Chalcogens on the Periodic Table

Core Concepts

In this article, you will learn about the chalcogens family on the periodic table, as well as their unique characteristics.

Topics Covered in Other Articles

• Electron Orbitals & Orbital Shapes
• Valence Bond Theory
• Entropy
• Ionization Energy
• Atomic Radius Trends

Chalcogens on the Periodic Table

Chalcogens are elements that belong to Group 16 on the periodic table. There are five elements that can be classified as chalcogens: oxygen, sulfur, selenium, tellurium, and polonium. However, the members of this family portrait are subject to debate. Sometimes oxygen is excluded because its characteristics differ a bit from those of the chalcogens, and some scientists consider livormorium to be a member of the chalcogens.

Each element in the chalcogen family has six electrons in its valence shell. These elements derived their name from the Greek word “chalcos,” which means “ore-forming,” since each of these elements are found in copper ores and in sulfides and oxides in the earth’s crust. Most chalcogens have more than one allotrope, the existence of a chemical element in two or more forms. For example, sulfur has over 20 allotropes, and oxygen is known to have about nine.

Electron Configuration for Chalcogens

Generally, the electron configuration for chalcogens is ns²np⁴. The electron configuration for livermorium, which is not displayed in the chart, is [Rn]5f¹⁴6d¹⁰7s²7p⁴.

Chalcogen	Electron Configuration
Polonium (Po)	[Xe]4f145d106s26p4
Sulfur (S)	[Ne]3s23p4
Selenium (Se)	[Ar]3d104s24p4
Tellurium (Te)	[Kr]4d105s25p4
Oxygen (O)	[He]2s22p4

Atomic Radius and Ionic Radius

Both the atomic and ionic radii of the chalcogens are smaller than those of the group immediately preceding them, Group 15. This is because of the increased effective nuclear charge. The greater attraction of the electrons to the nucleus of the atom decrease radius size. As expected based on atomic and ionic radius trends on the periodic table, the radii of the chalcogens increase when we move down a group. So, the chalcogen with the smallest atomic radius and ionic radii is oxygen, while the chalcogen with the largest atomic and ionic radii is polonium.

Melting Points and Boiling Points

Since there is an increase in atomic size and masses when we move down a group on the periodic table, the melting and boiling points of the chalcogens have a direct correlation. As we move down a group, the magnitude of van der Waals forces also increases. Oxygen is known to have the lowest melting and boiling point.

Ionization Energies

When the radius or size of an atom increases, the ionization energy decreases. This is because the greater the distance the electrons in the valence shell are from the nucleus, the less force of attraction the nucleus has on these electrons. Therefore, elements smaller in size will often have higher ionization energies than elements with larger size. Because of this, the ionization energies of the chalcogens decrease as we move down in the group. Oxygen has the highest ionization energy within the Group 16 elements. Also note that, as we move across a period on the periodic table, ionization energy increases. Thus, oxygen has a higher ionization energy than an element like lithium.

Chalcogen Reactions

When the chalcogens react with dihydrogen (H₂), they will usually form hydrides with the formula H₂X. Here, “X” denotes any of the chalcogens: oxygen, sulfur, selenium, tellurium, or polonium.

X (chalcogen) + H₂ (dihydrogen) → H₂X (hydride of the chalcogen)

Characteristics of Chalcogens

Oxygen

• Oxygen’s electron configuration is [He]2s²2p⁴.
• Oxygen forms rust through oxidation, and is known to react with other atoms.
• Oxygen is the least dense of all of the chalcogens, with a density of 0.00143 g/cm³.
• At room temperature, oxygen is in a gaseous state and it is colorless, odorless, and tasteless.
• It reaches its boiling point around -183°C (-297°F).

Polonium

• Polonium is the largest of all the chalcogens.
• Polonium’s electron configuration is [Xe]6s²p⁴.
• Polonium has the highest density, with a density of 9.196 g/cm³.
• Polonium is an exception to the rule of boiling point increasing with atomic weight, as its boiling point is lower than that of tellurium, at 962°C (1,764°F).
• 33 different isotopes of this element can be found on Earth.

Tellurium

• Tellurium’s electron configuration is [Kr]4d¹⁰5s²5p⁴.
• Tellurium has the highest boiling point out of all of the chalcogens, at 988°C (1,810°F).
• It is naturally found as a silver mettaloid when it is in its crystalline form.

Selenium

• Selenium’s electron configuration is [Ar]3d¹⁰4s²4p⁴.
• Although selenium is a non-metal, it can conduct electricity.
• Selenium’s boiling point is also very high at 685°C (1265°F).
• It is naturally found as a reddish powder, but when it is processed, it turns black.
• Selenium is photo-conductive, making it electrically charged when it is exposed to light.

Sulfur

• Sulfur’s electron configuration is [Ne]3s²3p⁴.
• Sulfur has a large range of oxidation states, ranging from -2 to +6.
• This element is found in trace amounts in the earth’s crust and the human body.
• Sulfur is a yellow solid, and produces a rotten smell when it gets burned.