IB Chemistry HL

Revision Notes

13.1.1 Transition Elements

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

6.2.1 Transition elements and d-block elements, downloadable AS & A Level Chemistry revision notes

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

Chemistry of Transition Elements - Electronic configuration of transition elements table, downloadable AS & A Level Chemistry revision notes

  • 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 4snot [Ar] 3d9 4s2
  • This is because the [Ar] 3d5 4s1 and [Ar] 3d10 4sconfigurations are energetically more stable and are preferred configurations
  • When forming cations, remove the 4s electrons first

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
    • Have magnetic properties

Variable Oxidation States

  • 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

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

Forming coloured compounds

  • Another characteristic property of transition elements is that their compounds are often coloured
    • For example, the colour of the [Cr(OH)6]3- complex (where oxidation state of Cr is +3) is dark green
    • Whereas the colour of the [Cr(NH3)6]3+ complex (oxidation state of Cr is still +3) is purple

Transition elements as catalysts

  • Since transition elements can have variable oxidation states, they make excellent catalysts
  • During catalysis, the transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction
  • Substances can also be adsorbed onto their surface and activated in the process

Magnetic Properties

  • Materials are classified as diamagnetic, paramagnetic or ferromagnetic according to their behaviour when placed in an external magnetic field
  • Transition metals exhibit these properties depending on their electronic configurations
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