Question

Arrange the following atoms in order of increasing first ionization energy: axygen, tellurium, selenium.

Short answer

Tellurium < Selenium < Oxygen

Step-by-step solution

Understand First Ionization Energy

First ionization energy is the energy required to remove the most loosely bound electron from a neutral atom in its ground state. It generally increases across a period from left to right and decreases down a group in the periodic table.

Locate the Elements in the Periodic Table

Locate the position of oxygen (O), selenium (Se), and tellurium (Te) in the periodic table. Oxygen is in the second period; selenium and tellurium are in the same group as oxygen but in the third and fourth periods, respectively.

Compare Positions in the Periodic Table

Since the ionization energy decreases down a group, we know that oxygen will have a higher first ionization energy than selenium and tellurium. Between selenium and tellurium, since selenium is above tellurium in the periodic table, selenium will have a higher first ionization energy than tellurium.

Arrange the Atoms

Now arrange the atoms in order of increasing first ionization energy based on the trends identified. The order is: tellurium < selenium < oxygen.

Key concepts

The Periodic Table and First Ionization Energy

The periodic table is a comprehensive chart that organizes all known elements according to their atomic number and chemical properties. Understanding the layout of the periodic table is pivotal when considering trends like the first ionization energy. As outlined in the exercise, first ionization energy tends to increase as one moves from left to right across a period. This is due to the increasing nuclear charge which attracts the electrons more strongly, making them harder to remove.

In contrast, as one moves down a group, first ionization energy decreases. This is because the electrons being removed are further away from the nucleus due to the larger atomic size, and thus feel a reduced effective nuclear charge. Consequently, when asked to arrange elements such as oxygen, selenium, and tellurium by their first ionization energies, one must consider their positions on the periodic table in terms of periods and groups to make accurate comparisons.

Atomic Structure and Ionization Energy

The atomic structure of an element is closely connected to its first ionization energy. Each atom consists of a nucleus, made up of protons and neutrons, surrounded by electrons in defined energy levels, or shells. The most loosely bound electron, typically the one in the outermost shell, is the one involved in the first ionization energy.

For example, in oxygen with atomic number 8, the electron configuration ends with p₄, indicating four electrons in the outer p-orbital. These electrons are relatively closer to the nucleus and experience a strong attraction. For selenium (Se) and tellurium (Te), while they share the same group with oxygen, they have additional inner shells that shield the outer electrons, reducing the nuclear attraction and therefore have lower first ionization energies compared to oxygen. This highlights how atomic structure directly impacts an element's propensity to lose or gain electrons.

Chemical Properties Tied to Ionization Energy

An element's chemical properties are greatly influenced by its first ionization energy. High ionization energy generally signifies that an element is less likely to form cations, which are positively charged ions created when an atom loses an electron. This is typical of nonmetals, which are more apt to gain electrons and form anions. In contrast, elements with low ionization energies, which are easily ionized, are typically metals that readily form cations.

Applying this understanding to our example, oxygen, with its higher ionization energy, is a nonmetal that tends to gain electrons to form anions. Selenium and tellurium, while also nonmetals, have progressively lower ionization energies as one moves down the group, indicating a gradual shift in chemical behavior. This shift can affect their chemical reactivity, the types of bonds they form, and their role in chemical reactions.