Question

Explain, in terms of ionization energies, why strontium is more reactive than calcium.

Short answer

Strontium is more reactive than Calcium because it has lower ionization energy. This is because Strontium's electrons are further away from its nucleus as compared to Calcium, and can hence be lost more easily, making it more reactive.

Step-by-step solution

Understand the basics

Firstly, understand that reactivity of an element depends on its ability to lose or gain electrons. An element that loses electrons easily is more likely to be reactive. The energy required to remove an electron from an atom in its gaseous state is called ionization energy. Therefore, lower the ionization energy, more easily an element can lose electrons, and hence, more reactive it is.

Look at the periodic table

Strontium (Sr) and Calcium (Ca) are both in the same group (group 2 - alkaline earth metals) in the periodic table. In a group, as we move down, the size of the atoms increases as new energy levels (shells) are added. When the atomic size increases, the outermost electrons are further away from the nucleus and hence, the attraction of the nucleus towards these electrons decreases.

Compare ionization energies

Due to less nuclear attraction, outermost electrons can be removed more easily in Strontium (Sr) than in Calcium (Ca). Thus, ionization energy of Strontium is less than that of Calcium. Strontium can lose electrons more easily than Calcium and is therefore more reactive than Calcium.

Key concepts

Ionization Energy

Ionization energy is a fundamental concept in chemistry that refers to the amount of energy required to remove an electron from an atom in its gaseous state. This process is crucial because it indicates how easily an atom can lose an electron in a chemical reaction. Atoms with lower ionization energies tend to lose electrons more readily, making them more reactive.

For example, in a comparison between strontium and calcium, strontium's lower ionization energy means that it requires less energy to remove its outermost electron compared to calcium. This makes strontium more reactive. Understanding ionization energy is vital for predicting the behavior of elements in different reactions and their placement in the periodic table.

Periodic Table Trends

The periodic table is organized in such a way that we can predict various properties of elements, including their ionization energy. As you progress across a period from left to right, ionization energy generally increases due to increased nuclear charge, which pulls the electrons closer to the nucleus. This makes it harder to remove an electron.

However, when you move down a group, like the alkaline earth metals, the ionization energy typically decreases. This is because the added energy levels mean that the outer electrons are further away from the nucleus and thus experience less attraction. Understanding these trends helps in predicting how elements might interact with each other in chemical reactions.

Alkaline Earth Metals

The alkaline earth metals, which include elements like strontium and calcium, are found in group 2 of the periodic table. These elements are characterized by having two electrons in their outermost shell. This makes them relatively reactive, as they tend to lose these electrons in order to achieve a stable electronic configuration.

Their reactivity increases as you move down the group. This is due to the decrease in ionization energy, meaning that elements like strontium, which are lower on the group, can lose their outer electrons more easily compared to elements higher up, like calcium.

• Elements from this group are typically shiny and somewhat soft metals.
• They easily react with halogens and water, though not as vigorously as alkali metals.
• Much of their chemistry can be explained by their tendency to lose two electrons during reactions.

These characteristics make alkaline earth metals important in numerous industrial and chemical applications.