Problem 106 - Chemistry The Molecular Science

Question

Answer these questions about the elements with the electron configurations shown. $$ \mathrm{X}=\left[\begin{array}{ll} \mathrm{Ar}] & 3 d^{\mathrm{s}} 4 s^{2} \end{array} \quad \mathrm{Z}=[\mathrm{Ar}] 3 d^{10} 4 s^{2} 4 p^{5}\right. $$ (a) An atom of which element is expected to have the larger first ionization energy? (b) An atom of which element would be the smaller of the two?

Step-by-Step Solution

Answer

(a) Bromine (Z) has the larger first ionization energy. (b) Bromine (Z) is smaller.

Step 1: Understand Electron Configurations

The element \( \mathrm{X} \) has an electron configuration that starts with \( [\mathrm{Ar}] \ 3d^s \ 4s^2 \). The element \( \mathrm{Z} \) has an electron configuration \( [\mathrm{Ar}] \ 3d^{10} \ 4s^2 \ 4p^5 \). Identify the elements: For \( \mathrm{Z} \), it looks like bromine \((Br)\) due to the full \(3d^{10}\) and partial \(4p^5\) shell. For \( \mathrm{X} \), based on a \(3d^s\), it might have a mistake or require another look, but likely near the beginning of the transition metals.

Step 2: Identify First Ionization Energy Trends

The first ionization energy increases across a period from left to right and decreases down a group. Based on position in the periodic table, \( \mathrm{Z} \) (Bromine) is expected to have a higher ionization energy, being closer to the noble gases and more right in the period.

Step 3: Determine Atomic Size Trend

Atomic size, or atomic radius, decreases across a period from left to right and increases down a group. As atom \( \mathrm{Z} \) is further to the right, it is expected to be smaller than an element \( \mathrm{X} \) earlier in the periodic period.

Key Concepts

Ionization Energy

Ionization energy refers to the amount of energy required to remove an electron from an atom in its gaseous state. The concept is essential in understanding how elements interact chemically.
In the periodic table, ionization energy exhibits a clear trend as you move across a period or down a group.

• Across a Period (Left to Right): Ionization energy generally increases. This trend occurs because atoms have more protons as you move to the right, creating a stronger positive charge. This increased charge attracts the electrons more strongly, making them harder to remove. As a result, elements on the right, like bromine (\(Z\)), usually have higher ionization energies compared to those on the left.
• Down a Group (Top to Bottom): Ionization energy decreases. As you move down a group, atoms have more electron shells, increasing the distance between the nucleus and the outermost electrons. This increased distance weakens the nuclear pull on the outer electrons, making them easier to remove.

Understanding these trends can be immensely helpful in predicting the behavior of elements, such as identifying which element, like bromine, has a higher ionization energy compared to others.

Atomic Size

Atomic size, also referred to as atomic radius, describes the dimensions of an atom from its nucleus to the boundary of its surrounding cloud of electrons. This property is crucial for understanding element properties and predicting interactions.
Atomic size follows discernible trends across the periodic table:

• Across a Period (Left to Right): Atomic size decreases. As more protons add to the nucleus across a period, their increasing positive charge pulls the electron clouds closer, leading to a smaller atomic radius. Thus, elements towards the right, like bromine (\(Z\)), are typically smaller than those on the left.
• Down a Group (Top to Bottom): Atomic size increases. Each subsequent element down a group has an additional electron shell, increasing the overall size of the atom, despite the stronger nuclear charge due to more protons. This added shell outweighs the increased nuclear attraction.

Recognizing these trends will enable you to predict which element between elements like X and Z is smaller or larger based on their position in the periodic table.

Periodic Table Trends

The periodic table is not just a collection of elements but a map to understanding their behaviors and reactions. Periodic table trends are patterns that dictate the arrangement and characteristics of the elements.
These trends help predict how elements might interact and include:

• Ionization Energy Trend: Typically increases across a period (left to right) and decreases down a group. This trend can help quickly assess which elements are more likely to lose or hold onto electrons.
• Atomic Size Trend: Decreases across a period and increases down a group. Understanding this trend helps in recognizing why certain elements, such as those on the far right of a period, display compact sizes compared to their counterparts on the left.
• Electron Affinity and Electronegativity: While not covered in the exercise, these trends often parallel ionization energy, increasing across periods and decreasing down groups. They reflect an atom's tendency to attract electrons.

By understanding these periodic table trends, like those in ionization energy and atomic size, you'll gain insights into why elements such as bromine have the properties they do and how they might react with others. It's these trends that reveal the beautiful order in elemental behaviors.