Question

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

Short answer

(a) Calcium is generally more reactive than magnesium because it has a lower second ionization energy, attributed to its larger atomic size and higher electron shielding effect, making it easier for calcium to lose electrons. (b) Calcium is generally less reactive than potassium because potassium has a lower first ionization energy, which results from its lower nuclear charge and larger atomic size, allowing potassium to lose an electron more easily and be more reactive than calcium.

Step-by-step solution

Part (a): Electron configurations

First, let's look at the electron configurations and the periodic table positions of calcium (Ca) and magnesium (Mg). Calcium (Ca): Atomic number 20, Electron configuration: [Ar] 4s² Magnesium (Mg): Atomic number 12, Electron configuration: [Ne] 3s² Both calcium and magnesium belong to the same group (Group 2) in the periodic table, making them alkaline earth metals.

Part (a): Ionization energy

In order to compare reactivity, we can look at the ionization energy, which represents the energy needed to remove an electron from an atom. The lower the ionization energy, the more easily an element loses an electron, and the more reactive it is. Group 2 elements typically lose 2 electrons to form a ²⁺ ion, so we will compare the second ionization energies of calcium and magnesium.

Part (a): Trends in the periodic table

As we move down a group in the periodic table, ionization energies generally decrease due to: 1. An increase in atomic size 2. Electron shielding effect Calcium has a lower second ionization energy than magnesium because it has a larger atomic size and higher electron shielding effect, which makes it easier for calcium to lose electrons and be more reactive than magnesium.

Part (b): Electron configurations

Now, let's compare the reactivity of calcium (Ca) and potassium (K). Potassium (K): Atomic number 19, Electron configuration: [Ar] 4s¹ Note that potassium is in the same period as calcium but belongs to a different group (Group 1) in the periodic table, making it an alkali metal.

Part (b): Ionization energy

Alkali metals typically lose 1 electron to form a ¹⁺ ion, so we will compare the first ionization energies of calcium and potassium.

Part (b): Trends in the periodic table

As we move from left to right in a period in the periodic table, ionization energies generally increase due to: 1. An increase in nuclear charge 2. A decrease in atomic size Potassium has a lower first ionization energy than calcium because it has a lower nuclear charge and larger atomic size, making it easier for potassium to lose an electron and be more reactive than calcium.