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Electronic configuration refers to the arrangement of electrons in an atom's orbitals. It is primarily governed by the principles of quantum mechanics. For transition metals, electrons fill the 3d orbitals after the 4s orbitals. This means, for example, that in a neutral titanium atom, the electronic configuration would be

• 1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s² or,
• [Ar] 3d² 4s²,

where [Ar] represents the electron configuration of argon. As electrons are removed (or added), this configuration changes, which affects the chemical properties of the element. For ions, electrons are preferentially removed from the outermost shell first, which often means the 4s electrons are lost before the 3d electrons.

The 3d orbitals are a set of five orbitals in the d subshell with a principal quantum number of 3. These orbitals are filled with electrons after the 4s orbital in the atoms of the transition metals.
Each d orbital can hold a maximum of two electrons, so a complete 3d subshell can hold up to ten electrons. The filling of these orbitals influences the geometry and magnetic properties of the atoms.
When transition metal ions are formed, the electrons in the 3d subshell play a significant role. For example, for the transition metal ions mentioned in the exercise:

• Ti²⁺ has an electron configuration of [Ar] 3d², indicating that the two 3d electrons remain after losing the 4s electrons.
• The role of d orbitals becomes even more significant in the bonding and chemical behavior of the elements.

These metal ions exhibit various oxidation states due to the involvement of these d electrons.

Transition metal atoms can lose different numbers of electrons to form positive ions or cations, resulting in different ionization states. The oxidation state or ionization state is the total number of electrons removed.
These states are pivotal in determining the chemical reactivity and coordination properties of the ions. For example, in the transition metal series question, the ions Ti²⁺, V³⁺, Cr⁴⁺, and Mn³⁺ exhibit different positive ionization states depending on how many electrons have been removed.

• The ionization states can complicate the electron configuration since electrons from the 3d orbitals and 4s orbitals can be involved.
• Higher ionization states generally mean more electrons have been removed, typically from the 4s before the 3d orbitals.

By understanding ionization states, students can predict and explain the behavior of transition metals in chemical reactions and distinguish between different ions of the same element based on their electronic configurations.