Question

What is the noble gas core? How does it simplify the writing of electron configurations?

Short answer

The noble gas core represents the electron configuration of the nearest noble gas with fewer electrons, indicating its full valence electron shell. It simplifies the writing of electron configurations by allowing us to summarize core electrons with the symbol of the previous noble gas in the periodic table, such as [Ne]3s²3p⁵ for Chlorine instead of writing out the full configuration.

Step-by-step solution

Defining the Noble Gas Core

A noble gas core represents the electron configuration of the previous noble gas. Noble gases have a full valence electron shell making them very stable. By using a noble gas core, we can show only the outer electrons (the valence electrons) of an atom, which are the ones involved in chemical reactions.

Electron Configurations

Electron configurations describe the arrangement of electrons in an atom. The full electron configuration of an atom can be lengthy to write out, especially for atoms with many electrons. For instance, the electron configuration of Chlorine (17 electrons) is written as 1s²2s²2p⁶3s²3p⁵.

Simplifying Electron Configurations with the Noble Gas Core

Using the noble gas core can greatly simplify the writing of electron configurations. We identify the noble gas that precedes the atom in question and use its symbol in brackets to represent the core electrons. For example, Chlorine is preceded by the noble gas Neon (10 electrons: 1s²2s²2p⁶). So, the shorthand electron configuration for Chlorine becomes [Ne]3s²3p⁵, indicating that Chlorine has the same core electron configuration as Neon with the addition of five more electrons in the 3rd shell.