Problem 53 - Chemistry Matter and Change

Question

The transition elements have their valence electrons in orbitals of more than one energy level, but the representative elements have their valence electrons in orbitals of only one energy level. Show this by using the electron configurations of a transition element and a representative element as examples.

Step-by-Step Solution

Answer

The electron configurations of Iron (Fe), a transition element, and Oxygen (O), a representative element, are as follows: Iron (Fe): \[ 1s^2 \; 2s^2 \; 2p^6 \; 3s^2 \; 3p^6 \; 4s^2 \; 3d^6 \] Oxygen (O): \[ 1s^2 \; 2s^2 \; 2p^4 \] Iron's valence electrons are in both 4s² and 3d⁶ orbitals, which have different energy levels, while Oxygen's valence electrons are only in the 2p⁴ orbital, having only one energy level. This demonstrates the given statement about transition and representative elements' valence electrons.

Step 1: Choose a transition element and a representative element

We will choose a transition element and a representative element as examples. For the transition element, let's take Iron (Fe) and for the representative element, let's choose Oxygen (O).

Step 2: Write down the electron configurations.

Now, we have to write the electron configurations for both Iron (Fe) and Oxygen (O). Iron (Fe) has an atomic number of 26, so its electron configuration is: \[ 1s^2 \; 2s^2 \; 2p^6 \; 3s^2 \; 3p^6 \; 4s^2 \; 3d^6 \] Oxygen (O) has an atomic number of 8, and its electron configuration is: \[ 1s^2 \; 2s^2 \; 2p^4 \]

Step 3: Identify the valence electrons

Valence electrons are the electrons located in the outermost electron shells of an element. In our case, we need to identify the valence electrons for Iron (Fe) and Oxygen (O). For Iron (Fe): \[ 1s^2 \; 2s^2 \; 2p^6 \; 3s^2 \; 3p^6 \; (\underline{4s^2 \; 3d^6}) \] For Oxygen (O): \[1s^2 \; 2s^2 \; (\underline{2p^4}) \]

Step 4: Compare the valence electron configurations

Based on the electron configurations of Iron (Fe) and Oxygen (O), let's compare their valence electrons. For Iron (Fe), we have 4s² and 3d⁶ as its valence orbitals, thus having valence electrons in orbitals of more than one energy level. For Oxygen (O), we have only the 2p⁴ orbital where the valence electrons reside, which means its valence electrons are in orbitals of just one energy level. This shows that the transition element (Iron) has its valence electrons located in orbitals of more than one energy level, while the representative element (Oxygen) has its valence electrons in orbitals of only one energy level, as required by the exercise.

Key Concepts

Transition Elements

Transition elements, often referred to as transition metals, occupy the d-block of the periodic table. These elements include metals such as iron (Fe), copper (Cu), and nickel (Ni). A defining feature of transition elements is the presence of valence electrons in their d subshells. This results in unique properties like variable oxidation states, the formation of colored compounds, and catalytic behavior. One key characteristic of transition metals is that their valence electrons are located in orbitals across multiple energy levels. For example, iron (Fe) has an electron configuration of \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^6\). Notice the valence electrons are in both the 3d and 4s orbitals.
This placement affects how they bond and interact with other elements. The presence of d electrons allows these elements to bridge gaps in complex chemical processes, making them crucial for industries ranging from manufacturing to medicine.

Valence Electrons

Valence electrons are the electrons found in the outermost shell of an atom. They are pivotal in determining how an atom will react chemically with other elements. In general, these are the electrons involved in forming bonds. For transition elements, such as iron (Fe), the valence electrons include those from the outermost d or s subshells, extending across multiple energy levels. This characteristic leads to complex bonding and multiple oxidation states. On the contrary, representative elements, like oxygen (O), have a simpler arrangement where valence electrons are only in one outer energy level. Oxygen's configuration \(1s^2 \, 2s^2 \, 2p^4\) shows valence electrons in the same energy level, specifically in the 2p orbital.
Understanding valence electrons helps us predict an element's capability to form bonds and react, which is vital for creating new chemical compounds or technologies.

Energy Levels

Energy levels, or electron shells, represent the regions around the atomic nucleus where electrons are likely to be found. These are defined by quantum numbers and can be visualized as concentric spheres in which electrons orbit the nucleus. Each energy level can hold a specific number of electrons. As you move to higher levels, the capacity increases.

• Level 1 can hold up to 2 electrons.
• Level 2 can hold up to 8 electrons.
• Level 3 can potentially accommodate up to 18 electrons.

For transition elements, the filling of d orbitals occurs after the s orbital of the next highest energy level. This is why in examples like iron, we see the 3d orbital filled after the 4s. Such arrangements are unique to transition metals and explain many of their chemical properties. Conversely, representative elements fill their valence shell in a simpler sequence without involving the d subshells, leading to more straightforward chemical behavior.