Problem 103 - Chemistry: An Atoms-Focused Approach

Question

Which monatomic ion has a charge of \(1-\) and the condensed electron configuration \([\mathrm{Ne}] 3 s^{2} 3 p^{6} ?\) How many unpaired electrons are there in the ground state of this ion?

Step-by-Step Solution

Answer

Answer: The monatomic ion is Cl\(^{-}\), and it has 0 unpaired electrons in its ground-state electron configuration.

Step 1: Write down the given electron configuration

We are given the condensed electron configuration as \([\mathrm{Ne}] 3 s^{2} 3 p^{6}\).

Step 2: Expand the electron configuration

To identify the element, we need to expand the condensed electron configuration. The electron configuration of Ne (neon) is \(1 s^2 2 s^2 2 p^6\). So, the expanded electron configuration will be \(1 s^2 2 s^2 2 p^6 3 s^{2} 3 p^{6}\).

Step 3: Identify the element

To find the element, we need to count the number of electrons present in the above-expanded electron configuration. Summing the electrons in all the orbitals, we get: \(2 + 2 + 6 + 2 + 6 = 18\). Since the ion has a charge of \(1-\), this means that the neutral atom would have had 17 electrons. This corresponds to Chlorine (Cl), which has an atomic number of 17. Therefore, the monatomic ion we are looking for is the Chloride ion (Cl\(^{-}\)).

Step 4: Determine the number of unpaired electrons

In the ground-state electron configuration, there are no unpaired electrons present in the orbital configuration of Cl\(^{-}\) ion. All the electrons are paired in their respective orbitals: \(1 s^2 2 s^2 2 p^6 3 s^{2} 3 p^{6}\). The presence of a completely filled p-orbital indicates that there are no unpaired electrons. So, the correct answer is that the monatomic ion is Cl\(^{-}\), and it has 0 unpaired electrons in its ground-state electron configuration.

Key Concepts

Electron Configuration

Electron configuration is a way to describe the arrangement of electrons in an atom. It shows us precisely how electrons fill into various energy levels and orbitals.
To visualize electron configuration, think of it as an address for each electron. The complete address tells you exactly where the electron 'lives' in the atom.

• The first part states the energy level, noted by numbers (like 1, 2, 3, etc.).
• The next part is the type of orbital, noted by letters (s, p, d, and f).
• Finally, the superscript numbers indicate the number of electrons in each orbital.

For instance, in the given exercise, the electron configuration of Cl^- ion is \([\text{Ne}] \ 3s^2 \ 3p^6\). This shows that the outermost energy level 3 has a total of eight electrons in its s and p orbitals, imitating the stable configuration of noble gases.

Unpaired Electrons

Unpaired electrons are those electrons that do not have a partner in their orbital. In the field of chemistry, unpaired electrons can greatly influence the properties of an atom.

When electrons occupy orbitals, they usually "pair up" to fill them. Each orbital can hold a maximum of two electrons, spinning in opposite directions. This pairing leads to magnetic properties:

• Atoms with unpaired electrons tend to be paramagnetic, which means they are attracted to magnetic fields.
• Atoms without unpaired electrons are diamagnetic, so they are slightly repelled by magnetic fields.

For the Cl^- ion in the original exercise, all electrons are paired \(1s^2 \ 2s^2 \ 2p^6 \ 3s^2 \ 3p^6\), meaning it is diamagnetic with no unpaired electrons in its ground state.

Chloride Ion

A chloride ion is a common monatomic ion represented as Cl^-. It is formed when a chlorine atom gains an extra electron to achieve a stable electron configuration similar to that of a noble gas, like Argon.

Here are a few important characteristics:

• It has a total of 18 electrons, which is one more than a neutral chlorine atom.
• The negative charge indicates that the ion has one more electron than protons, making it a negatively charged particle.

In chemical reactions, chloride ions often participate by pairing with positively charged ions to form compounds. For example, sodium chloride (NaCl) is a very well-known compound formed when sodium ions pair with chloride ions. The added electron fills the 3p orbital, completing the outer shell and providing stability.