Valence electrons are the electrons located in the outermost shell of an atom, primarily responsible for forming chemical bonds. These outer shell electrons dictate an element’s chemical behavior and stability. Understanding the count of these electrons is fundamental to predicting an element’s reactivity and the types of compounds it will form. This count reveals the most likely pathways for the atom to achieve a stable electronic configuration.
Understanding Cadmium’s Place
Cadmium (Cd) is a metallic element with an atomic number of 48, meaning a neutral atom contains 48 electrons. Cadmium is situated in Group 12 and Period 5 of the periodic table. Placing it in Group 12 classifies it as a d-block element, alongside zinc and mercury, and it is chemically categorized as a transition metal. Group 12 elements exhibit a characteristic, stable electronic arrangement.
Mapping Cadmium’s Electron Configuration
The arrangement of Cadmium’s 48 electrons follows a specific pattern of orbital filling. Chemists use the noble gas notation, which simplifies the inner shells. For cadmium, the nearest preceding noble gas is krypton (Kr), accounting for the first 36 electrons. The electron configuration for cadmium in its ground state is written as \([Kr] 4d^{10} 5s^2\).
This notation indicates that the remaining 12 electrons fill the higher energy orbitals. Ten electrons completely fill the \(4d\) orbital (\(4d^{10}\)). The final two electrons occupy the outermost \(5s\) orbital (\(5s^2\)). The outermost shell, also known as the valence shell, is determined by the highest principal quantum number present, which is \(n=5\).
The Final Valence Electron Count and Reactivity
Cadmium has two valence electrons, which are the pair found in the \(5s\) orbital. This count is due to the stability of the fully occupied \(4d\) orbital. Although the \(4d\) orbital is located just beneath the \(5s\) orbital, the ten electrons in the \(d\) subshell are highly stable and do not participate in chemical bonding. Therefore, the \(4d^{10}\) electrons are considered part of the core electrons, rather than the chemically active valence electrons.
This count of two valence electrons dictates Cadmium’s chemical reactions. To achieve the most stable configuration, the cadmium atom tends to lose these two outermost \(5s\) electrons. The loss of the two electrons results in the formation of a cation with a charge of positive two, written as \(Cd^{2+}\). This \(+2\) oxidation state is the exclusive charge Cadmium exhibits in its compounds, such as cadmium sulfate (\(CdSO_4\)) and cadmium oxide (\(CdO\)).