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Ch.7 - Periodic Properties of the Elements
All textbooksBrown 14th EditionCh.7 - Periodic Properties of the ElementsProblem 103
Chapter 7, Problem 103

Elemental barium reacts more violently with water than does elemental calcium. Which of the following best explains this difference in reactivity? (i) Calcium has greater metallic character than does barium. (ii) The electron affinity of calcium is smaller than that of barium. (iii) The first and second ionization energies of barium are less than those of calcium. (iv) The atomic radius of barium is smaller than that of calcium. (v) The ionic radius of the barium ion is larger than that of the calcium ion.

Verified step by step guidance
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Step 1: Understand the reactivity of alkaline earth metals with water. Alkaline earth metals, such as barium and calcium, react with water to form hydroxides and hydrogen gas. The reactivity increases down the group in the periodic table.
Step 2: Consider the concept of ionization energy. Ionization energy is the energy required to remove an electron from an atom. Lower ionization energy means it is easier for the atom to lose an electron and react.
Step 3: Compare the ionization energies of barium and calcium. Barium, being lower in the group, has lower ionization energies compared to calcium, making it more reactive.
Step 4: Evaluate the atomic radius. Barium has a larger atomic radius than calcium, which means its outer electrons are further from the nucleus and more easily removed, contributing to higher reactivity.
Step 5: Analyze the given options. The correct explanation for the increased reactivity of barium compared to calcium is that the first and second ionization energies of barium are less than those of calcium, making option (iii) the best explanation.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Metallic Character

Metallic character refers to the tendency of an element to lose electrons and form positive ions. It generally increases down a group in the periodic table due to the increasing atomic size and decreasing ionization energy. In this context, understanding the metallic character of calcium and barium helps explain their reactivity with water, as more metallic elements tend to react more vigorously.
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Metallic Character Example

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. Elements with lower ionization energies can lose electrons more easily, leading to higher reactivity. In the case of barium and calcium, comparing their first and second ionization energies is crucial to understanding why barium reacts more violently with water.
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Atomic and Ionic Radius

The atomic radius is the distance from the nucleus to the outermost electron shell, while the ionic radius refers to the size of an ion in a crystal lattice. Generally, as you move down a group in the periodic table, atomic and ionic radii increase. This increase affects the reactivity of elements, as larger ions can lead to different interactions with water, influencing the overall reaction dynamics.
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Related Practice
Textbook Question

The first ionization energy of the oxygen molecule is the energy required for the following process: O21g2¡O2 +1g2 + e- The energy needed for this process is 1175 kJ>mol, very similar to the first ionization energy of Xe. Would you expect O2 to react with F2? If so, suggest a product or products of this reaction.

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Textbook Question

It is possible to define metallic character as we do in this book and base it on the reactivity of the element and the ease with which it loses electrons. Alternatively, one could measure how well electricity is conducted by each of the elements to determine how 'metallic' the elements are. On the basis of conductivity, there is not much of a trend in the periodic table: Silver is the most conductive metal, and manganese the least. Look up the first ionization energies of silver and manganese; which of these two elements would you call more metallic based on the way we define it in this book?

Textbook Question

Which of the following is the expected product of the reaction of K(s) and H2(g)? (i) KH(s), (ii) K2H(s), (iii) KH2(s), (iv) K2H2(s), or (v) K(s) and H2(g) will not react with one another.

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Textbook Question

A historian discovers a nineteenth-century notebook in which some observations, dated 1822, were recorded on a substance thought to be a new element. Here are some of the data recorded in the notebook: 'Ductile, silver-white, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: 153 °C. Density: 7.3 g>cm3. Electrical conductivity: 20% that of copper. Hardness: About 1% as hard as iron. When 4.20 g of the unknown is heated in an excess of oxygen, 5.08 g of a white solid is formed. The solid could be sublimed by heating to over 800 °C.' (a) Using information in the text and the CRC Handbook of Chemistry and Physics, and making allowances for possible variations in numbers from current values, identify the element reported.