Problem 96 - Chemistry: The Central Science

Question

Use orbital diagrams to illustrate what happens when an oxygen atom gains two electrons. Why is it extremely difficult to add a third electron to the atom?

Step-by-Step Solution

Answer

When an oxygen atom gains two electrons, it becomes an oxide ion (O²⁻) with the electron configuration 1s², 2s², 2p⁶. The process can be illustrated using the orbital diagram: O²⁻: 1s: ↑↓ 2s: ↑↓ 2p: ↑↓ ↑↓ ↑↓ It is extremely difficult to add a third electron due to increased electrostatic repulsion, high energy requirement to occupy the next higher energy level (3s), and the stability of the O²⁻ ion with a full 2p subshell. Adding a third electron would disturb this stable configuration and create an unstable state, making it unfavorable to accept the third electron.

Step 1: Draw the orbital diagram for an oxygen atom

In order to draw the orbital diagram for an oxygen atom, we need to understand its electron configuration. Oxygen has an atomic number of 8, which means it has 8 electrons. Its electron configuration is 1s², 2s², 2p⁴. Now we can draw the orbital diagram: 1s: ↑↓ 2s: ↑↓ 2p: ↑ ↑ ↑

Step 2: Illustrate the process of gaining two electrons

When an oxygen atom gains two electrons, it becomes an oxide ion (O²⁻). The electrons will fill the available lowest-energy orbitals. As we can see from the oxygen atom orbital diagram, two more electrons can be added to the 2p orbitals: O²⁻: 1s: ↑↓ 2s: ↑↓ 2p: ↑↓ ↑↓ ↑↓

Step 3: Explain why it is difficult to add a third electron

Adding a third electron to the oxide ion (O²⁻) is extremely difficult due to several reasons: 1. Electrostatic repulsion: The negatively charged electrons repel each other. Adding a third electron would increase the electron-electron repulsion within the ion, making it very difficult for the third electron to be added. 2. Energy requirement: The addition of a third electron would require it to occupy the next higher energy level, which is 3s. This would require a significant amount of energy to overcome the ionization energy, making it very difficult to add the third electron. 3. Stability: The O²⁻ ion has a stable electron configuration with a full 2p subshell. Adding a third electron would disturb this stable configuration and create an unstable state, making it unfavorable for the ion to accept the third electron.

Key Concepts

Electron Configuration

Electron configuration is a system used to describe the arrangement of electrons in atoms and ions. For an oxygen atom, which has an atomic number of 8, the electrons are arranged according to energy levels. These configurations are described using the notation of subshells like 1s, 2s, and 2p.

Oxygen’s electron configuration is depicted as 1s², 2s², 2p⁴. The superscripts indicate the number of electrons in each subshell. Knowing this configuration allows us to visualize the electronic arrangement using an orbital diagram, where each orbital is represented by boxes or lines, and the electrons are shown as arrows indicating their spin.

Understanding electron configuration is key because it helps predict how atoms will interact in chemical reactions and form bonds.

Oxygen Atom

The oxygen atom is a crucial element in chemistry, represented by the symbol 'O' and an atomic number of 8. This number tells us that an oxygen atom contains 8 protons and, in a neutral state, 8 electrons.

Being a non-metal, oxygen is highly electronegative, which means it has a strong tendency to attract electrons towards itself. This property is essential in its ability to form oxides, such as O²⁻, where oxygen gains two additional electrons.

In its neutral state, oxygen has 2 electrons in its outer 2p orbital, seeking to achieve a stable electronic configuration similar to noble gases by gaining electrons.

Electron Repulsion

Electron repulsion is a fundamental concept in explaining why electrons distribute themselves across different orbitals in an atom. Electrons carry negative charges and naturally repel each other, preferring to occupy the most spacious and energy-efficient position possible.

When an oxygen atom is neutral, the repulsion between electrons determines their arrangement in the orbitals. As electrons are added to an atom or ion, the repulsion increases. This is crucial in understanding why adding electrons beyond a certain point, like for an oxide ion O²⁻, becomes extremely challenging.

• This increased repulsion makes it difficult to add a third electron as it would require significant energy to overcome the repulsive forces within a compact orbital space.

Stability of Ions

The stability of ions heavily depends on their electron configurations. An ion becomes more stable when it achieves a noble gas configuration. For the oxygen atom, acquiring two additional electrons results in the O²⁻ ion with a full 2p subshell, mirroring the noble gas neon.

This configuration is energetically favorable, meaning it is more difficult and less likely to add another electron to O²⁻ without distorting this stable state. The energy required to force an additional electron into a new higher energy level is immense.

Thus, maintaining a complete outer electron shell ensures the stability of ions and plays a critical role in predicting and understanding the reactive nature of different elements.