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Chapter 7: Problem 71

(a) Why is calcium generally more reactive than magnesium? (b) Why is calcium generally less reactive than potassium?

Short Answer

Expert verified
(a) Calcium is generally more reactive than magnesium because it is located below magnesium in Group 2 of the periodic table. This means that calcium's outer electron shell is further from the nucleus, making it easier for calcium to lose its valence electrons compared to magnesium. (b) Calcium is generally less reactive than potassium because potassium is in Group 1, with only one valence electron, making it inherently more reactive than calcium which has two valence electrons. Additionally, the tendency of potassium to lose its valence electron is stronger due to its position in Group 1, despite the shorter distance between its nucleus and the outer electron shell.

Step by step solution

01

(Understand the periodic table)

(First of all, let's locate calcium (Ca), magnesium (Mg), and potassium (K) in the periodic table. Calcium and magnesium are both in Group 2, known as the alkaline earth metals, and potassium is in Group 1, known as the alkali metals. Calcium is located below magnesium in the same group, and potassium is located to the left of calcium in a different group. In general, elements in Group 1 are more reactive than those in Group 2, and reactivity increases as you move down a group. This is because elements in Group 1 have one valence electron, whereas elements in Group 2 have two. Additionally, as you move down a group, the outer electron shell is further from the nucleus, making it easier to lose the valence electrons in chemical reactions.)
02

(Analyze the electron configurations)

(Let's examine the electron configurations of calcium, magnesium, and potassium to better understand their reactivity: Calcium (Ca): \([Ar] 4s^2\) Magnesium (Mg): \([Ne] 3s^2\) Potassium (K): \([Ar] 4s^1\) The reactivity of these elements is determined by the ease with which they can lose their valence electrons to form positive ions.)
03

(a) Explain reactivity difference between calcium and magnesium)

(As mentioned earlier, both calcium and magnesium are in Group 2 and have two valence electrons. Since calcium is located below magnesium in the periodic table, its outer electron shell is further from the nucleus, and the attraction between these valence electrons and the nucleus is weaker. As a result, calcium can lose its valence electrons more easily than magnesium, making it more reactive.)
04

(b) Explain reactivity difference between calcium and potassium)

(On the other hand, potassium is in Group 1 and has only one valence electron. This makes it inherently more reactive than calcium with its two valence electrons. Furthermore, potassium is also located above calcium in the periodic table, and its outer electron shell is closer to the nucleus. However, due to being in Group 1, the tendency of potassium to lose its valence electron is stronger than that of calcium, even with the shorter distance between the nucleus and the outer electron shell. So, potassium is generally more reactive than calcium.)

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Most popular questions from this chapter

The first ionization energy of the oxygen molecule is the energy required for the following process: $$ \mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{2}^{+}(g)+\mathrm{e}^{-} $$ The energy needed for this process is \(1175 \mathrm{~kJ} / \mathrm{mol}\), very similar to the first ionization energy of Xe. Would you expect \(\mathrm{O}_{2}\) to react with \(\mathrm{F}_{2}\) ? If so, suggest a product or products of this reaction.

In the chemical process called electron transfer, an electron is transferred from one atom or molecule to another. (We will talk about electron transfer extensively in Chapter 20.) A simple electron transfer reaction is $$ \mathrm{A}(g)+\mathrm{A}(g) \longrightarrow \mathrm{A}^{+}(g)+\mathrm{A}^{-}(g) $$ In terms of the ionization energy and electron affinity of atom A, what is the energy change for this reaction? For a representative nonmetal such as chlorine, is this process exothermic? For a representative metal such as sodium, is this process exothermic? [Sections 7.4 and 7.5\(]\)

Mercury in the environment can exist in oxidation states 0,+1 , and \(+2 .\) One major question in environmental chemistry research is how to best measure the oxidation state of mercury in natural systems; this is made more complicated by the fact that mercury can be reduced or oxidized on surfaces differently than it would be if it were free in solution. XPS, X-ray photoelectron spectroscopy, is a technique related to PES (see Exercise 7.107 ), but instead of using ultraviolet light to eject valence electrons, X-rays are used to eject core electrons. The energies of the core electrons are different for different oxidation states of the element. In one set of experiments, researchers examined mercury contamination of minerals in water. They measured the XPS signals that corresponded to electrons ejected from mercury's 4 forbitals at \(105 \mathrm{eV},\) from an X-ray source that provided \(1253.6 \mathrm{eV}\) of energy. The oxygen on the mineral surface gave emitted electron energies at \(531 \mathrm{eV}\), corresponding to the 1 s orbital of oxygen. Overall the researchers concluded that oxidation states were +2 for \(\mathrm{Hg}\) and -2 for \(\mathrm{O} .\) (a) Calculate the wavelength of the X-rays used in this experiment. (b) Compare the energies of the \(4 f\) electrons in mercury and the 1 s electrons in oxygen from these data to the first ionization energies of mercury and oxygen from the data in this chapter. (c) Write out the ground- state electron configurations for \(\mathrm{Hg}^{2+}\) and \(\mathrm{O}^{2-}\); which electrons are the valence electrons in each case? (d) Use Slater's rules to estimate \(Z_{\text {eff }}\) for the \(4 f\) and valence electrons of \(\mathrm{Hg}^{2+}\) and \(\mathrm{O}^{2-}\); assume for this purpose that all the inner electrons with \((n-3)\) or less screen a full + \(1 .\)

Compare the elements bromine and chlorine with respect to the following properties: (a) electron configuration, (b) most common ionic charge, (c) first ionization energy, (d) reactivity toward water, (e) electron affinity, (f) atomic radius. Account for the differences between the two elements.

Identify each statement as true or false. If it is false, rewrite it so that it is true: (a) Ionization energies are always negative quantitites. (b) Oxygen has a larger first ionization energy than fluorine. (c) The second ionization energy of an atom is always greater than its first ionization energy.
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