Question

Xenon dioxide is a slightly stable molecule that contains a noble gas. Write the electron dot formula and draw the structural formula for \(\mathrm{XeO}_{2}\).

Short answer

XeO₂ has 20 valence electrons, a bent shape, each Xe-O bond double, and meets the octet rule for oxygen.

Step-by-step solution

Determine Total Valence Electrons

Xenon (Xe) is in Group 18 of the periodic table and has 8 valence electrons. Each oxygen (O) in Group 16 has 6 valence electrons. Therefore, for \( \mathrm{XeO}_2 \), you sum the electrons as: \( 8 + 2 \times 6 = 20 \) valence electrons.

Predict Molecular Shape

Xenon dioxide is expected to be bent, similar to water (\( \mathrm{H}_2\mathrm{O} \)). Xenon will be the central atom with two oxygen atoms arranged around it. Each oxygen will be double-bonded to xenon.

Distribute Electrons in Lewis Structure

First, place the central xenon atom and connect it to two oxygens using double bonds. This uses \(2\times2\times2 = 8\) electrons. Place the remaining 12 electrons around the oxygens to fill their octets, as xenon can accommodate more than 8 electrons.

Confirm Octet Rule and Electron Count

After drawing the double bonds and placing lone pairs, verify each oxygen has 8 electrons around it (including the bonded electrons), completing their octets, and xenon should have 12 electrons in total. Check you have exactly 20 electrons total.

Draw the Structural Formula

Use your Lewis structure to draw the structural formula, indicating double bonds between xenon and each oxygen. The bond angle will be slightly less than 120 degrees due to the bent shape of the molecule.

Key concepts

Valence Electrons

Valence electrons play a crucial role in chemical bonding and Lewis structures. These electrons are the outermost electrons of an atom and are directly involved in the formation of chemical bonds.
By sharing, gaining, or losing valence electrons, atoms can achieve more stable configurations, closely resembling those of noble gases.
Here’s how valence electrons are determined:

• For main group elements, the group number in the periodic table helps predict the number of valence electrons. For example, elements in Group 18 have 8 valence electrons.
• Xenon (Xe), being a noble gas, already has a full valence shell of 8 electrons, but it can participate in bonding in certain situations like in the formation of xenon dioxide (XeO$_2$).
• Oxygen (O) in Group 16 has 6 valence electrons, needing only 2 more electrons for stability (i.e., fulfilling the octet rule).

Understanding the concept of valence electrons is crucial for drawing Lewis structures, as it determines how atoms will interact with one another to form molecules.

Octet Rule

The octet rule is a guiding principle in bonding, especially for main group elements. This rule states that atoms are generally most stable when they have eight electrons in their valence shell, mimicking the electron configuration of noble gases.
While this rule works well for many elements, it has its exceptions and limitations:

• For lighter elements, like hydrogen which achieves stability with two electrons (similar to helium), the rule is adapted accordingly.
• Some elements like xenon (a noble gas) can exceed the octet rule due to available d-orbitals, allowing them to have more than eight electrons in certain compounds like XeO$_2$.
• When drawing Lewis structures, fulfilling the octet for each atom is a key step, but awareness of possible exceptions is important.

When working with Lewis structures, always check that the octet rule is satisfied for elements where it applies, while being mindful of elements known to expand their octets.

Noble Gases

Noble gases are a unique group of elements found in Group 18 of the periodic table. These elements—such as helium, neon, and xenon—are characterized by having a full set of valence electrons, typically leading to a lack of chemical reactivity.
Here's why they are special:

• Their full valence shells mean noble gases naturally exhibit a stable electron configuration, making them largely inert.
• Despite their stability, some noble gases like xenon can form compounds under certain conditions due to their size and ability to expand the valence shell.
• Noble gases serve as a benchmark for other elements, which tend to form bonds in an effort to achieve a similar stable electron arrangement.

Understanding noble gases helps us appreciate why elements like xenon can participate in bonding (like in xenon dioxide) although they are often thought of as non-reactive. This insight is essential when tackling problems involving unusual compounds of noble gases.