IB DP Chemistry: HL复习笔记13.1.1 Transition Elements-翰林国际教育

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

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

The transition elements and the d-block elements

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

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

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 4s¹not [Ar] 3d⁹ 4s²
This is because the [Ar] 3d⁵ 4s¹ and [Ar] 3d¹⁰ 4s¹configurations are energetically more stable and are preferred configurations
When forming cations, remove the 4s electrons first

Writing electronic configuration of transition element ionsState 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

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

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

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

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 from or donating electrons to reagents within the reaction
Substances can also be adsorbed onto their surface and activated in the process

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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