Question

Arrange the following in order of increasing first ionization energy: F, K. P, Ca, and Ne

Short answer

K < Ca < P < F < Ne.

Step-by-step solution

Understand Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in the gaseous state. Generally, ionization energy increases across a period from left to right and decreases down a group in the periodic table.

Identify the Periodic Table Trends

Neon (Ne) is a noble gas and has high ionization energy because its outer shell is full, requiring more energy to remove an electron. Fluorine (F) is in the same period but before neon, so it has slightly less ionization energy than Ne. Phosphorus (P) is further left in the same period, so its ionization energy is less than F. Potassium (K) is in a lower period and is an alkali metal, so it has the lowest ionization energy among these elements.

Compare Ionization Energies

Using the trends, the expected order of increasing ionization energy should be from Potassium (K) having the lowest, then Calcium (Ca), followed by Phosphorus (P), Fluorine (F), and Neon (Ne) with the highest ionization energy. This is consistent with the fact that alkali metals have the lowest ionization energies and noble gases have the highest.

Key concepts

Periodic Table Trends

The periodic table is a powerful tool that helps us understand the chemical properties of elements, including ionization energy. Ionization energy is the energy needed to remove an electron from an atom in its gaseous state. Across a period from left to right, ionization energy generally increases. This happens because the number of protons (or positive charge) increases, pulling the electrons tighter to the nucleus. Thus, more energy is needed to remove an electron. As we move down a group, ionization energy tends to decrease. Even though there are more protons, the addition of energy levels makes the outer electrons further from the nucleus, making them easier to remove.

Noble Gases

Noble gases are a special group of elements located in Group 18 of the periodic table. They include helium (He), neon (Ne), argon (Ar), and others. What sets these elements apart is their full electron shell configuration, which gives them exceptional stability and very low reactivity compared to other elements. Because their outermost shell is complete, noble gases have high ionization energies. This means it takes a lot of energy to remove an electron from a noble gas, as these electrons are tightly held in place. For example, neon has a much higher ionization energy compared to other elements in the same period, causing it to resist losing electrons.

Alkali Metals

Alkali metals are found in Group 1 of the periodic table and include elements like lithium (Li), sodium (Na), and potassium (K). These metals are characterized by having a single electron in their outermost shell. This makes them very reactive, as losing one electron gives them a stable noble gas configuration. Because the electron is relatively far from the nucleus, alkali metals have low ionization energies. This low ionization energy explains why alkali metals are so reactive; they easily lose their one valence electron to form positive ions.

Electron Configuration

Electron configuration helps us understand where the electrons are located around an atom's nucleus. It follows the arrangement of electron shells characterized by specific energy levels or subshells, such as s, p, d, and f. The electron configuration directly influences an element's chemical behavior, including its ionization energy. Elements with a full outer shell, like noble gases, have minimal tendency to lose or gain electrons, leading to higher ionization energies. In contrast, elements with one or few electrons in their outermost shell, such as alkali metals, have lower ionization energies, making them eager to lose electrons and react with other elements.