Question

\(\Lambda\) transition element \(\mathrm{X}\) has the configuration \([\Lambda \mathrm{r}] 3 \mathrm{~d}^{5}\) in its \(+3\) oxidation state. Its atomic number is (1) 22 (2) 25 (3) 26 (4) 19

Short answer

The atomic number is 25.

Step-by-step solution

Understand the Given Configuration

Note that the element \( \text{X} \) is in its \( +3 \) oxidation state, and its electronic configuration is \[ [\Lambda\text{r}] 3d^5 \]. This means we need to find an element where the \( 3+ \)-state configuration corresponds to \( [\Lambda\text{r}] 3d^5 \).

Recall Electronic Configuration of the Neutral Atom

Determine the electronic configuration of the neutral atom. Adding 3 electrons to \( 3d^5 \) gives \[ [\Lambda\text{r}] 3d^5 4s^2 \]. This implies the neutral atom has two additional electrons in the 4s orbital.

Identify the Position in the Periodic Table

Transition elements from \text{Sc} \( 21 \) to \text{Zn} \( 30 \). With \( 3d^5 4s^2 \), the neutral atom in question has 25 electrons (20 from \( [\Lambda\text{r}] \) and 5 in \( 3d \) and \( 4s \) orbitals).

Conclude the Atomic Number

From the above configuration, deduce that the neutral element is Manganese (Mn), which has an atomic number of 25.

Key concepts

Electronic Configuration

The electronic configuration refers to the distribution of electrons in an atom's orbitals. It's a way to understand how electrons occupy different energy levels and sublevels around an atom's nucleus. In the exercise, we saw the configuration \([\Lambda\text{r}] 3d^5\) for element X in its \(+3\) oxidation state. This notation tells us about the arrangement of electrons after losing some during ionization. For a neutral atom before ionization, adding three electrons results in \([\Lambda\text{r}] 3d^5 4s^2\). This is important as it helps identify the position of an element in the periodic table and predict its chemical behavior. \
When learning about electronic configurations: \

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• Remember that electrons fill orbitals in a specific sequence governed by the Aufbau principle, Hund's rule, and Pauli exclusion principle. \
• Use notations like \([\text{Ar}] 3d^5 4s^2\) to compactly represent the electron arrangements of elements beyond the first few in the periodic table. \

The exercise's configuration helped us understand the neutral atomic electron arrangement and identify the element as Manganese (Mn), atomic number 25.

Oxidation States

Oxidation states indicate the degree of oxidation (loss of electrons) of an atom in a chemical compound. It shows how many electrons an atom has gained or lost compared to its neutral state. The given exercise specifies the oxidation state as \(+3\). This means element X has lost three electrons.
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Key points for understanding oxidation states:
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• Positive oxidation states indicate loss of electrons. Negative states imply gain of electrons. \
• Transition elements typically exhibit multiple oxidation states due to the closeness in energy of their 4s and 3d electrons. \

In the provided example, X in its +3 oxidation state had the configuration \([\text{Ar}] 3d^5\). By adding the three lost electrons back (\([\text{Ar}] 3d^5 4s^2\)), we got the neutral atom's configuration. This led us to conclude the atomic number and identify X as Manganese (Mn). Oxidation states are crucial in understanding the bonding, structures, and reactivity of transition elements.

Periodic Table

The periodic table arranges elements based on their atomic numbers and similar properties. It's a roadmap for understanding elements' behaviors, trends, and relationships. Transition elements, specifically, are those in the d-block, known for their variable oxidation states and formation of colorful compounds.
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In the exercise, we dealt with a transition element. Key trends in this context include:

• Transition elements are found in groups 3-12. \
• They often have incomplete d subshells, allowing for multiple oxidation states and varied chemistry. \

By using the periodic table, we identified Manganese (Mn) as having 25 electrons. Its placement among transition metals guided our understanding of its electron configuration \([\text{Ar}] 3d^5 4s^2\) and its typical oxidation states. The periodic table is a vital tool in predicting and explaining the chemical behavior of elements. Understanding its layout and trends helps students solve problems related to electronic configurations and oxidation states efficiently.