Group 16 elements: The Oxygen Family

The modern periodic table’s group 16 elements are composed of five elements: oxygen, sulphur, selenium, tellurium, and polonium. Because many elements can be extracted from sulphide or oxide ores, the elements in this group are also known as chalcogens or ore-forming elements. Oxygen is abundant on the planet. When the proportions of different types of atoms found in the universe were calculated, oxygen was determined to be the fourth most abundant element after hydrogen, helium, and neon. It constitutes about 89% of water, 46% of the earth crust and 20 % of the air.

Element	Symbol	Atomic Number	Electronic Configuration
Oxygen	O	8	[He] 2s2 2p4
Sulphur	S	16	[Ne] 3s2 3p4
Selenium	Se	34	[Ar] 3d10 4s2 4p4
Tellurium	Te	52	[Kr] 4d10 5s2 5p4
Polonium	Po	84	[Xe]4f14 5d10 6s2 6p4

Oxygen

Oxygen is denoted by the chemical symbol O. It is a colourless and odourless gas that is converted into carbon dioxide during the human respiration process. Oxygen is a diatomic molecule. Oxygen is also found in trace amounts as a triatomic molecule (O₃), which is known as ozone. Many elements combine easily with oxygen. The evolution of heat energy occurs during the combination with some elements; this process is known as combustion.

Sulphur

The symbol S represents sulphur. It’s a nonmetal that ranks ninth in terms of cosmic abundance. Sulphur can be found in both the combined and free states. Sulphates account for about 0.09 percent of the sulphur found in seawater. The meteorite contains 12% sulphur, and a significant amount of sulphur is found in underground deposits of pure sulphur present in dome-like structures. Sulphur is formed in this environment by the action of anaerobic bacteria on sulphate minerals such as gypsum.

Selenium

Selenium is rarer than oxygen or sulphur. It can be found in a few minerals both free and combined with heavy metals (such as lead, silver, or mercury). Under typical settings, the grey metallic form of selenium is the most stable form of the element.

Tellurium

Tellurium is a chemical element with the atomic number 52 and properties intermediate between metals and nonmetals. It is one of the earth’s crust’s rarest stable elements. It is frequently found in its free state as well as in compounds with elements such as copper, lead, silver, and gold.

Polonium

It is the rarest element in the group of sixteen elements. It is a radioactive substance. Polonium is occasionally used in alpha radiation applications in science.

Physical Properties of the Chalcogens

Atomic/Ionic Radii

Elements’ atomic radii or ionic radii increase as they progress down a group. The chalcogen with the smallest atomic and ionic radius is oxygen, while the chalcogen with the largest (excluding livermorium) is polonium. The addition of protons and the increase in the effective nuclear charge cause the atomic radii of elements to decrease over time. As a result, oxygen’s atomic radius will be much smaller than lithium’s.

Ionization Enthalpies

The atomic radii or ionic radii of elements increase as they move down the periodic table. The chalcogen with the smallest atomic and ionic radius (excluding livermorium) is oxygen, and the chalcogen with the largest (excluding livermorium) is polonium. The addition of protons and the increase in effective nuclear charge cause elements’ atomic radii to decrease over time. As a result, the atomic radius of oxygen will be much smaller than that of lithium.

Electron Gain Enthalpies

It decreases with an increase in the atom’s size. As a result, the electron gain enthalpies of the chalcogens decrease as one moves down the group. It is worth noting that oxygen has a lower negative electron gain enthalpy than sulphur, which can be attributed to the compressed atomic structure of oxygen, which contributes to interelectronic repulsion between the valence electrons and any other approaching electron.

Electronegativities

The electronegativity decreases as one moves down a group due to a variety of factors, including an increase in atomic radius and an increase in electron-electron repulsion. The most electronegative chalcogen is oxygen, and the least electronegative chalcogen is polonium (livermorium not considered).

Metallic Nature

Non-metal elements include oxygen and sulphur. Metalloids include selenium and tellurium. Under normal conditions, polonium has metallic properties. It should be noted, however, that polonium is a radioactive element. 

Melting and Boiling Points

The melting and boiling points of elements increase as they progress down a group due to the increase in atomic sizes and atomic masses (as a result of increased intermolecular forces of attraction). Among chalcogens, oxygen has the lowest melting and boiling points. The significant difference in the melting and boiling points of sulphur and oxygen can be attributed to the fact that oxygen exists in the atmosphere as a diatomic molecule, whereas sulphur is typically found as a polyatomic molecule.

Chemical Properties of the Chalcogens

Allotropes

Almost all chalcogens have multiple allotropes. The most common oxygen allotropes are dioxygen and ozone. In fact, there are nine known allotropes of oxygen. Furthermore, there are over 20 known allotropes of sulphur. Selenium is known to have at least five different allotropes, while polonium is known to have two. Monoclinic sulphur and rhombic sulphur are the two most stable allotropic forms of sulphur. It should be noted that selenium and tellurium are both crystalline and amorphous elements.

Oxidation States

Because the chalcogens’ general electronic configuration is ns² np⁴, they can achieve a stable electronic configuration by gaining two electrons or participating in covalent bonding. When they gain two electrons, the ion formed has the general formula M₂^– (where M denotes a chalcogen). The chalcogens exhibit regular oxidation states of -2, +2, +4, and +6.

Reactions with Hydrogen

When chalcogens react with dihydrogen, they usually form hydrides with the general formula H₂M (where M can be any chalcogen – oxygen, sulphur, selenium, tellurium, or polonium). This chemical reaction takes the following general form:

M (chalcogen) + H₂ (dihydrogen) → H₂M (hydride of the chalcogen)

Sample Problems

Problem 1: What are the five group 16 elements?

Solution:

Five elements make up the group 16 elements of the current periodic table: oxygen, sulphur, selenium, tellurium, and polonium.

Problem 2: What is the metallic nature of chalcogens?

Solution:

Non-metal elements include oxygen and sulphur. Metalloids are elements like selenium and tellurium. Under normal circumstances, polonium has metallic properties. It’s worth noting, though, that polonium is a radioactive element.

Problem 3: What happens to ionization energy of chalcogens as we move down the group?

Solution:

The ionisation enthalpy reduces as the atom’s size or radius increases (it is easier to remove an electron from an atom with a large atomic radius since the distance between the nucleus and the valence shell will be relatively large). As a result, as the group progresses, the chalcogens’ ionisation enthalpies drop.

Problem 4: What happens to electronegativity of chalcogens as we move down the group?

Solution:

Many reasons, such as the rise in atomic radius and the increase in electron-electron repulsion, cause the electronegativity to drop as one moves down a group. Oxygen is the most electronegative chalcogen, while polonium is the least electronegative (livermorium not considered).

Problem 5: Is polonium a radioactive element? What is it used for?

Solution:

Among the group 16 elements, it is the rarest. It’s a radioactive substance. For alpha radiation, polonium is employed in scientific applications.