Answer:
In chemistry, the element configuration of an atom refers to the arrangement of its electrons in its outermost energy level, or valence shell. The element configuration is typically written using the symbols of the elements in the periodic table, and it is used to predict the chemical behavior of the atom.
One common way to write element configurations is in terms of noble gas configurations. A noble gas is a chemical element that is unreactive and stable due to its filled valence shell, and the noble gases are helium, neon, argon, krypton, xenon, and radon.
The reason why element configurations are often written in terms of noble gas configurations is that it makes it easier to predict the chemical behavior of the atom. For example, the element configuration of sodium is 1s22s22p63s1. This can be written in terms of the noble gas configuration of neon, which is 1s22s22p6, as [Ne]3s1. This notation indicates that the valence shell of sodium has the same electron configuration as the noble gas neon, plus one additional electron in the 3s subshell.
Similarly, the element configuration of chlorine is 1s22s22p63s23p5. This can be written in terms of the noble gas configuration of argon, which is 1s22s22p6, as [Ar]3d5. This notation indicates that the valence shell of chlorine has the same electron configuration as the noble gas argon, plus five additional electrons in the 3p and 3d subshells.
Therefore, element configurations are written in terms of noble gas configurations to provide a concise and easy-to-understand representation of the electron arrangements in the valence shells of atoms. This can help predict the chemical behavior of the atoms and aid in the understanding of the properties of chemical compounds.