Problem 68 - Chemistry The Central Science In Si Units

Question

Copper and calcium both form +2 ions, but copper is far less reactive. Suggest an explanation, taking into account the ground-state electron configurations of these elements and their atomic radii.

Step-by-Step Solution

Answer

Copper is less reactive due to its filled 3d subshell and smaller atomic radius compared to calcium.

Step 1: Determine Electron Configurations

Copper (\( \text{Cu} \)) has an atomic number of 29, while calcium (\( \text{Ca} \)) has an atomic number of 20. Their electron configurations are: - Copper: [Ar] 3d\(^ {10}\) 4s\(^ {1}\)- Calcium: [Ar] 4s\(^ {2}\).Copper has a filled \( 3d \) subshell, making it more stable, while calcium has a complete \( 4s \) subshell, which can be easily lost leading to higher reactivity.

Step 2: Compare Atomic Radii

The atomic radius refers to the size of atoms. Copper has a smaller atomic radius compared to calcium. This is because copper has more protons, which increases the nuclear charge and pulls the electron cloud closer. Therefore, electrons are held more tightly in copper than in calcium, making copper less reactive.

Step 3: Relate Reactivity to Ion Formation

In forming \( +2 \) ions, copper loses its \( 4s \) and \( one 3d \) electrons while calcium loses its \( 4s \) electrons. Copper's smaller radius and filled \( 3d \) subshell make it less willing to lose electrons, whereas calcium's electrons are farther from the nucleus and more easily lost, explaining its greater reactivity.

Key Concepts

Atomic Radii Explained

The atomic radius is a crucial factor in understanding the properties of elements. It essentially represents the size of an atom, measured from the nucleus to the outer boundary of its electron cloud. This size can significantly influence how an element behaves chemically.

When we compare the atomic radii of copper and calcium, copper has a smaller radius. This difference arises because copper has 29 protons, whereas calcium only has 20. More protons mean a stronger positive charge in the nucleus. This increased charge pulls the surrounding electrons closer to the nucleus, resulting in a smaller radius for copper.

In contrast, calcium's fewer protons exert less pull on the electron cloud, allowing the electrons to exist in a larger space. This larger atomic radius means that the valence electrons in calcium are further away from the nucleus and are not held as tightly. This physical separation makes it easier for calcium to react with other substances.

Reactivity of Elements

Understanding why some elements are more reactive than others can be guided by looking at their electron configurations and atomic structures. Reactivity is how likely an element is to participate in chemical reactions. An element's reactivity is influenced by how easily it can lose or gain electrons.

Copper and calcium, for example, exhibit differing levels of reactivity due to their electron configurations. Copper has a filled 3d subshell after losing its 4s electron, whereas calcium typically loses its 4s electrons. The stable electron configuration of copper's filled d subshell makes it less reactive.

Elements with a full or half-full subshell tend to be more stable and therefore less reactive. On the other hand, elements like calcium that can readily lose electrons, usually from their outermost s subshell, are more reactive. As a result, even though both copper and calcium form +2 ions, calcium is considerably more reactive due to how easily it can lose its outer electrons.

Ion Formation

Ion formation is a key concept in understanding the chemical reactions and behaviors of elements. It involves the loss or gain of electrons by atoms to achieve a more stable electron configuration, often resembling that of the noble gases.

When looking at copper and calcium, both elements form +2 ions, but the process and ease with which this happens differ. Copper loses its 4s electron and one of its 3d electrons to form a +2 ion. This electron loss is somewhat resisted due to copper's filled 3d subshell. Meanwhile, calcium easily loses its two 4s electrons because they are further from the nucleus and less tightly bound.

This distinction in how elements form ions connects back to their atomic radii and electron configurations. In elements with larger atomic radii like calcium, the outer electrons experience less attraction to the nucleus, facilitating their removal and leading to higher reactivity. In copper, the smaller radius and the stability offered by a filled 3d subshell contribute to its less frequent ion formation.