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Chapter 7: Problem 67

(a) Why is calcium generally more reactive than beryllium? (b) Why is calcium generally less reactive than rubidium?

Short Answer

Expert verified
(a) Calcium is more reactive than beryllium because it has a larger atomic radius (1.97 Å) and a lower ionization energy (590 kJ/mol), making it easier for calcium to lose electrons. (b) Calcium is less reactive than rubidium because rubidium has a larger atomic radius (2.50 Å) and a lower ionization energy (403 kJ/mol), allowing rubidium to lose electrons more easily.

Step by step solution

01

a) Comparing Reactivity of Calcium and Beryllium

Calcium (Ca) belongs to Group 2 (alkaline earth metals) and Period 4, while Beryllium (Be) also belongs to Group 2 and Period 2. As we go down a group in the periodic table, the atomic radius increases due to the addition of electron shells. Calcium has an atomic radius of 1.97 Å, while beryllium has a smaller atomic radius of 1.11 Å. A larger atomic radius means that the valence electrons are farther away from the nucleus, making it easier for them to be lost. This makes calcium more reactive than beryllium. In addition, ionization energy (the energy required to remove an electron) decreases as we go down a group in the periodic table. Calcium has a lower ionization energy (590 kJ/mol) than beryllium (899 kJ/mol), so calcium will lose electrons more easily. This is another reason why calcium is more reactive than beryllium.
02

b) Comparing Reactivity of Calcium and Rubidium

Calcium and Rubidium (Rb) both belong to Period 4 in the periodic table, but rubidium is in Group 1 (alkali metals), while calcium is in Group 2. As we move from left to right within a period, the atomic radius decreases, and ionization energy generally increases. Rubidium has an atomic radius of 2.50 Å and an ionization energy of 403 kJ/mol, while calcium has an atomic radius of 1.97 Å and an ionization energy of 590 kJ/mol. Rubidium's larger atomic radius and lower ionization energy mean that it loses electrons more easily than calcium. Since reactivity of metals is related to their ability to lose electrons easily, rubidium is more reactive than calcium.

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Most popular questions from this chapter

(a) The five most abundant elements in the Earth's crust are $\mathrm{O}, \mathrm{Si}, \mathrm{Al}, \mathrm{Fe},\( and Ca. Referring to Figure \)7.1,$ are any of these elements among those known before \(1700 ?\) If so which ones? (b) Seven of the nine elements known since ancient times are metals. Referring to Table \(4.5,\) are these metals mostly found at the bottom or top of the activity series?

Consider the isoelectronic ions \(\mathrm{Cl}^{-}\) and \(\mathrm{K}^{+}\). (a) Which ion is smaller? (b) Using Equation 7.1 and assuming that core electrons contribute 1.00 and valence electrons contribute nothing to the screening constant, \(S,\) calculate \(Z_{\text {eff }}\) for these two ions. (c) Repeat this calculation using Slater's rules to estimate the screening constant, $S .(\mathbf{d})$ For isoelectronic ions, how are effective nuclear charge and ionic radius related?

Based on their positions in the periodic table, predict which atom of the following pairs will have the smaller first ionization energy: (a) $\mathrm{Br}, \mathrm{Kr} ; \mathbf{( b )} \mathrm{C}, \mathrm{Ca} ;(\mathbf{c}) \mathrm{Li}, \mathrm{Rb} ;\(; (d) \)\mathrm{Pb}, \mathrm{Si} ;$ (e) \(\mathrm{Al}, \mathrm{B}\).

Detailed calculations show that the value of \(Z_{\text {eff }}\) for the outermost electrons in \(\mathrm{Si}\) and \(\mathrm{Cl}\) atoms is \(4.29+\) and \(6.12+,\) respectively. (a) What value do you estimate for \(Z_{\text {eff }}\) experienced by the outermost electron in both Si and Cl by assuming core electrons contribute 1.00 and valence electrons contribute 0.00 to the screening constant? (b) What values do you estimate for \(Z_{\text {eff }}\) using Slater's rules? (c) Which approach gives a more accurate estimate of \(Z_{\text {eff }} ?\) (d) Which method of approximation more accurately accounts for the steady increase in \(Z_{\text {eff }}\) that occurs upon moving left to right across a period? (e) Predict \(Z_{\text {eff }}\) for a valence electron in P, phosphorus, based on the calculations for \(\mathrm{Si}\) and \(\mathrm{Cl}\).

Moseley's experiments on \(\mathrm{X}\) rays emitted from atoms led to the concept of atomic numbers. (a) If arranged in order of increasing atomic mass, which element would come after chlorine? (b) Describe two ways in which the properties of this element differ from the other elements in group $8 \mathrm{~A}$.
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