The Electron Configuration: Ions: Videos & Practice Problems

When elements lose or gain electrons, they form cations and anions, respectively. Cations are positive ions, and when they lose electrons, it occurs from orbitals with the highest principal quantum number (n-value), which indicates the shell number or energy level. For example, electrons are removed from 3p before 3s because it is higher in energy. Anions, on the other hand, are negatively charged ions that gain electrons. These electrons are added to orbitals with available space. In naming anions, the nonmetal base name is retained but ends with "-ide" (e.g., oxide, fluoride, chloride). Understanding the process of electron removal or addition and the resulting ion forms is crucial for grasping ionic compounds and their electron configurations.

Cation Electron Configuration

When elements undergo ionization by losing or gaining electrons, they transform into ions. Cations, which are positively charged ions, are formed when electrons are removed. The process of removing electrons begins with those in the highest principal quantum number, denoted as n. The principal quantum number indicates the shell number or energy level of an electron.

For example, in the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶, the n values correspond to the subshells as follows: 1s has an n value of 1, 2s and 2p have an n value of 2, while 3s and 3p have an n value of 3. To determine which electrons to remove, one should first identify the highest n value. If multiple orbitals share the same n value, the order of removal is based on energy levels, where the orbital listed last has higher energy.

For instance, if we need to remove electrons from 3s and 3p, since 3p is listed after 3s, it possesses more energy and thus, the electron will be removed from the 3p orbital first. The same principle applies to 2s and 2p, where electrons will be removed from 2p before 2s. In summary, always start by identifying the highest n value, and if there are multiple orbitals with the same n, remove electrons from the one listed last.

Cation Electron Configuration Example

To determine the condensed electron configuration for the titanium 3 ion (Ti³⁺), we start by identifying the electron configuration of the neutral titanium atom. Titanium has an atomic number of 22, which means it has 22 electrons. The condensed electron configuration for neutral titanium can be expressed as follows:

Ti: [Ar] 4s² 3d²

In this configuration, [Ar] represents the electron configuration of argon, the nearest noble gas preceding titanium. The next step involves adjusting this configuration to reflect the loss of electrons corresponding to the +3 charge of the titanium ion.

According to the Aufbau principle, when removing electrons, we start with the highest energy level. For titanium, the highest energy level is 4s, followed by 3d. To form the Ti³⁺ ion, we need to remove a total of three electrons:

1. Remove the two electrons from the 4s subshell:

4s² becomes empty.

2. Remove one electron from the 3d subshell:

3d² becomes 3d¹.

Thus, the final condensed electron configuration for the titanium 3 ion is:

Ti³⁺: [Ar] 3d¹

This configuration indicates that the titanium 3 ion has lost three electrons, resulting in a stable electron arrangement.

Anion Electron Configuration

Anions are negatively charged ions formed when an atom accepts one or more electrons. This process involves adding electrons to the available orbitals of the atom. For nonmetals, the naming convention for anions involves retaining the base name of the element while changing the ending to "ide." For example, when oxygen gains electrons, it becomes oxide (O^2-), and when fluorine gains an electron, it becomes fluoride (F^-). Understanding this naming convention is crucial when determining the electron configurations of anions, as it helps identify the specific anion based on its elemental origin.

Anion Electron Configuration Example

The nitride ion, represented as N^3-, is derived from nitrogen, which is located in group 3A of the periodic table. The negative charge of -3 indicates that the nitride ion has gained three additional electrons. To determine its full electron configuration, we first need to establish the configuration for neutral nitrogen, which has an atomic number of 7. The electron configuration for neutral nitrogen is:

1s² 2s² 2p³

Next, we account for the three extra electrons gained by the nitride ion. The 1s and 2s orbitals are already filled to their maximum capacity of 2 electrons each, so they remain unchanged:

1s² 2s²

The 2p orbital can hold up to 6 electrons, and since it currently has 3, we can add the 3 additional electrons to fill it completely. Thus, the 2p configuration becomes:

2p⁶

Combining these, the full electron configuration for the nitride ion is:

1s² 2s² 2p⁶

This configuration indicates that the nitride ion now has the same electron configuration as the noble gas neon, which is a stable configuration. Therefore, while the full electron configuration is the most complete answer, it is also valid to note that the nitride ion shares its electron configuration with neon, represented in shorthand as:

[Ne]

What is the full electron configuration of the selenide ion?

• A. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴
• B. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶
• C. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴ 5s²
• D. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸ 4p⁴ 5s² 5p²

Answer: (B)

Determine the electron configuration for the Cl⁺ ion.

• A. [Ne] 3s¹ 3p⁵
• B. [Ne] 3s² 3p⁶
• C. [Ne] 3s² 3p⁵
• D. [Ne] 3s² 3p⁴

Answer: (D)

Determine the electron configuration and electron orbital diagram for the silver ion.

• A. [Kr] 4d¹⁰
• B. [Kr] 4d⁸ 5p²
• C. [Kr] 4d⁸
• D. [Kr] 4d⁸ 5s²

Answer: (A)

Here’s what students ask on this topic:

How do you write electron configuration for ions?

Writing electron configurations for ions involves the same principles as for neutral atoms, but you must account for the gain or loss of electrons due to the ion's charge. Here's how to do it:

1. Determine the number of electrons in the ion. For cations (positively charged ions), subtract the charge from the atomic number to find the number of electrons. For anions (negatively charged ions), add the charge to the atomic number.
2. Write the electron configuration for the neutral atom. Use the periodic table to determine the order in which the orbitals fill up (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.).
3. Adjust the electron configuration for the ion. If it's a cation, remove electrons starting from the highest energy level (outermost shell). If it's an anion, add electrons to the next available orbital in the sequence.

For example, for Na⁺ (sodium ion), the neutral sodium atom has 11 electrons, but Na⁺ has lost one electron, leaving it with 10 electrons. The electron configuration for Na⁺ is the same as that for neon (Ne), a noble gas: 1s² 2s² 2p⁶. For Cl^- (chloride ion),

What is the term for two different ions with the same electron configuration?

The term for two different ions with the same electron configuration is "isoelectronic." Isoelectronic species are atoms, molecules, or ions that have the same number of electrons and hence the same electronic structure. This can occur despite them having different numbers of protons or being different elements altogether. A classic example of isoelectronic ions would be the sodium cation (Na⁺) and the neon atom (Ne), both of which have ten electrons and thus share the same electron configuration of:

${\mathrm{1s}}^2{\mathrm{2s}}^2{\mathrm{2p}}^6$

However, they differ in their nuclear charges, with sodium having 11 protons and neon having 10 protons. Isoelectronic species often exhibit similar chemical and physical properties due to their analogous electron arrangements.