The chemical element Lead, represented by the symbol Pb, is a dense, soft metal. A neutral atom of Lead possesses a specific and fixed number of electrons determined by its atomic number, which is 82. This number corresponds directly to its unique position on the periodic table.
The Total Number of Electrons
The identity of any element is defined by its atomic number (Z). For Lead, Z equals 82, signifying that every Lead atom contains 82 protons within its nucleus. This is the highest atomic number for any stable element.
In a neutral atom, the total number of electrons must perfectly balance the positive charge of the protons. Therefore, a neutral atom of Lead contains a total of 82 electrons. Lead is located in Group 14 and Period 6 of the periodic table.
How Electrons Are Arranged in Shells
The 82 electrons in a Lead atom occupy a complex series of energy levels and sublevels, known as the electron configuration. This configuration describes the exact orbital path for every electron, starting from the lowest energy level closest to the nucleus. The complete distribution is written as \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 4f^{14} 5s^2 5p^6 5d^{10} 6s^2 6p^2\).
A more compact way to represent this is using the noble gas shorthand notation, which summarizes the inner, core electrons. For Lead, this is [Xe] \(4f^{14} 5d^{10} 6s^2 6p^2\), where [Xe] represents the configuration of the noble gas Xenon, which accounts for 54 of the 82 electrons. When viewed by principal shells, the 82 electrons are distributed as 2, 8, 18, 32, 18, 4 in the first through sixth shells, respectively.
Valence Electrons and Chemical Behavior
The outermost electrons, known as valence electrons, are those most involved in chemical bonding and reactions. For Lead, these are the electrons in the highest principal energy level, which is the sixth shell. The valence electron configuration is \(6s^2 6p^2\), meaning Lead has a total of 4 valence electrons.
These four electrons reside in both the \(s\) and \(p\) orbitals of the sixth shell, classifying Lead as a p-block element and a post-transition metal. The arrangement of these valence electrons dictates the chemical properties of Lead, including the number of bonds it can form. The presence of electrons in the \(s\) and \(p\) orbitals gives Lead the potential to participate in reactions that involve the loss of two or all four of these outer electrons.
How Lead Forms Ions
A neutral Lead atom with 82 electrons will change its electron count when it forms a chemical bond and becomes an ion. Lead typically forms positively charged ions, or cations, by losing its valence electrons. The most common ionic form is \(\text{Pb}^{2+}\), which is created when the atom loses the two electrons from its \(6p\) orbital. This loss of two electrons leaves the ion with 80 total electrons.
Lead can also form the \(\text{Pb}^{4+}\) ion, which requires the loss of all four valence electrons, resulting in an ion with 78 electrons. However, the \(\text{Pb}^{2+}\) state is significantly more stable for Lead compared to the \(\text{Pb}^{4+}\) state. This preference is explained by the inert pair effect, where the \(6s^2\) pair of electrons in heavy elements like Lead is held more tightly by the nucleus and is less likely to participate in chemical bonding.