Ions and the Octet Rule: Videos & Practice Problems

Main group elements strive for stability by achieving a filled outer shell of 8 valence electrons. Metals, like sodium, lose electrons to resemble the noble gas preceding them, while nonmetals, such as sulfur, gain electrons to mimic the following noble gas. This electron transfer leads to the formation of cations and anions, enhancing stability and reducing reactivity. For cations, electrons are removed from the highest shell number first, following the order of subshells. Understanding these principles is crucial for grasping chemical reactivity and the formation of ionic compounds.

Ions and the Octet Rule Concept 1

The tendency of main group elements to achieve a stable electron configuration, typically characterized by having eight valence electrons, drives their chemical reactivity. Main group metals, such as sodium, tend to lose electrons to resemble the noble gas preceding them in the periodic table. For instance, sodium (atomic number 11) aims to lose one electron to match the electron configuration of neon (atomic number 10), resulting in a stable configuration with 10 electrons.

Conversely, main group nonmetals, like sulfur, generally gain electrons to emulate the noble gas that follows them. Sulfur, with an atomic number of 16, seeks to gain two electrons to achieve the electron configuration of argon (atomic number 18). This process leads to fully filled s and p subshells, which enhances stability and reduces chemical reactivity.

For example, consider lithium and fluorine. Lithium has the electron configuration of 1s² 2s¹, with one electron in its outer shell. Fluorine, on the other hand, has the configuration 1s² 2s² 2p⁵, indicating it has seven electrons in its second shell. Lithium will lose its one outer electron, filling its s subshell and achieving a configuration similar to helium. Meanwhile, fluorine gains that electron, becoming negatively charged and filling its p subshell to reach a configuration akin to neon (2p⁶). This electron transfer results in both lithium and fluorine forming ions that mimic the stable configurations of nearby noble gases.

The stability of noble gases, attributed to their filled outer shells, is the ultimate goal for these elements during chemical reactions. By achieving similar electron configurations, main group elements can attain greater stability and lower their reactivity.

Ions and the Octet Rule Example 1

To determine how many electrons a magnesium atom must lose to achieve a filled outer shell, we start by examining its atomic structure. Magnesium has an atomic number of 12, which indicates it has 12 electrons. The electron configuration of magnesium is represented as 1s² 2s² 2p⁶ 3s². This configuration shows that magnesium has two electrons in its outermost shell (the 3s subshell).

In order to attain a stable electron configuration similar to that of the nearest noble gas, neon, which has an atomic number of 10 and an electron configuration of 1s² 2s² 2p⁶, magnesium must lose its two outermost electrons. By losing these 2 electrons, magnesium will have a total of 10 electrons, mirroring the electron configuration of neon.

Thus, magnesium must lose 2 electrons to achieve a filled outer shell, aligning its electron configuration with that of a noble gas. This tendency to lose electrons is characteristic of metals, which strive to attain stability by resembling the electron configurations of noble gases that precede them in the periodic table.

Ions and the Octet Rule Concept 2

When dealing with metal cations, the process of electron removal follows a specific order based on the principal quantum number, denoted as n. The n value indicates the shell number or energy level of the electrons. For instance, in the electron configuration of an atom, such as 1s², 2s², 2p⁶, 3s², and 3p⁶, the numbers preceding the subshell letters (s and p) correspond to the n values.

In this example, the 1s² electrons are in the first shell where n equals 1, while the 2s² and 2p⁶ electrons are in the second shell where n equals 2. Similarly, the 3s² and 3p⁶ electrons are located in the third shell where n equals 3.

When forming a cation, electrons are removed starting from the highest shell number. Therefore, if we begin to remove electrons, we would first target the 3p⁶ electrons before addressing the 3s² electrons. This systematic approach ensures that electrons are removed in the order of their energy levels, prioritizing those in the outermost shell.

Ions and the Octet Rule Example 2

To write the condensed electron configuration for the sodium ion (Na⁺), we start by determining the electron configuration of neutral sodium, which has an atomic number of 11. This means that the electron configuration for neutral sodium is:

1s² 2s² 2p⁶ 3s¹

Next, to form the sodium ion, we need to remove one electron, as indicated by the +1 charge. When removing electrons to form a cation, we always start with the highest energy level. In this case, the highest shell is n=3, which corresponds to the 3s orbital. By removing the single electron from the 3s subshell, we are left with:

1s² 2s² 2p⁶

This configuration matches that of neon (Ne), which has an atomic number of 10. Therefore, the condensed electron configuration for the sodium ion can be expressed as:

[Ne]

This notation indicates that the sodium ion has the same electron configuration as neon, making it the most condensed and acceptable representation. While it is technically possible to represent the configuration as [He] for the 1s² portion, the preferred and more common method is to use [Ne] to reflect the complete configuration of the sodium ion.

Ions and the Octet Rule Example 3

To determine the full electron configuration of the nitride ion (N^3-), we start with the neutral nitrogen atom, which has an atomic number of 7. The electron configuration for neutral nitrogen is:

1s² 2s² 2p³

Next, since the nitride ion has gained three additional electrons, we need to add these electrons to the available orbitals. The 1s orbital is already filled with 2 electrons, and the 2s orbital is also filled with 2 electrons. The 2p orbital can hold up to 6 electrons, and since it currently has 3 electrons, we can add the 3 additional electrons there.

Thus, the complete electron configuration for the nitride ion becomes:

1s² 2s² 2p⁶

This configuration indicates that the nitride ion has achieved a stable electron arrangement similar to that of neon, which is a noble gas. However, it is important to note that the question specifically requests the full electron configuration rather than the condensed version.

Determine the electron configuration for the Cl^– ion.

• A.
• B.
• C.
• D.
• E.

Answer: (C)

Here’s what students ask on this topic:

What is the octet rule and why is it important in chemistry?

The octet rule states that atoms tend to gain, lose, or share electrons to achieve a full set of eight valence electrons, resembling the electron configuration of noble gases. This rule is crucial because it explains the stability of noble gases and the reactivity of other elements. By achieving an octet, atoms lower their energy and become more stable. This principle helps predict the formation of ions and the types of bonds atoms will form, which is fundamental in understanding chemical reactions and the properties of compounds.

How do metals and nonmetals achieve a stable electron configuration?

Metals achieve a stable electron configuration by losing electrons to form cations, thereby resembling the noble gas that precedes them in the periodic table. For example, sodium (Na) loses one electron to have the same electron configuration as neon (Ne). Nonmetals, on the other hand, gain electrons to form anions, mimicking the noble gas that follows them. For instance, sulfur (S) gains two electrons to achieve the electron configuration of argon (Ar). This electron transfer results in filled outer shells, enhancing stability and reducing reactivity.

Why do noble gases have low chemical reactivity?

Noble gases have low chemical reactivity because they possess a complete set of valence electrons, typically eight, which makes their outer electron shell fully filled. This stable electron configuration means they have little tendency to gain, lose, or share electrons, resulting in minimal chemical reactivity. Their stability is a key reason why other elements strive to achieve a similar electron configuration through the gain or loss of electrons, as described by the octet rule.

How are electrons removed from metal cations?

When forming metal cations, electrons are removed from the highest shell number first, which corresponds to the highest principal quantum number (n). For example, in the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶, electrons would be removed from the 3p subshell before the 3s subshell. This order ensures that electrons are taken from the outermost energy level, which is the least stable and most easily lost, leading to the formation of a positively charged ion.

What is the significance of achieving a noble gas electron configuration?

Achieving a noble gas electron configuration is significant because it leads to greater stability for the atom or ion. Noble gases are inherently stable due to their filled valence shells, which means they have minimal chemical reactivity. When other elements gain or lose electrons to achieve a similar configuration, they also attain a lower energy state and increased stability. This concept is fundamental in understanding why atoms form ions and how ionic compounds are created, as it explains the driving force behind chemical reactions and bonding.