S3.1.8 Properties of transition elements (Higher Level Only)

Transition Elements: Definition and Key Properties

1. You’re tasked with designing a material that can withstand extreme conditions, catalyze chemical reactions efficiently, and add aesthetic appeal to its surroundings.
2. What kind of elements would you choose?

Transition elements, located at the center of the periodic table, often meet these requirements due to their remarkable and diverse properties.

What Defines a Transition Element?

1. The term "transition element" refers to elements in the d-block of the periodic table.
2. These elements are defined by having an incomplete d-sublevel either in their neutral atom or in at least one of their ions.
3. This distinction sets them apart from other d-block elements, such as zinc, which does not qualify as a transition element because its $d$-sublevel is completely filled in both its neutral and ionic forms.

Electron Configuration and the d-Sublevel

1. Transition elements occupy groups 3–12 of the periodic table.
2. Their electron configurations typically follow the general pattern:
   $$(n-1)d^{1-10}n{s}^{0-2}$$ where $n$ represents the principal quantum number of the outermost shell.

Key Properties of Transition Elements

Transition elements exhibit a range of unique properties stemming from their partially filled $d$-sublevels.

1. Variable Oxidation States

1. One of the defining features of transition elements is their ability to exhibit variable oxidation states.
2. This is due to the relatively small energy difference between the $s$- and $d$-sublevel electrons, allowing both to participate in bonding.

2. Formation of Colored Compounds

1. Transition elements are renowned for the vibrant colors of their compounds.
2. This property arises from the splitting of the $d$-orbitals in the presence of ligands (molecules or ions that coordinate to the metal ion).
3. The energy gap between the split $d$-orbitals corresponds to the wavelength of visible light.
4. When light is absorbed to promote an electron from a lower to a higher $d$-orbital, the compound displays the complementary color.

3. High Melting Points and Catalytic Activity

High Melting Points

1. Transition elements generally have high melting and boiling points, thanks to their strong metallic bonding.
2. The presence of delocalized $d$-electrons enhances these bonds, contributing to their robustness.

Catalytic Activity

1. Transition elements and their compounds are widely used as catalysts.
2. Their ability to adopt multiple oxidation states and form temporary bonds with reactants allows them to lower the activation energy of a reaction.

4. Magnetism

1. Transition elements often exhibit magnetic properties due to the presence of unpaired electrons in their $d$-sublevels.
2. Magnetism arises from the spin of these unpaired electrons, creating a magnetic field.

Types of Magnetism:

• Paramagnetism: Caused by unpaired electrons that create a weak magnetic field. Observed in elements like iron ($Fe$) and nickel ($Ni$).
• Diamagnetism: Occurs when all electrons are paired, resulting in no magnetic attraction (e.g., zinc $Zn$).
• Ferromagnetism: A stronger form of magnetism where unpaired electrons align in a specific pattern, creating a permanent magnetic field (e.g., iron $Fe$).

Reflection and Review