Question

The highest oxidation state for the early transition metals Sc, Ti, \(\mathrm{V}, \mathrm{Cr}\), and \(\mathrm{Mn}\) is the periodic group number. The highest oxidation state for the later transition elements \(\mathrm{Fe}\), Co, and \(\mathrm{Ni}\) is less than the periodic group number. Explain.

Short answer

Early transition metals reach oxidation states equal to group number; later ones can't, due to increased electron removal energy.

Step-by-step solution

Identify Transition Metals and Groups

Identify the group numbers for each transition metal. Scandium (Sc) is in group 3, Titanium (Ti) is in group 4, Vanadium (V) is in group 5, Chromium (Cr) is in group 6, and Manganese (Mn) is in group 7. Iron (Fe), Cobalt (Co), and Nickel (Ni) belong to group 8, 9, and 10, respectively.

Understand Highest Oxidation States

Early transition metals (up to Mn) can show an oxidation state equal to their group number due to the availability of unpaired d electrons. These metals can lose all their d electrons plus their s electrons for bonding.

Limitations for Later Transition Metals

For later transition metals (Fe, Co, Ni), the highest oxidation states are usually less than the group number because the energy required to remove d electrons increases as the d orbitals become more filled. Additionally, the increasing nuclear charge pulls electrons closer to the nucleus, making them harder to remove.

Conclusions on Periodic Trends

The trend in the oxidation states is due to the balance between the effective nuclear charge and the energy needed to remove electrons. As we move from early to later transition metals, the ability to achieve high oxidation states decreases because the removal of electrons becomes energetically unfavorable.

Key concepts

Oxidation States

The concept of oxidation states is essential in understanding how transition metals form compounds. Oxidation states indicate the number of electrons an atom can lose, gain, or share when bonding.
Transition metals, such as Scandium (Sc) to Manganese (Mn), can reach oxidation states up to their group number on the periodic table. This flexibility is due to their available unpaired d and s electrons, which can be used in bonding.
For later transition metals like Iron (Fe), Cobalt (Co), and Nickel (Ni), their oxidation states are typically lower than their group numbers. This is because as d orbitals fill with electrons, it becomes more difficult to remove them. The energy required to ionize these electrons increases, limiting their oxidation potential.

Periodic Table Trends

Transition metals display a fascinating trend in their ability to reach certain oxidation states across the periodic table. The difference between early and late transition metals can be traced back to their placement within the d-block.
Early transition metals, positioned at the beginning of the d-block, have fewer d electrons. This allows them to achieve oxidation states equal to their group numbers, as their unpaired electrons can easily participate in bonding.
In contrast, later transition metals have more filled d orbitals. The electrons are held more tightly due to increased nuclear charge, resulting in lower maximum oxidation states. Hence, as you move from left to right across the period, the achievable oxidation states generally decrease.

Electron Configuration

Electron configuration helps explain why transition metals behave differently when forming oxidation states. The distribution of electrons within an atom's orbitals can determine how easily it forms bonds.
Early transition metals, with fewer d electrons, show versatility in achieving higher oxidation states because they can shed more electrons. Their electron configurations allow them to use both s and d electrons for bonding.
However, later transition metals, with nearly full d orbitals, have less flexibility. Their electrons are more tightly bound due to higher nuclear charge, and thus, their oxidation numbers are constrained. Understanding these configurations is key in predicting how an element might behave in chemical reactions.

Early and Late Transition Metals

Transition metals can be broadly categorized into early and late, each showing distinct chemical properties. Early transition metals are those from groups 3 to 7, like Scandium (Sc) through Manganese (Mn).
They typically exhibit higher oxidation states corresponding with their group numbers. This is because they have available d electrons that aren't tightly bound, allowing them to engage in more active bonding.
On the other hand, late transition metals like Iron (Fe), Cobalt (Co), and Nickel (Ni) show lower oxidation states. Filled d orbitals make it less energetically favorable to remove electrons, leading to lower oxidation potentials. This distinction is vital for predicting the behavior of these metals in various chemical processes.