Problem 5 - Chemistry and Chemical Reactivity

Question

Depict the electron configuration for each of the following atoms using spdf and noble gas notations. (a) Arsenic, As. A deficiency of As can impair growth in animals, but larger amounts are poisonous. (b) Krypton, Kr. It ranks seventh in abundance of the gases in Earth's atmosphere.

Step-by-Step Solution

Answer

For Arsenic: \([Ar] \, 4s^2 \, 3d^{10} \, 4p^3\); For Krypton: \([Ar] \, 4s^2 \, 3d^{10} \, 4p^6\).

Step 1: Determine the Atomic Number

For each element, first determine the atomic number, which indicates the number of electrons present. Arsenic (As) has an atomic number of 33, and Krypton (Kr) has an atomic number of 36.

Step 2: Write the Electron Configuration in spdf Notation for Arsenic

For Arsenic, start filling the electron shells in order of increasing energy levels: - 1s: 2 electrons, - 2s: 2 electrons, - 2p: 6 electrons, - 3s: 2 electrons, - 3p: 6 electrons, - 4s: 2 electrons,- 3d: 10 electrons,- 4p: 3 electrons.The full electron configuration for Arsenic is: \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^3 \]

Step 3: Write the Electron Configuration in Noble Gas Notation for Arsenic

The noble gas notation uses the previous noble gas as a starting point. For Arsenic, the previous noble gas is Argon (Ar). Thus, Arsenic's configuration in noble gas notation is:\[ [Ar] \, 4s^2 \, 3d^{10} \, 4p^3 \]

Step 4: Write the Electron Configuration in spdf Notation for Krypton

For Krypton, fill the electron orbitals in order:- 1s: 2 electrons,- 2s: 2 electrons,- 2p: 6 electrons,- 3s: 2 electrons,- 3p: 6 electrons,- 4s: 2 electrons,- 3d: 10 electrons,- 4p: 6 electrons.The full electron configuration for Krypton is:\[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \]

Step 5: Write the Electron Configuration in Noble Gas Notation for Krypton

For Krypton, use the previous noble gas, Argon (Ar), as a reference point. Thus, Krypton's configuration in noble gas notation is:\[ [Ar] \, 4s^2 \, 3d^{10} \, 4p^6 \]

Key Concepts

Noble Gas Notation

In chemistry, noble gas notation is used to simplify writing electron configurations. It involves using the electron configuration of the nearest noble gas before the given element as a starting point. This not only makes the electron configuration shorter but also easier to read and understand.

• The noble gases, such as Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), and Xenon (Xe), have completely filled electron shells.
• For example, in the case of Arsenic, which has the electron configuration \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^3 \], noble gas notation uses Argon (\[ [Ar] \]) to represent all the filled lower energy levels.
• The resulting noble gas notation is \[ [Ar] \, 4s^2 \, 3d^{10} \, 4p^3 \]
• Krypton, similarly, is represented as \[ [Ar] \, 4s^2 \, 3d^{10} \, 4p^6 \].

Applying noble gas notation gives us a streamlined way to write electron configurations, especially for elements with many electrons.

spdf Notation

The spdf notation is a straightforward method to show the arrangement of electrons in an atom. It's named after the types of orbitals that electrons occupy: s, p, d, and f. Each letter represents a specific shape of an electron cloud.

• The 's' orbital can hold a maximum of 2 electrons.
• The 'p' orbital can hold up to 6 electrons.
• The 'd' orbital can accommodate 10 electrons.
• The 'f' orbital can contain up to 14 electrons.

When writing configurations, we fill the orbitals with electrons in increasing order of energy. This is done efficiently using the Aufbau principle, which states that electrons fill low energy orbitals first, followed by higher energy ones.
Applying spdf notation to Arsenic and Krypton, you see the systematic fill:

• Arsenic: \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^3 \]
• Krypton: \[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \]

This notation helps to understand the distribution of electrons among different energy levels and orbitals.

Atomic Number Determination

The atomic number is a fundamental property of an element and is critical in determining electron configurations. It represents the number of protons in an atom’s nucleus and, in a neutral atom, it also indicates the number of electrons. Every element on the periodic table is assigned a unique atomic number.

• For Arsenic (As), the atomic number is 33, so it has 33 electrons.
• Krypton (Kr) has an atomic number of 36, thus it contains 36 electrons.

Knowing the atomic number is essential in writing accurate electron configurations with both noble gas and spdf notations. It dictates how the electrons are arranged within an atom under normal conditions.
Using these principles, determining and understanding electron configurations become straightforward, making it easier to grasp how atoms interact with each other at the atomic level.