Problem 147 - A Complete Resource Book in Chemistry for JEE Main

Question

Atomic No. of \(\mathrm{Fe}=26\); Number of electrons present in 3 d orbital in \(\mathrm{Fe}^{2+}\) ion is

Step-by-Step Solution

Answer

The \(\mathrm{Fe^{2+}}\) ion has 6 electrons in the 3d orbital.

Step 1: Determine Electron Configuration of Neutral Iron

The atomic number of iron is 26, which means a neutral iron atom has 26 electrons. The electron configuration for iron is: \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^6 \] Here, the electrons fill the orbitals in order of increasing energy levels.

Step 2: Account for the Iron Ion Charge

An \(\mathrm{Fe}^{2+}\) ion has lost 2 electrons compared to a neutral iron atom. Typically, these electrons are removed from the outermost shell first, which in this case is the 4s orbital.

Step 3: Adjust Electron Configuration for \(\mathrm{Fe^{2+}}\)

To account for the 2 electrons lost in \(\mathrm{Fe^{2+}}\), remove them from the 4s orbital: \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^6 \] Notice the 4s electrons are removed, so the electrons present are from the 3d orbital downwards.

Step 4: Count Electrons in the 3d Orbital

After removing the electrons from the 4s orbital, 6 electrons remain in the 3d orbital for \(\mathrm{Fe^{2+}}\). Thus, there are 6 electrons in the 3d orbital.

Key Concepts

Iron

Iron is a well-known metallic element represented by the symbol Fe on the periodic table. It is one of the most abundant elements on Earth and has been widely used throughout human history for its strength and versatility. Iron can be found in various minerals and it's an essential component in both industrial applications and biological systems. For instance, iron plays a crucial role in the formation of hemoglobin, which is necessary for transporting oxygen in the blood.

Iron belongs to the transition metals, found in the central block of the periodic table. Its physical properties, such as high melting and boiling points, derive from its strong metallic bonding. Chemically, iron often forms compounds by losing electrons from its outer shell, achieving a stable electronic configuration similar to that of noble gases.

Fe2+ Ion

An \( ext{Fe}^{2+}\) ion, also known as ferrous ion, is formed when a neutral iron atom loses two electrons. This process is termed oxidation, and the resulting ion has a charge of +2. In redox reactions, which commonly occur in electrochemistry and biochemistry, the ferrous ion often acts as the reducing agent.

The loss of electrons results in changes in the properties of iron, such as its color and reactivity. Iron ions can combine with different anions to form various types of ionic compounds such as iron sulfate, iron chloride, etc., each with distinct chemical properties and uses.

3d Orbital

Orbitals are regions around an atom's nucleus where electrons are likely to be found. Each orbital can hold a maximum of two electrons. The 3d orbital is one of the five d orbitals found from the third energy level onward in an atom's electron configuration.

These d orbitals have a more complex shape compared to the s and p orbitals, and they play a significant role in an element's magnetic properties and its ability to form various coordination complexes. In the case of iron, the 3d orbital is partially filled, which is typical for transition metals. Specifically for \( ext{Fe}^{2+}\), the 3d orbital holds six electrons, contributing to the metallic and chemical properties of iron.

Atomic Number

The atomic number of an element is a fundamental property that corresponds to the number of protons found in the nucleus of an atom of that element. For iron, the atomic number is 26, which means each iron atom has 26 protons. This number is not only critical for identifying the element but also determines its position on the periodic table.

Moreover, the atomic number gives insight into the electron configuration of the element. In a neutral atom, the number of electrons equals the atomic number, yielding a balanced electric charge. Understanding the atomic number is vital for determining how an atom will bond chemically and what types of ions or isotopes it can form. For example, when the iron atom loses two electrons, becoming \( ext{Fe}^{2+}\), it is the atomic number that helps predict the resulting electronic structure.