Question

Two elements, \(A\) and \(B\), have the electron configurations shown. $$ \mathrm{A}=[\mathrm{Kr}] 4 s^{2} \quad \mathrm{B}=[\mathrm{Ar}] 3 d^{10} 4 s^{2} 4 p^{5} $$ (a) Which element is a metal? (b) Which element has the greater ionization energy? (c) Which element has the larger atomic radius? (d) Which element has the greater electron affinity?

Short answer

(a) B is the metal. (b) A has a greater ionization energy. (c) A has a larger atomic radius. (d) B has a greater electron affinity.

Step-by-step solution

Identify the element is a metal

The rule is that any atom with an unfilled electron shell is considered a metal. Element A has an electron configuration: [Kr] 4 s^2. Element B has an electron configuration: [Ar] 3d^10 4s^2 4p^5. B ended at 4p^5, it has an unfilled shell, so, B is a metal.

Determine which element has a greater ionization energy

Ionization energy is the energy required to remove an electron from a neutral atom in its gaseous phase. Elements with a greater atomic number and a full outer shell will have a higher ionization energy since they are more stable in nature. Here, A has a full outer shell, so A has a greater ionization energy.

Determine the element with a larger atomic radius

Atomic radius decreases across a period on the periodic table and increases down a group. This is because when you move down the groups, there are more electron shells. Here, A with configuration [Kr] 4 s^2 is presumed to have a larger atomic radius compared to B since it likely belongs to a lower period.

Establish the element with a greater electron affinity

Electron affinity is the amount of energy released when electrons are added to a neutral atom to form a negative ion. Elements that do not have a full outer shell tend to have a higher electron affinity since they can experience stability once there are enough electrons to fill their outer shell. In this case, B with an unfilled shell (having its electron configuration end in 4p^5) would have a higher electron affinity as it is closer to filling its outer shell than A.

Key concepts

Electron Configuration

Understanding electron configuration helps us determine the distribution of electrons in an atom’s orbitals. For element A, with [Kr] 4s², we see it belongs to the same group as Krypton. It has a filled outer s subshell, making it stable.
Element B has the electron configuration [Ar] 3d¹⁰ 4s² 4p⁵. It ends in 4p⁵, indicating it's just one electron short of a full p orbital. This makes it chemically reactive and an eager participant in reactions. Electron configurations offer insights into reactivity, stability, and the element's characteristics.

• Filled outer shells indicate stability.
• Incomplete outer shells suggest reactivity.

Periodic Trends

Periodic trends explain how the periodic table's layout reflects various elemental properties. As we move across a period, ionization energy increases, and atomic radius decreases. These trends occur due to effective nuclear charge experiences by electrons.
In our exercise:

• Element B, with [Ar] 3d¹⁰ 4s² 4p⁵, shows it’s across from element A, explaining its smaller radius.
• Element A, further down the group, means larger atomic radius.
• Trends help predict and understand chemical behavior.

By analyzing these trends, we can predict and understand properties such as ionization energy and atomic size.

Ionization Energy

Ionization energy is key to understanding an element's tendency to lose electrons. It refers to the energy required to remove an electron from an atom. High ionization energy means it's difficult to remove electrons, indicating tight hold by the nucleus.
For element A, its full outer shell mirrors higher ionization energy due to stability. Element B’s configuration shows it's more reactive, so its ionization energy would be lower.

• Higher ionization energy indicates a stable, less reactive atom.
• Elements with near-full shells exhibit higher ionization.

Ionization energy offers insights into an atom’s reactivity and its chemical interactions.

Atomic Radius

Atomic radius describes the size of an atom. The size impacts how atoms interact in chemical reactions. A larger radius means less tight electron gripping by the nucleus.
Element A has [Kr] 4s², suggesting it's further down the group, giving it a larger atomic radius. B, on the other hand, has a smaller radius because it’s completing a period.

• Larger atoms often lose electrons easily.
• Atomic radius influences bonding and stability.

By understanding radius patterns, we can anticipate interactions between elements.

Electron Affinity

Electron affinity measures how much an atom wants to gain electrons. It's the energy change when an electron is added to a neutral atom, forming an anion.
Element B, with configuration [Ar] 3d¹⁰ 4s² 4p⁵, is eager to add an electron to complete its 4p orbital. This eagerness reflects in its high electron affinity compared to A. Stability increases when outer shells are complete.

• High electron affinity indicates readiness to gain electrons.
• Atoms just shy of a full shell display higher affinities.

Understanding electron affinity helps predict reactivity and ion formation tendencies.