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, and larger amounts are poisonous. (b) Krypton, Kr. It ranks seventh in abundance of the gases in Earth's atmosphere.

Short answer

(a) As: [Ar] 4s² 3d¹⁰ 4p³; (b) Kr: [Kr].

Step-by-step solution

Find the Atomic Number

For arsenic (As), its atomic number is 33. For krypton (Kr), its atomic number is 36. This information tells us how many electrons each atom has.

Identify the Electron Configuration Order

Electrons fill orbitals in a specific order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, etc. This order must be followed to determine the electron configuration.

Write the Electron Configuration for Arsenic

The electron configuration for arsenic (As) is obtained by filling the orbitals according to the electron filling order up to 33 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³.

Noble Gas Notation for Arsenic

To simplify, we use the previous noble gas, argon (Ar), which represents 1s² 2s² 2p⁶ 3s² 3p⁶. Thus, arsenic's electron configuration in noble gas notation is [Ar] 4s² 3d¹⁰ 4p³.

Write the Electron Configuration for Krypton

The electron configuration for krypton (Kr) fills up to 36 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶.

Noble Gas Notation for Krypton

Krypton's full electron configuration is already that of a noble gas, so it can be left as [Kr] without further abbreviation.

Key concepts

Noble Gas Notation

Noble Gas Notation is a shorthand method for writing electron configurations. By using it, chemists can easily represent the inner-shell electrons of an element without having to write out each sublevel individually. This can be particularly useful for elements with many electrons. For example, instead of writing each sublevel for arsenic, we can use argon (Ar) as a representation because arsenic follows argon in the periodic table. Therefore, the notation [Ar] 4s² 3d¹⁰ 4p³ is used for arsenic.
This simplifies arsenic's electron configuration by incorporating the inner core electrons as part of argon's electron configuration. On the other hand, Krypton is already a noble gas, meaning its full electron configuration matches its "noble" form, and nothing needs to be added. Using noble gas notation helps make the atomic structure more manageable.

Atomic Structure

The atomic structure of an element refers to the arrangement of subatomic particles—protons, neutrons, and electrons—that constitute the atom. Electrons are particularly key when it comes to electron configuration and chemical properties.
Each element has a unique atomic number, which indicates the number of protons and, in a neutral atom, the number of electrons too. In atomic structure, electrons are organized into different energy levels around the nucleus, and within these levels are orbitals that can hold a certain number of electrons. Understanding an element's atomic structure can provide insights into its reactivity, bonding behavior, and position on the periodic table. Importantly, it helps explain why elements like arsenic can be both vital in minor amounts yet toxic in larger doses.

Orbital Filling Order

The orbital filling order is a system used to determine the electron configuration of an atom. Electrons fill orbitals from the lowest to the highest energy level, as described by the Aufbau principle.
This order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, and so on. The principle helps predict how an atom's electron cloud is arranged. Following this sequence, you can identify how electrons occupy these orbitals. For arsenic (atomic number 33), the electrons will fill orbitals up to the 4p sublevel, resulting in its configuration. Krypton, with 36 electrons, fills up to the 4p orbital completely, making it a noble gas.

• The Aufbau principle states electrons will fill lower-energy orbitals before moving to higher ones.
• Hund's Rule asserts that electrons will fill degenerate orbitals singly before pairing up.
• The Pauli Exclusion Principle defines that no two electrons can have the same set of quantum numbers.

Understanding orbital filling is essential for mastering electron configurations.

Arsenic

Arsenic is an element with the atomic number 33. Its electron configuration is pivotal in determining its chemical properties and interactions. Being part of group 15 in the periodic table, arsenic is classified as a metalloid, showing properties of both metals and nonmetals.
Its electron configuration, using noble gas notation, is [Ar] 4s² 3d¹⁰ 4p³. This configuration indicates that arsenic has three electrons in its outermost p orbital, influencing its ability to form chemical bonds.
Arsenic's role in biology and industry is equally notable. In trace amounts, it is essential for growth and development, but larger doses are toxic, making its understanding crucial. Its toxic nature is utilized in pesticides and certain alloys, showcasing its dual beneficial and poisonous characteristics.

Krypton

Krypton is a noble gas, designated by the atomic number 36. Being a noble gas, krypton is known for its lack of reactivity. This is due to its fully filled electron shell, which makes it stable.
The electron configuration for krypton is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶, and when using noble gas notation, it is simply [Kr]. This simplicity highlights its stability and inertness among the periodic table elements.
Krypton finds use in a variety of applications, such as lighting, where it is used in certain types of bulbs, and in science, where its inert properties are valuable. Its abundance in the Earth's atmosphere, while low relative to other gases, makes it an interesting subject of study in atmospheric chemistry as well.