Question

Use the periodic table to identify the element with each electron configuration. (a) \([\mathrm{Ne}] 3 s^{2} 3 p^{5}\) (b) \([\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{1}\) (c) \([\mathrm{Ar}] 4 s^{2} 3 d^{6}\) (d) \([\mathrm{Kr}] 5 s^{1}\)

Short answer

The elements for each electron configuration are: (a) Chlorine (Cl), (b) Gallium (Ga), (c) Iron (Fe), (d) Rubidium (Rb).

Step-by-step solution

Identify the Element for Configuration (a)

Start with the noble gas \text{[Ne]} which represents the electron configuration up to Neon. Next, add the electrons in the order of the remaining configuration: \(3s^2\) adds two electrons to the s-orbital of the third energy level, and \(3p^5\) adds five electrons to the p-orbital of the third energy level. This configuration corresponds to one less electron than the noble gas Argon \text{[Ar]}, hence the element is Chlorine (Cl).

Identify the Element for Configuration (b)

Start with the noble gas \text{[Ar]} for the electron configuration up to Argon. The order of remaining configuration is \(4s^2\) which fills the s-orbital of the fourth energy level, followed by \(3d^{10}\) which fills the d-orbital of the third energy level, and finally, \(4p^1\) adds one electron to the p-orbital of the fourth energy level. This makes the element Gallium (Ga).

Identify the Element for Configuration (c)

The configuration begins with \text{[Ar]}, representing electrons up to Argon. The electrons are then added to \(4s^2\) filling the s-orbital of the fourth energy level, and \(3d^6\) adds six electrons to the d-orbital of the third energy level. This results in the element Iron (Fe).

Identify the Element for Configuration (d)

Start with the noble gas \text{[Kr]} representing the filled electron configuration up to Krypton. Then, add one electron to the \(5s\) orbital. This results in the element Rubidium (Rb).

Key concepts

Understanding the Periodic Table

The periodic table is a critical tool in chemistry, providing a systematic arrangement of all known elements. It's organized by increasing atomic number, which is the number of protons in an element's nucleus. The table is divided into periods (rows) and groups (columns) that share similar chemical properties.

Key features of the periodic table include:

• Groups (vertical columns) which usually contain elements with similar valence electron configurations, meaning they react similarly.
• Periods (horizontal rows) where elements gain protons and electrons as one moves from left to right, and the shell numbers increase as you move downwards.
• Transition metals, lanthanides, and actinides, which involve the filling of d and f orbitals, creating a variety of oxidation states and properties.

The periodic table also helps predict how an element will interact with others, which is fundamental in identifying an element based on its electron configuration.

Noble Gas Notation Simplifies Electron Configuration

Noble gas notation is a shorthand method to represent an element's electron configuration. This notation uses the nearest noble gas element (group 18 elements), which have complete electron shells and are chemically inert, as a starting reference point. By doing this, you can simplify the representation of the electron configuration for elements with many electrons.

For example, Chlorine's electron configuration could be written in noble gas notation as \[\mathrm{Ne}\] 3s^2 3p^5\. This notation tells us that Chlorine has the same electron configuration as Neon (Ne) plus an additional seven electrons: two in the 3s orbital and five in the 3p orbital. Using noble gas notation can save time and reduce errors, especially when dealing with elements that have a large number of electrons.

Orbital Filling Order and Electron Configuration

Understanding the orbital filling order is necessary to determine an element's electron configuration. Electrons fill orbitals in a way that minimizes energy, following these rules:

• The Aufbau principle dictates that electrons occupy orbitals starting from the lowest available energy levels before moving to higher levels.
• The Pauli exclusion principle states that an orbital can hold a maximum of two electrons, with opposite spins.
• Hund's rule suggests that electrons will fill degenerate orbitals (orbitals with the same energy level) singly as far as possible before pairing up.

These rules create a specific sequence for how orbitals are filled, usually indicated by an arrow diagram or the electron configuration itself. For instance, after the 1s orbital is filled, electrons will fill the 2s orbital, then the 2p orbitals, and so on. This methodical filling order helps to deduce the electron configuration of any element when given its atomic number.

Identifying Elements by Electron Configuration

Identifying elements based on their electron configuration involves understanding the quantum mechanics of electrons in atoms. Each element has a unique electron configuration which can be determined by applying the orbital filling order.

To identify an element, you take the given electron configuration and compare it to the expected configurations based on the periodic table and orbital filling rules. Using the noble gas notation as a shortcut, you can establish which noble gas has been surpassed and then add the extra electrons based on their subshell order. For example, an element with the noble gas notation \[\mathrm{Ar}\] 4s^2 3d^6\ is recognized as iron (Fe) because after the electron configuration of Argon (Ar), six electrons are added to the 3d subshell, and two to the 4s, consistent with iron's known configuration. Recognizing the patterns of electron distribution across the periodic table segments is key in accurately identifying elements.