Elements with higher atomic numbers tend to be more reactive than those with lower atomic numbers due to a couple of factors:
Increased electron shielding: Elements with higher atomic numbers have more electrons, which leads to increased electron shielding. Electron shielding refers to the repulsion between electrons in different energy levels, reducing the attractive force between the outermost electrons and the nucleus. As a result, the outer electrons are less strongly held by the nucleus, making them more likely to participate in chemical reactions.
Larger atomic size: Elements with higher atomic numbers generally have larger atomic sizes. The increase in atomic size is primarily due to the addition of more electron shells as the atomic number increases. With larger atomic sizes, the outermost electrons are farther away from the nucleus, reducing the attractive force experienced from the positively charged nucleus. Consequently, the outer electrons become more easily involved in chemical reactions, increasing the element's reactivity.
Increased electron-electron repulsion: As the number of electrons in an atom increases, so does the repulsion between electrons. This electron-electron repulsion makes it easier for outermost electrons to be removed or shared during chemical reactions. Therefore, elements with higher atomic numbers are more likely to lose or gain electrons, making them more reactive.
Valence electron configuration: Elements with higher atomic numbers often have more complex electron configurations, resulting in a greater variety of possible valence electron arrangements. This complexity allows for a wider range of bonding possibilities and reactivity. Elements with half-filled or completely filled electron orbitals, such as the noble gases, tend to be less reactive due to their stable configurations.
It is important to note that while higher atomic numbers generally correlate with increased reactivity, there can be exceptions and variations within specific groups or periods of the periodic table due to factors such as electronegativity, ionization energy, and electron affinity.