Question

Which of the following configurations represents a noble gas? (a) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{10} 4 s^{2} 4 p^{6} 4 d^{10} 5 s^{2}\) (b) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{10} 4 s^{2} 4 f^{14} 5 s^{2}\) (c) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{10} 4 s^{2} 4 p^{6} 4 d^{10} 5 s^{2} 5 p^{6}\) (d) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{10} 4 s^{2} 4 p^{6} 4 d^{10} 5 s^{2} 5 p^{3}\)

Short answer

Configuration (c) represents a noble gas.

Step-by-step solution

Recall the Definition of Noble Gases

Noble gases are elements with a completely filled outermost electron shell. This means that all the s and p orbitals in their highest energy level are fully occupied. Usually, for noble gases, this results in an electron configuration that ends in either \(s^2 p^6\) or just \(s^2\) for Helium.

Analyze Option (a)

The electron configuration ends with \(4p^6\). However, there is an additional \(5s^2\) indicating that the shell is not fully occupied at its highest energy level, which means it is not a noble gas.

Analyze Option (b)

The electron configuration ends with \(4f^{14} 5s^2\). With the incomplete \(5s\) orbital and no \(5p\) electrons, this is not a noble gas configuration.

Analyze Option (c)

The electron configuration ends with \(5p^6\). Since the s and p orbitals of the highest energy level (n=5) are fully occupied, this represents a noble gas configuration.

Analyze Option (d)

The electron configuration ends with \(5p^3\). With the \(5p\) orbital not fully occupied, this is not the configuration of a noble gas.

Key concepts

Electron Configuration

Understanding the electron configuration of an atom is like reading a map of where its electrons are located. Electrons are found in regions around the nucleus called orbitals, and these orbitals are organized into energy levels and sublevels. The electron configuration provides a layout that shows how the orbitals are filled according to the 'building-up' (Aufbau) principle.

This principle states that electrons fill orbitals starting from the lowest energy level to the higher ones. Each orbital can hold a specific number of electrons, for example, s orbitals can hold 2 electrons and p orbitals can hold 6. The configuration is read by following the sequence of filled energy levels and sublevels, kind of like how you would read sentences in a book.

• The '1s' orbital is filled first (holding up to 2 electrons).
• Then the '2s' followed by '2p' (with the 'p' holding up to 6 electrons), and so on.

When all the orbitals in an energy level are fully filled with electrons, the atom achieves a very stable configuration.

Noble Gases

Noble gases, the VIPs of the periodic table, are known for their 'reserved' chemical nature. They are the elements found in group 18 and have a particularly stable set of electrons, which makes them mostly nonreactive. This stability comes from their electron configurations, which have completely filled s and p orbitals in their outermost energy level.

Helium, the lightweight of the bunch, stays stable just by filling its 1s orbital with two electrons. The others, like Neon, Argon, or Xenon, follow the pattern of having their outermost s and p orbitals fully packed with electrons, specifically an 's^2 p^6' ending. It's like having a full set of luggage when traveling—everything's neatly in place for a hassle-free journey.

Outermost Electron Shell

The outermost electron shell, or valence shell, holds the key to an atom's chemical personality. This shell has the highest energy electrons and determines how the atom will interact or bond with others.

Take noble gases—because their valence shell is fully stocked with electrons, they have no room for more, and therefore, they don't tend to participate in chemical reactions. Imagine the noble gases as people who are completely satisfied with their group of friends and aren't looking to make new connections. For other elements, an incomplete valence shell is like an open invitation to form bonds and react, striving to reach the stability of a noble gas by gaining, losing, or sharing electrons.

Atomic Structure

Diving into the atomic structure, we encounter a tiny but massively influential universe. At the center of this universe is the nucleus, which contains protons and neutrons—this is the control center, deciding the identity of the atom.

Whizzing around the nucleus are the electrons, found in orbitals as mentioned earlier. These electrons are layered like onions in different energy levels, with each level capable of holding a certain maximum number of electrons. The atomic structure is crucial because it determines the element's properties, from its reactivity to the nature of the bonds it forms and even its state of matter under different conditions.