Problem 15 - Chemistry: Introducing Inorganic, Organic and Physical Chemistry

Question

Give examples of neutral homonuclear and heteronuclear diatomic molecules that are isoelectronic with \(\mathrm{C}_{2}^{2-}\). (Section 4.11 ).

Step-by-Step Solution

Answer

\(\mathrm{N}_2\) and \(\mathrm{CO}\) are isoelectronic with \(\mathrm{C}_{2}^{2-}\).

Step 1: Understanding Isoelectronic Species

Isoelectronic species are atoms, ions, or molecules that have the same number of total electrons. To find species that are isoelectronic with \(\mathrm{C}_{2}^{2-}\), we first need to determine the electron count of \(\mathrm{C}_{2}^{2-}\).

Step 2: Calculate the Total Electrons for \(\mathrm{C}_{2}^{2-}\)

Carbon (\(\mathrm{C}\)) has 6 electrons. A \(\mathrm{C}_2\) molecule would have \(6 + 6 = 12\) electrons. The 2- ion implies an addition of two more electrons, resulting in a total of 14 electrons for \(\mathrm{C}_{2}^{2-}\).

Step 3: Identify Neutral Diatomic Molecules with 14 Electrons

Neutral diatomic molecules have a shared electron count based on the atomic number of the elements involved. For homonuclear molecules, \(\mathrm{N}_2\) has \(7 + 7 = 14\) electrons, making it isoelectronic with \(\mathrm{C}_{2}^{2-}\). For heteronuclear molecules, \(\mathrm{CO}\), with carbon (6 electrons) and oxygen (8 electrons), totals 14 electrons and is also isoelectronic with \(\mathrm{C}_{2}^{2-}\).

Key Concepts

Diatomic Molecules

Diatomic molecules are composed of only two atoms and are a basic form of chemical compounds. These atoms can either be of the same element or different elements, forming either homonuclear or heteronuclear diatomic molecules respectively. A key characteristic of diatomic molecules is their simplicity in structure, which makes them an excellent basis for studying chemical bonding and molecular interactions.
Common examples include familiar molecules like oxygen ( O_2 ) and hydrogen ( H_2 ). In the context of isoelectronic species, diatomic molecules provide a straightforward comparison for electron counts and bonding scenarios. When comparing diatomic molecules to identify isoelectronic species, ensure that the total number of electrons matches as it does in the species being compared, such as C_2^{2-} .

Electron Count

The electron count in a species determines its electron configuration and impacts its chemical properties. For the purpose of identifying isoelectronic species, understanding how to count electrons accurately is crucial.
To find the electron count of C_2^{2-} , you start by recognizing that each carbon atom has 6 electrons. In its molecular form C_2 , this results in a total of 12 electrons initially. Because it carries a 2- charge, two additional electrons must be added, bringing the total to 14 electrons. Thus, any species seeking to be isoelectronic with C_2^{2-} must also possess exactly 14 electrons.

• Carbon has 6 electrons per atom.
• C_2 molecule totals 12 electrons.
• Addition of 2 electrons due to 2- charge brings the total to 14 electrons.

Homonuclear Molecules

Homonuclear molecules are diatomic molecules made up of two atoms of the same element. A classic example of a homonuclear molecule is nitrogen ( N_2 ), which plays an important role in this exercise due to its electron count. In a homonuclear diatomic molecule like N_2 , each nitrogen atom contributes 7 electrons, making a total of 14 electrons when combined. This electron count makes N_2 isoelectronic with C_2^{2-} .
Understanding homonuclear molecules helps simplify the process of finding isoelectronic species, as it narrows the focus to molecules with symmetrical electronic distribution and identical atomic numbers. This symmetry allows for easier predictions about bonding and molecular behavior.

Heteronuclear Molecules

Heteronuclear molecules consist of two different atoms and are another avenue through which one can identify isoelectronic species. Unlike homonuclear molecules, heteronuclear molecules bring together atoms of different elements.
This combination can present varied bonding interactions and thus, different properties altogether. A well-known isoelectronic heteronuclear molecule to C_2^{2-} is carbon monoxide ( CO ). Here, carbon provides 6 electrons, while oxygen contributes 8 electrons, collectively summing to 14 electrons.

• Carbon provides 6 electrons.
• Oxygen supplies 8 electrons.
• Combined electron count equals 14, matching C_2^{2-} .

Different atomic compositions in heteronuclear molecules afford them unique qualities. Approaching isoelectronic tasks with this diversity provides enriching insight into how various elements interact.