Ions and the Octet Rule (Simplified): Videos & Practice Problems

The tendency of main group elements to achieve a stable configuration of eight valence electrons, known as the octet rule, drives their chemical reactivity. Main group metals, such as sodium, typically lose electrons to resemble the noble gas preceding them in the periodic table. For example, sodium (atomic number 11) aims to lose one electron to attain the electron configuration of neon (atomic number 10), resulting in a stable, filled outer shell.

Conversely, nonmetals like chlorine (atomic number 17) gain electrons to emulate the noble gas that follows them. Chlorine needs to gain one electron to achieve the electron configuration of argon, thereby completing its outer shell. This behavior of gaining or losing electrons is motivated by the desire to create fully filled energy levels, which enhances stability and reduces chemical reactivity.

To illustrate, consider lithium and fluorine. Lithium has one valence electron, represented by the electron configuration 2-1, while fluorine has seven valence electrons, with a configuration of 2-7. As a group 1A element, lithium loses its single valence electron, becoming a lithium ion (Li⁺) with a filled outer shell, similar to helium. The lost electron is transferred to fluorine, which then becomes a fluoride ion (F^-) after gaining that electron, achieving a filled outer shell akin to neon.

In summary, the interactions between metals and nonmetals in the context of the octet rule highlight their tendency to gain or lose electrons to attain the electron configurations of the nearest noble gases, thereby achieving greater stability.

To determine how many electrons a sodium atom must move to achieve a filled outer shell, we first examine its atomic structure. Sodium, with an atomic number of 11, has 11 electrons. The electron configuration of sodium is 1s² 2s² 2p⁶ 3s¹, indicating that it has one electron in its outermost shell (the third shell).

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 a complete outer shell (1s² 2s² 2p⁶), sodium must lose one electron. By losing this single electron from its outer shell, sodium will have 10 electrons remaining, thus achieving a filled outer shell.

Therefore, the sodium atom must move one electron to obtain a filled outer shell, aligning with the behavior of metals that typically lose electrons to resemble the electron configurations of noble gases.

When determining the electron arrangement for a metal cation, such as the calcium ion (Ca²⁺), it is essential to understand that cations are positively charged ions formed by the loss of electrons. Calcium has an atomic number of 20, indicating it has 20 electrons in its neutral state. The electron configuration for neutral calcium can be expressed as follows: it has 2 electrons in the first shell, 8 in the second shell, 8 in the third shell, and 2 in the fourth shell, which can be summarized as 2-8-8-2.

To derive the electron arrangement for the Ca²⁺ ion, we need to remove electrons from the highest energy level. In this case, the highest energy level corresponds to the fourth shell, where the 2 electrons are located. By removing these 2 electrons, the charge of the ion increases by +2, resulting in the electron configuration of the calcium ion being 2-8-8.

This process highlights the importance of understanding electron arrangements and the behavior of electrons in forming ions. Remember, each electron removed contributes to the overall positive charge of the ion, and the configuration reflects the distribution of electrons across the various energy levels.

To understand the electron arrangement of the nitride ion (N^3-), we start with the neutral nitrogen atom, which has an atomic number of 7. This means it has 7 electrons. The electron configuration for neutral nitrogen can be represented as follows: the first shell holds 2 electrons, and the second shell holds the remaining 5 electrons. Therefore, the electron arrangement for neutral nitrogen is 2-5.

When we consider the nitride ion (N^3-), the negative charge indicates that the atom has gained 3 additional electrons. To accommodate these extra electrons, we follow these steps:

1. The first shell is already full with 2 electrons and cannot hold any more.

2. The second shell can hold up to 8 electrons. Since it currently has 5 electrons, we can add the 3 additional electrons gained from the ionization process.

As a result, the electron arrangement for the nitride ion becomes 2-8. This configuration indicates that the nitride ion is stable, with a full outer shell, which is characteristic of nonmetals gaining electrons to achieve a noble gas configuration.