Question

Which will experience the greater effective nuclear charge, the electrons in the \(n=3\) shell in Ar or the \(n=3\) shell in \(\mathrm{Kr}\) ? Which will be closer to the nucleus?

Short answer

The electrons in the \(n=3\) shell of Krypton (\(\ce{Kr}\)) will experience a greater effective nuclear charge and will be closer to the nucleus compared to those in the \(n=3\) shell of Argon (\(\ce{Ar}\)). This is because Krypton has more protons (36) than Argon (18), resulting in a stronger attractive force between the nucleus and the electrons in the \(n=3\) shell.

Step-by-step solution

Identify the atomic numbers

Look up the atomic numbers (number of protons in the nucleus) for Argon and Krypton on the periodic table. The atomic number of Argon is 18 and that of Krypton is 36.

Understand the shielding effect

The shielding effect is the reduction in the attractive force between the nucleus and the outer-shell electrons due to the presence of inner-shell electrons. The more shielding effect there is, the less effective nuclear charge the outer electrons will experience. In this case, both Argon and Krypton have electrons in the same shell (n=3), so the shielding effect for both elements will be relatively similar.

Compare the effective nuclear charge

Since Krypton has more protons (36) than Argon (18), the attractive force between the nucleus and the electrons in the n=3 shell will be stronger. Consequently, the electrons in the n=3 shell of Krypton will experience a greater effective nuclear charge compared to those in Argon.

Determine the proximity to the nucleus

Electrons that experience a greater effective nuclear charge are more strongly attracted to the nucleus and are therefore closer to it. In this case, since the electrons in the n=3 shell of Krypton experience a greater effective nuclear charge than those in Argon, they are also closer to the nucleus.

Answer

The electrons in the n=3 shell of Krypton will experience a greater effective nuclear charge and will be closer to the nucleus compared to those in the n=3 shell of Argon.

Key concepts

Atomic Number

The atomic number is a fundamental property of an element that defines its identity in the realm of chemistry. It reflects the number of protons in an element's nucleus and is displayed prominently on the periodic table, functioning as the element's unique identifier. In a neutral atom, the atomic number also reflects the number of electrons swirling around the nucleus, which are responsible for the chemical behavior of the element.

For example, Argon has an atomic number of 18, meaning it has 18 protons in its nucleus and, typically, 18 electrons. Krypton, with an atomic number of 36, has a higher number of protons and corresponding electrons. The atomic number also determines the element's position on the periodic table and allows us to predict properties such as reactivity and electronegativity. In essence, the atomic number is not just a number; it's a key to understanding an element's presence in the universe.

Shielding Effect

The shielding effect describes how electrons in an atom's inner shells provide a 'shield' that diminishes the effective nuclear charge felt by electrons in outer shells. It occurs because these inner electrons repel the outer electrons due to electron-electron repulsion, reducing the net attractive force from the positively charged nucleus.

The strength of the shielding effect can significantly influence an electron's energy and position. It is relatively similar for electrons in the same shell across different elements, yet becomes more pronounced in heavier elements with more electrons. In our case, while the n=3 electrons of Argon and Krypton may experience somewhat similar levels of shielding, Krypton's larger number of protons and electrons contributes to greater complexity in the inter-electronic interactions, nuances that can subtly affect the degree of shielding.

Periodic Table

The periodic table is not just a table; it's the map of the atomic universe. This iconic arrangement of elements in rows (periods) and columns (groups) distills the essence of atomic structure into a comprehensive and predictive tool. Each element on the table is positioned based on its atomic number, electron configuration, and recurring chemical properties.

Elements are organized in order of ascending atomic number from left to right. This organization reveals patterns in element properties, such as metallic character and ionization energy, giving valuable insight into how elements will behave in chemical reactions. Understanding the periodic table thus allows one to infer the relationship between electron arrangements and the forces at play within atoms, such as effective nuclear charge, simply by knowing an element's position.

Electron Shells

Electron shells are like the layers of an onion surrounding the atomic nucleus, each shell housing a set of orbitals in which electrons reside. The nomenclature of these shells begins with the closest to the nucleus being n=1, moving outward incrementally. As n increases, the energy level of the electrons within the shell increases, and they are generally found further from the nucleus.

Electrons within these shells are not only participants in atomic bonding but also pivotal in determining the element's chemical reactivity. In the context of effective nuclear charge, electron shells serve as the arena where the tug-of-war between nuclear attraction and electron shielding plays out. The electrons in the n=3 shell of Krypton, being in the same shell as those in Argon, are influenced by the additional protons and must balance the increased nuclear charge with the inescapable shielding from inner shells.