Ions and the Octet Rule: Videos & Practice Problems

Main group elements strive for a stable electron configuration by achieving 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 filled s and p subshells, enhancing stability and reducing reactivity. For instance, lithium loses one electron, and fluorine gains one, resulting in ions with configurations similar to noble gases, which are inherently stable due to their filled outer shells.

Ions and the Octet Rule Concept 1

The tendency of main group elements to achieve a stable electron configuration, often resembling that of noble gases, drives their chemical reactivity. Main group metals typically lose electrons to attain the electron configuration of the nearest preceding noble gas. For instance, sodium (Na), with an atomic number of 11, seeks to lose one electron to match the electron count of neon (Ne), which has an atomic number of 10. By losing this electron, sodium achieves a stable configuration with 10 electrons.

Conversely, main group nonmetals tend to gain electrons to emulate the electron configuration of the nearest following noble gas. Taking sulfur (S) as an example, it has an atomic number of 16 and aims to gain two electrons to resemble argon (Ar), which has an atomic number of 18. This gain results in sulfur having 18 electrons, thus achieving stability.

The underlying reason for these electron transfers is the desire to fill the s and p subshells, leading to greater stability and reduced chemical reactivity. For example, lithium (Li) has the electron configuration of 1s² 2s¹, with one electron in its outer shell. Fluorine (F), on the other hand, has the configuration of 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 (He), which is stable with 2 electrons.

Fluorine, upon gaining the electron from lithium, becomes negatively charged and its configuration changes to 1s² 2s² 2p⁶, filling its p subshell. This configuration mirrors that of neon (Ne), which is stable with 10 electrons in total. Thus, both lithium and fluorine transform into ions that reflect the stable electron configurations of their respective noble gases, highlighting the fundamental goal of achieving filled outer shells for enhanced stability.

Ions and the Octet Rule Example 1

Magnesium, with an atomic number of 12, has an electron configuration of 1s² 2s² 2p⁶ 3s². To achieve a filled outer shell, magnesium must lose electrons. The goal is to attain a stable electron configuration similar to that of the nearest noble gas, which is neon, having an atomic number of 10 and an electron configuration of 1s² 2s² 2p⁶.

Since magnesium has two electrons in its outermost shell (the 3s subshell), it can achieve a filled outer shell by losing these two electrons. This process results in a stable electron configuration that mirrors that of neon. Therefore, magnesium must lose 2 electrons to obtain a filled outer shell, aligning its electron configuration with that of a noble gas.

Ions and the Octet Rule Concept 2

When dealing with metal cations, the process of electron removal begins with the electrons located in the highest principal energy level, denoted by the quantum number 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 3p⁶, the numbers preceding the subshell letters (s and p) represent the n values. Here, 1s² indicates that the electrons are in the first shell (where n = 1), while 2s² and 2p⁶ indicate that the electrons are in the second shell (where n = 2). Similarly, 3s² and 3p⁶ show that the electrons are in the third shell (where n = 3).

When forming a cation, the electrons are removed starting from the highest shell number. Therefore, if we were to remove electrons from the configuration mentioned, we would first target the 3p electrons before removing any from the 3s subshell. This systematic approach ensures that the electrons are removed in the correct order, reflecting their energy levels and stability.

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. 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, we always start from 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 a complete octet. 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 stable and is the most accepted way to represent the configuration of Na⁺.

Ions and the Octet Rule Example 3

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

1s² 2s² 2p³.

When nitrogen gains three electrons to form the nitride ion, we need to add these electrons to the available orbitals. The 1s and 2s orbitals are already filled, with the 1s holding 2 electrons and the 2s holding 2 electrons. The 2p orbital can accommodate up to 6 electrons, and since it currently has 3 electrons, we can add the additional 3 electrons there.

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

1s² 2s² 2p⁶.

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

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 in chemistry?

The octet rule in chemistry states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons, similar to the noble gases. This rule is particularly applicable to main group elements. For example, sodium (Na) loses one electron to resemble neon (Ne), while sulfur (S) gains two electrons to mimic argon (Ar). This electron arrangement leads to filled s and p subshells, enhancing the atom's stability and reducing its reactivity.

How do metals and nonmetals achieve stable electron configurations?

Metals achieve stable electron configurations by losing electrons to resemble the noble gas preceding them in the periodic table. For instance, sodium (Na) loses one electron to have the same electron configuration as neon (Ne). Nonmetals, on the other hand, gain electrons to mimic the noble gas following them. For example, sulfur (S) gains two electrons to achieve the electron configuration of argon (Ar). This process results in filled s and p subshells, which enhances stability and reduces reactivity.

Why do noble gases have low reactivity?

Noble gases have low reactivity because they possess a completely filled outer electron shell, typically with eight valence electrons. This stable electron configuration minimizes their tendency to gain, lose, or share electrons, making them chemically inert. For example, neon (Ne) has a full 2s²2p⁶ configuration, which makes it highly stable and unreactive under normal conditions.

What happens to the electron configuration of lithium when it loses an electron?

When lithium (Li) loses an electron, it forms a Li⁺ ion. The original electron configuration of lithium is 1s²2s¹. By losing one electron, it achieves the configuration 1s², which is similar to the noble gas helium (He). This loss of an electron results in a filled 1s subshell, enhancing the stability of the lithium ion.

How do you determine which electrons are removed first when forming a metal cation?

When forming a metal cation, electrons are removed from the highest principal quantum number (n) first. For example, in the electron configuration 1s²2s²2p⁶3s²3p⁶, the electrons in the 3rd shell (n=3) are removed before those in the 2nd shell (n=2). Within the same shell, electrons are removed from the p subshell before the s subshell. Therefore, 3p electrons are removed before 3s electrons.