Scandium (\(\text{Sc}\)) is a metallic element found in the fourth period and the third group of the periodic table, classifying it as the first transition metal. This element is a silvery-white solid often used in high-performance alloys due to its low density and high melting point. Understanding its chemical properties requires determining its basic atomic composition. This article will explain the number of electrons in a neutral scandium atom and detail how those electrons are arranged in its structure.
The Atomic Number Defines the Electron Count
The number of electrons in a scandium atom is determined by its atomic number (\(Z\)). The atomic number represents the exact number of protons found within the nucleus of an atom. Scandium has an atomic number of 21, meaning every scandium atom contains 21 protons.
In its neutral state, an atom carries no net electrical charge because the positive charge of the protons is balanced by the negative charge of the electrons. This fundamental rule dictates that a neutral scandium atom must possess an equal number of electrons to its protons. Consequently, a neutral atom of scandium contains precisely 21 electrons. This count is the basis for all of scandium’s chemical behavior.
How Electrons Are Arranged in Scandium
The 21 electrons in scandium are distributed across four main energy levels, or electron shells, labeled \(K\), \(L\), \(M\), and \(N\). Electrons fill the inner shells first, representing the lowest possible energy state. The first shell (\(K\)) holds two electrons, and the second shell (\(L\)) is completely filled with eight electrons.
The third shell (\(M\)) holds nine electrons in the neutral state, which is characteristic of transition metals. These nine electrons are distributed among the \(3s\), \(3p\), and \(3d\) sub-levels. The first eight electrons fill the \(3s\) and \(3p\) sub-levels, and the ninth electron enters the \(3d\) sub-level.
The final two electrons reside in the fourth shell (\(N\)), specifically in the \(4s\) sub-level. The complete distribution of electrons across the shells is \(2, 8, 9, 2\).
Why Scandium Forms a Trivalent Ion
The chemical reactivity of an atom is determined by its valence electrons, which are the outermost electrons. For scandium, the valence electrons total three: two in the \(4s\) orbital and one in the \(3d\) orbital. Atoms react to achieve a more stable, lower-energy electron configuration, often resembling that of a noble gas.
Scandium achieves this stability by losing all three valence electrons when forming chemical bonds. The two \(4s\) electrons are removed first, followed by the single \(3d\) electron. This loss of three negative charges results in the formation of the positively charged ion \(\text{Sc}^{3+}\).
The \(\text{Sc}^{3+}\) ion possesses 18 electrons, giving it the same electron configuration as the noble gas Argon. This stable configuration, with fully occupied electron shells, is why \(\text{Sc}^{3+}\) is the most common and chemically dominant form of scandium.