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Chapter 7: Problem 63

(a) Explain why the sizes of atoms change when proceeding across a period of the periodic table. (b) Explain why the sizes of transition metal atoms change very little across a period.

Short Answer

Expert verified
(a) Atomic size decreases across a period due to increased nuclear charge pulling electrons closer; (b) Transition metals have little change in size due to inner d electron shielding.

Step by step solution

01

Understanding Atomic Size Across a Period

When moving across a period (from left to right) on the periodic table, atomic size generally decreases. This is due to an increase in the number of protons and electrons, with the additional electrons being added to the same energy level, or shell. The increase in positive charge on the nucleus pulls the electron cloud closer to the nucleus, thereby decreasing the atomic radius.
02

Considering Electron Configuration

As you move across a period, more electrons are added to the same outer shell without adding new energy levels. The effective nuclear charge (the pull exerted on a single electron by the nucleus) increases, causing the electrons to be drawn closer to the nucleus, reducing atomic size.
03

Analysis of Transition Metals' Atomic Size

In transition metals, electrons are added to the inner d subshell instead of the outer shell. As a result, these added electrons experience significant shielding effect, which counteracts the increased nuclear charge. This leads to a relatively constant atomic size across a period of transition metals because the outer s electrons' energy levels remain essentially unaltered.
04

Effective Nuclear Charge in Transition Metals

For transition metals, the increase in nuclear charge is partially offset by the shielding effect of d electrons, which are less effective at screening than s or p electrons. Consequently, the outer electron cloud is not pulled significantly closer to the nucleus as additional protons are added across the period, leading to little change in atomic size.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Periodic Table
The periodic table is a systematic arrangement of elements where the atomic number of each element increases from left to right across a period and from top to bottom across a group. It helps us understand atomic size trends by displaying how elements with similar properties group together. As you move across a period, elements gain more protons and electrons. These additional electrons fill the same energy level, causing an increased nuclear charge that pulls electrons closer to the nucleus.

However, moving down a group in the periodic table, additional electron shells are added, increasing the atomic size. The element's vertical position in a group is linked with its outer electron shell, with more shells leading to a larger atomic radius. By organizing elements in this way, the periodic table provides a powerful tool for predicting and explaining the chemical behavior of the elements.
Effective Nuclear Charge
Effective nuclear charge refers to the net positive charge experienced by electrons in an atom. It is an essential concept for understanding atomic size across a period. This charge is not equal to the actual nuclear charge due to the shielding effects of inner-shell electrons that block some of the nucleus's positive charge.

As you move from left to right in a period, more protons are added to the nucleus, increasing the nuclear charge. Simultaneously, more electrons are added to the outer shell without introducing additional shielding layers because they occupy the same energy level. Thus, the effective nuclear charge felt by outer electrons increases.
  • This increased pull draws the electron cloud closer, reducing atomic size as electrons are attracted more strongly toward the nucleus.
  • Understanding effective nuclear charge helps in explaining why atoms shrink in size as one moves across a period, contributing to the effectiveness of the periodic table in showcasing element trends.
Transition Metals
Transition metals are a unique group of elements found in the center of the periodic table. They occupy the d-block, and their atomic size shows distinctive trends compared to s- and p-block elements. When moving across a period within transition metals, electrons are added to an inner d subshell, which alters their behavior with respect to atomic size.

The d electrons provide a shielding effect that differs from s and p electrons, affecting the effective nuclear charge experienced by the outer s electrons. Despite additional protons increasing the nuclear charge, the poor screening by the d electrons prevents a substantial change in atomic size.
  • This distinct electron configuration means that transition metals experience little change in atomic size across periods.
  • The d electrons have a stabilizing effect, making these metals useful in forming complex ions and catalytic processes because of their ability to accommodate various oxidation states.
  • Understanding the properties of transition metals helps in applications ranging from industrial catalysts to the development of new materials.

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Most popular questions from this chapter

Answer each of the following questions: (a) Of the elements \(\mathrm{S}\), Se, and Cl, which has the largest atomic radius? (b) Which has the larger radius, Br or Br'? (c) Which should have the largest difference between the first and second ionization energy: Si, Na, P, or Mg? (d) Which has the largest ionization energy: \(\mathrm{N}, \mathrm{P}\), or \(\mathrm{As}\) ? (e) Which of the following has the largest radius: \(\mathbf{O}^{2-}\) \(\mathrm{N}^{3-},\) or \(\mathrm{F}^{-} ?\)

Compare the elements \(\mathrm{B}, \mathrm{Al}, \mathrm{C},\) and \(\mathrm{Si}\) (a) Which has the most metallic character? (b) Which has the largest atomic radius? (c) Which has the most negative electron attachment enthalpy? (d) Place the three elements \(\mathrm{B}, \mathrm{Al}\), and \(\mathrm{C}\) in order of increasing first ionization energy.

One compound found in alkaline batteries is \(\mathrm{NiOOH},\) a compound containing \(\mathrm{Ni}^{3+}\) ions. When the battery is discharged, the \(\mathrm{Ni}^{3+}\) is reduced to \(\mathrm{Ni}^{2+}\) ions las in \(\left.\mathrm{Ni}(\mathrm{OH})_{2}\right] .\) Using orbital box diagrams and the noble gas notation, show electron configurations of these ions. Ts either of these ions paramagnetic?

Write the electron configurations for \(\mathrm{Mg}\) and Ar using both spdf notation and orbital box diagrams. Describe the relationship of the atom's electron configuration to its position in the periodic table.

Manganese is found as \(\mathrm{MnO}_{2}\) in deep ocean deposits. (a) Depict the electron configuration of this element using the noble gas notation and an orbital box diagram. (b) Using an orbital box diagram, show the electrons beyond those of the preceding noble gas for the \(4+\) ion. (c) Is the \(4+\) ion paramagnetic? (d) How many unpaired electrons does the Mn \(^{4+}\) ion have?
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