Question

What is the electronic configuration of \(\mathrm{O}^{2-}\) ion? (a) \(1 s^{2} 2 s^{2} 2 p^{6}\) (b) \(1 s^{2} 2 s^{2} 2 p^{4}\) (c) \(1 s^{2} 2 s^{2} 2 p^{5}\) (d) \(1 s^{2} 2 s^{2} 2 p^{3}\)

Short answer

The electronic configuration of O^{2-} ion is (a) 1s^2 2s^2 2p^6.

Step-by-step solution

Determine Number of Electrons

First, identify the number of electrons in an oxygen atom. Oxygen has an atomic number of 8, meaning it has 8 electrons as a neutral atom. The O^{2-} ion has gained 2 additional electrons, giving it a total of 10 electrons.

Apply the Aufbau Principle

Next, fill the electron orbitals in the order of increasing energy according to the Aufbau principle. The order is 1s, 2s, then 2p orbitals. Since there are 10 electrons to place, the 1s orbital will be filled with 2 electrons, the 2s orbital will also be filled with 2 electrons, and the remaining 6 electrons will fill the 2p orbitals, which can hold up to 6 electrons.

Write Electronic Configuration

The electronic configuration of the O^{2-} ion is then written considering the electrons in each filled orbital. The 1s orbital holds 2 electrons (1s^2), the 2s orbital holds 2 electrons (2s^2), and the 2p orbitals hold 6 electrons (2p^6).

Key concepts

Oxygen Ion

To understand the nature of an Oxygen ion, it's vital to recognize that ions are atoms that have lost or gained electrons to achieve a stable electronic configuration, often resembling the nearest noble gas. In the case of an oxygen ion with a 2- charge, denoted as \(\mathrm{O}^{2-}\), this means that the oxygen atom has gained two additional electrons.

Oxygen, in its neutral state, has 8 electrons. The addition of two electrons to achieve the \(\mathrm{O}^{2-}\) ion increases the electron count to 10. These extra electrons are added to the oxygen atom's outermost shell, resulting in a full valence shell, which is a desirable state for atoms as it contributes to chemical stability. This gives the ion a similar electron configuration to neon, the noble gas with 10 electrons.

Aufbau Principle

The Aufbau Principle, a fundamental concept in chemistry, provides a roadmap for determining the electronic configuration of an atom or ion. According to this principle, as we build up the electronic configuration, electrons will occupy orbitals in order of increasing energy.

The sequence usually begins with the 1s orbital, followed by the 2s, and then the 2p orbitals, provided they are available in the atom. Each orbital has a specific capacity: the 1s orbital can hold up to 2 electrons, and the 2s and 2p orbitals can each hold up to 2 and 6 electrons, respectively. It is worth noting that the p orbital can have three sublevels, designated as \(p_x\), \(p_y\), and \(p_z\), each capable of holding 2 electrons. When using the Aufbau Principle to fill in the electrons for an oxygen ion, we systematically fill these orbitals in the mentioned order to reach the most stable arrangement.

Electron Orbitals

Electron orbitals are regions around an atom's nucleus where electrons are most likely to be found. These orbitals come in various shapes and sizes, such as spherical (s orbitals) and dumbbell-shaped (p orbitals). Each orbital has a set energy level and can occupy one or more sublevels.

The first energy level has only one s orbital (1s), the second level contains one s orbital (2s) and three p orbitals (2p), and so on for higher energy levels. Electrons in an atom will fill the available orbitals starting from the lowest energy level moving upwards. This organization of electrons helps determine an atom's chemical properties and reactivity. For the \(\mathrm{O}^{2-}\) ion, understanding how electrons fill the 1s, 2s, and 2p orbitals is crucial to depict its electronic configuration accurately.

Atomic Number

The Atomic number defines the identity of an element by indicating the number of protons found in the nucleus of an atom. Moreover, for a neutral atom, the atomic number also represents the number of electrons orbiting the nucleus because atoms are electrically neutral with equal numbers of positive protons and negative electrons.

Oxygen’s atomic number is 8, meaning it has 8 protons and, when neutral, also has 8 electrons. However, when we talk about ions, the number of electrons can be different from the atomic number. For instance, in the oxygen ion \(\mathrm{O}^{2-}\), the number of electrons is greater than the atomic number due to the ion’s negative charge which signifies excess electrons. Understanding the atomic number is thus essential when trying to determine the electronic configuration of an element, whether in its neutral state or ionized form.