Question

(a) What is the octet rule? (b) How many electrons must a sulfur atom gain to achieve an octet in its valence shell? (c) If an atom has the electron configuration \(1 s^{2} 2 s^{2} 2 p^{3},\) how many electrons must it gain to achieve an octet?

Short answer

(a) The octet rule states that atoms tend to gain, lose, or share electrons to have eight electrons in their valence shell, making them chemically stable. (b) Sulfur has 6 valence electrons and needs to gain 2 more electrons to achieve an octet. (c) The atom with the electron configuration \(1s^2 2s^2 2p^3\) has 5 valence electrons and needs to gain 3 more electrons to achieve an octet.

Step-by-step solution

(a) Define the octet rule

The octet rule states that atoms tend to gain, lose, or share electrons in such a way that each atom has eight electrons in its valence shell, which is the outermost electron shell. This configuration is very chemically stable, making it the preferred state for elements during chemical reactions.

(b) Electrons sulfur must gain

To find out how many electrons sulfur must gain to achieve an octet, we need to determine the number of valence electrons it currently has. Sulfur is in the 16th group of the Periodic Table (oxygen family), which means that it has 6 valence electrons. To achieve an octet, sulfur must gain 2 more electrons as \(8 - 6 = 2\). Therefore, sulfur needs to gain 2 electrons to have an octet in its valence shell.

(c) Electrons needed for given electron configuration

The given electron configuration is \(1s^2 2s^2 2p^3\). First, we need to determine the number of valence electrons in this configuration. The valence electrons are located in the outermost electron shell, which in this case is the second shell with a total of \(2s^2 2p^3\) electrons. There are 2 electrons in the 2s orbital and 3 electrons in the 2p orbital, making a total of 5 valence electrons. To achieve an octet, this atom needs 8 valence electrons. Therefore, the atom must gain 3 more electrons as \(8 - 5 = 3\). So, the atom with the given electron configuration needs to gain 3 electrons to achieve an octet in its valence shell.

Key concepts

Valence Electrons

Valence electrons play a pivotal role in chemical reactions as they are the outermost electrons of an atom, participating in the bonding process. To understand this concept better, let's consider sulfur from our exercise. It belongs to the 16th group of the Periodic Table and has 6 valence electrons. The valence electrons are like the 'hands' of the atom, reaching out to interact with other atoms.

These interactions are often dictated by the atoms' goal to achieve a stable configuration, typically by having eight valence electrons, which is known as the octet rule. For sulfur, gaining 2 more electrons would fulfill this requirement. Understanding the count of valence electrons aids in predicting how atoms will bond and what ions they might form. To simplify: atoms with fewer than four valence electrons tend to lose them in reactions, while those with more than four tend to gain or share.

Electron Configuration

The electron configuration of an atom provides a roadmap for the location of electrons. It determines how the electrons are distributed among the different orbitals and energy levels. Take the configuration given in the exercise, \(1s^2 2s^2 2p^3\), where we have a total of 5 valence electrons in the second energy level (n=2). This distribution is like the seating arrangement in a theater, where each type of orbital, 's' or 'p', is a different section of seats with a certain capacity.

In the case of our configuration, to achieve the coveted eight electrons, or a 'full house', it needs three more guests or electrons. Remember, the 's' orbital can hold up to two electrons and each 'p' orbital can hold up to six, thus helping us understand the maximum capacity for each level and how many electrons are needed to reach an octet.

Chemical Stability

Chemical stability is the tendency of an atom to maintain its existing electronic structure and resist changes to it. An atom with a full valent shell, generally having eight electrons, is the most chemically stable, as per the octet rule discussed above. This is akin to a state of equilibrium where everything is balanced; no additional electrons are desired, and none wish to be released.

Think of it as building a castle with a stable foundation. Atoms strive for a complete valence shell to minimize energy and maximize stability, just as a fortified castle maintains its structure. Within this metaphor, the stability equates to the castle's ability to withstand invasion or, scientifically speaking, to resist engagement in chemical reactions. Therefore, chemical stability is achieved through the gain, loss, or sharing of electrons to fill the valent shell, just as a castle's strength is ensured by its robust and complete construction.