-Electronic-configuration-of-transition-elements-table

  • From AS Chemistry you should recall two exceptions to the Aufbau Principle, 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

Worked Example

Writing electronic configuration of transition element ions

State the full electronic configuration of the manganese(III) ion

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

General properties

  • Although the transition elements are metals, they have some properties unlike those of other metals on the periodic table, such as:
    • Variable oxidation states
    • Form complex ions
    • Form coloured compounds
    • Behave as catalysts

Variable Oxidation Number

  • Like other metals on the periodic table, the transition elements will lose electrons to form positively charged ions
  • However, unlike other metals, transition elements can form more than one positive ion
    • They are said to have variable oxidation states
  • Because of this, Roman numerals are used to indicate the oxidation state on the metal ion
    • For example, the metal sodium (Na) will only form Na+ ions (no Roman numerals are needed, as the ion formed by Na will always have an oxidation state of +1)
    • The transition metal iron (Fe) can form Fe2+ (Fe(II)) and Fe3+ (Fe(III)) ions
  • When transition elements forms ions they lose electrons from the 4s subshell first
  • This is because when the orbitals are occupied, the repulsion between electrons pushes the 4s into a higher energy state so that it now becomes slightly higher in energy than the 3d subshell
    • The 4s is now the outer shell and loses electrons first
  • The loss of the 4s electrons means that +2 is a common oxidation state in transition metals
  • The reason why the transition metals have variable oxidation states all comes down to energy

Table showing the Common Oxidation States of Transition Elements

6.2.5-Oxidation-states-of-transition-elements-table

 

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