Problem 87 - Chemistry The Central Science

Question

Elements in group 7A in the periodic table are called the halogens; elements in group 6A are called the chalcogens. (a) What is the most common oxidation state of the chalcogens compared to the halogens? (b) For each of the following periodic properties, state whether the halogens or the chalcogens have larger values: atomic radii, ionic radii of the most common oxidation state, first ionization energy, second ionization energy.

Step-by-Step Solution

Answer

(a) The most common oxidation state of chalcogens is -2, while for halogens it is -1. (b) - Atomic Radii: Chalcogens > Halogens - Ionic Radii: Chalcogens > Halogens - First Ionization Energy: Chalcogens < Halogens - Second Ionization Energy: Chalcogens < Halogens

Step 1: Determine the most common oxidation state of chalcogens and halogens

To find the oxidation state trend within a group, consider the group numbers and valence electrons. Elements in Group 6A (chalcogens) have 6 valence electrons and tend to gain 2 electrons to complete their octet (stable electron configuration). Therefore, their most common oxidation state is -2. Elements in Group 7A (halogens) have 7 valence electrons, so they tend to gain 1 electron to complete their octet. Hence, their most common oxidation state is -1. Answer (a): Chalcogens = -2; Halogens = -1

Step 2: Compare atomic radii of chalcogens and halogens

To compare atomic radii, consider the general trend of atomic radii in the periodic table. Atomic radii typically increase as we go down a group and decrease as we move from left to right along a period. Since chalcogens are in Group 6A and halogens are in Group 7A, chalcogens have a larger atomic radius as they are located to the left of halogens. Answer (b), Atomic Radii: Chalcogens > Halogens

Step 3: Compare ionic radii of the most common oxidation state of chalcogens and halogens

Groups 6A and 7A elements achieve their most common oxidation states by gaining 2 electrons and 1 electron, respectively. When comparing ionic radii for their most common oxidation states (chalcogens as \(O^{2-}\) and halogens as \(X^{-}\)), both ions gain electrons. Typically, as more electrons are gained, ionic size increases due to increased electron-electron repulsion. As chalcogens gain 2 electrons while halogens only gain 1 electron, chalcogens have a larger ionic radius for their most common oxidation state. Answer (b), Ionic Radii: Chalcogens > Halogens

Step 4: Compare the first ionization energy of chalcogens and halogens

Ionization energy generally increases across a period from left to right and decreases down a group. Since chalcogens (Group 6A) are to the left of halogens (Group 7A), halogens will generally have higher first ionization energies. Answer (b), First Ionization Energy: Chalcogens < Halogens

Step 5: Compare the second ionization energy of chalcogens and halogens

When comparing the second ionization energy, we will deal with removing another electron from each of the chalcogen and halogen ions after their first ionization has occurred. After the first ionization, chalcogens become \(O^{-}\) while halogens become \(X^{2-}\). In this case, it is relatively harder to remove an electron from the negatively charged halogen ion than the chalcogen ion with a single negative charge. Thus, halogens will generally have a higher second ionization energy compared to chalcogens. Answer (b), Second Ionization Energy: Chalcogens < Halogens Finally, here is a summary of the comparisons: (a) Chalcogens have an oxidation state of -2, while halogens have -1. (b) - Atomic Radii: Chalcogens > Halogens - Ionic Radii: Chalcogens > Halogens - First Ionization Energy: Chalcogens < Halogens - Second Ionization Energy: Chalcogens < Halogens

Key Concepts

Oxidation State

The oxidation state of an element indicates how many electrons it tends to gain, lose, or share during a chemical reaction. For chalcogens, which are located in Group 6A of the periodic table, the most common oxidation state is -2. This is because chalcogens have 6 valence electrons and tend to gain 2 electrons to achieve a stable electron configuration, known as the octet.

On the other hand, halogens, which are found in Group 7A, have 7 valence electrons and typically gain 1 electron to complete their octet. This results in their common oxidation state being -1. Understanding the trends in oxidation states helps predict how elements will react in chemical processes and form compounds.

Atomic Radii

Atomic radius is a measure of the size of an atom, from the center of the nucleus to the outermost electron cloud. Within a group on the periodic table, atomic radii increase as you move down the group. This is because additional electron shells are added, making the atom larger.

Along a period from left to right, atomic radii decrease. This is due to the increase in nuclear charge, pulling the electron cloud closer to the nucleus. Therefore, chalcogens, being to the left of halogens, generally have larger atomic radii compared to halogens. This size difference is crucial in understanding the reactivity and bonding behavior of these elements.

Ionic Radii

Ionic radii refer to the size of an ion, which can differ from the atomic radius due to the gain or loss of electrons. When atoms become ions, the number of electrons changes, impacting the size.

• Chalcogens, gaining 2 electrons (e.g., forming an ion like \(O^{2-}\)), possess a larger ionic radius compared to their neutral form.
• Halogens typically gain 1 electron (e.g., forming \(X^{-}\) ions), resulting in an ionic radius that is larger than their atomic radius but smaller than that of chalcogens' ions in their most stable form.

The increase in size when electrons are added is due to increased electron-electron repulsion, which pushes the electron cloud outward. This concept is vital for understanding ionic bonding and why certain elements pursue specific charged states.

Ionization Energy

Ionization energy measures the energy required to remove an electron from an atom or ion. It is an important property that reflects an element's ability to participate in chemical bonding.

- The first ionization energy, when moving from left to right across a period, generally increases due to higher nuclear charge, making it harder to remove an electron. Hence, halogens exhibit higher first ionization energies than chalcogens.- The second ionization energy involves removing a subsequent electron, often from a charged ion formed after the first removal. In this context, halogens, which become negatively charged ions after the first electron removal, present a higher second ionization energy compared to chalcogens.This is because once an ion is negatively charged, it's typically more energetically challenging to remove additional electrons due to increased electron-nucleus attraction, especially for ions like \(X^{2-}\) in halogens versus \(O^{-}\) in chalcogens.