Final answer:
The electron configuration provided for potassium (K) is in longhand notation as it lists out all of the subshells, whereas the electron configuration for argon (Ar) is in noble-gas notation as it starts with the electron configuration of the noble gas neon (Ne) and lists only the additional electrons.
Step-by-step explanation:
The question asks to identify whether longhand notation or noble-gas notation was used to write the electron configurations of potassium (K) and argon (Ar). Electron configurations can be written in two different notations to describe where the electrons are located around the nucleus of an atom. Longhand notation lists all the subshells and the number of electrons in each, while noble-gas notation abbreviates the configuration by starting with the previous noble gas's electronic structure, followed by the remaining subshells and their electrons.
For potassium (K), the electron configuration given is 1s22s22p63s23p64s1. This is longhand notation because it lists all the orbitals since the first energy level. If potassium were written in noble-gas notation, it would instead be represented as [Ar]4s1, signaling that the electron configuration starts just after the noble gas argon (Ar), followed by the part that is unique to potassium. On the other hand, argon (Ar) is written as [Ne]3s23p6, which is a noble-gas notation because it begins with the abbreviation for neon (Ne), a noble gas, indicating the electronic structure for the first 10 electrons, and then describes only the additional electrons beyond neon's configuration.
When identifying electron configurations, it helps to recognize that the noble-gas notation offers a shortcut by referencing a known configuration of a noble gas, instead of listing every subshell configuration from the beginning of the periodic table. Each noble gas forms the foundation for the next series of elements until the next noble gas is reached, thereby reducing the length and complexity of electron configuration notation for elements with higher atomic numbers.