The elements oxygen, sulphur, selenium, tellurium and polonium constitute group 16 elements of the periodic table. These are named as oxygen group elements after the name of the first member of the group. The oxygen group number is 16. The first four elements (oxygen, sulphur, selenium, and tellurium) of the 16th group are known as chalcogens. This is because many naturally occurring metal ores occur as oxides and sulphides. Group 16 elements are called chalcogens.
The components having a place in Group 16 of the occasional table are portrayed by electron setups in which six electrons possess the peripheral shell. An atom having such an electronic design will in general, frame a steady shell of eight electrons by adding two more charges. This propensity to frame adversely charged particles, ordinary of nonmetallic components, is quantitatively communicated in the properties of electronegativity (the supposition of halfway bad charge when present in the covalent blend) and electron proclivity (the capacity of a nonpartisan molecule to take up an electron, shaping a negative particle).
Both these properties decline in force as the components expand in nuclear number and mass procedure down section 16 of the intermittent table. Oxygen has, with the exception of fluorine, the most elevated electronegativity and electron partiality of any component; the upsides of these properties then, at that point, decline strongly for the excess individuals from the gathering to the degree that tellurium and polonium are viewed as prevalently metallic in nature, having a tendency to lose instead of acquiring electrons in compound development.
Group 16 Elements
Oxygen is the most abundant of all elements. It occurs in the free form as an oxygen molecule and makes up 20.946% of the volume of the atmosphere. Most of it has been produced by photosynthesis. Oxygen makes up the major component of the earth crust. It occurs in the silicates mineral. It also occurs as metal oxide ores and deposits of oxo salts such as carbonates, sulphates, nitrates, and borates. As water, it comprises 89% by weight of the oceans. Oxygen occurs as ozone, an allotrope of oxygen in the upper atmosphere and is of great importance.
Sulphur- Sulphur is the non-metallic element and it is the sixteenth most abundant element found on the earth crust. It constitutes 0.03 - 0.1% by the mass of the earth’s crust. It occurs in the combined form of sulphides ores and sulphate ores. The other elements are comparatively rare.
Selenium and tellurium are more electronegative than metals. Therefore, they occur as metal selenides and tellurides in the naturally occurring sulphide ores. Selenium and tellurium are found in anode mud or the anode slime deposited during the electrolytic refining of copper.
General Characteristics of the Oxygen Group Elements
Similar to the case inside all gatherings of the table, the lightest component—the one of the littlest nuclear numbers—has outrageous or overstated properties. Oxygen, on account of the little size of its molecule, the modest number of electrons in its hidden shell, and the enormous number of protons in the core comparative with the nuclear range, has properties interestingly unique in relation to those of sulfur and the excess chalcogens. Those components act in an actually unsurprising and intermittent manner.
Albeit even polonium displays the oxidation state −2 in shaping a couple of parallel mixtures of the kind MPO (in which M is a metal), the heavier chalcogens don't frame the negative state promptly, leaning toward positive states, for example, +2 and +4. Every one of the components in the gathering aside from oxygen might accept positive oxidation states, with the even qualities prevailing, yet the most noteworthy worth, +6, is certainly not a truly steady one for the heaviest individuals. At the point when this state is accomplished, there is a solid main thrust for the atom to get back to a lower state, frequently to the basic structure. This inclination makes compounds containing Se (VI) and Te (VI) more remarkable oxidizing specialists than S (VI) compounds. On the other hand, sulfides, selenides, and tellurides, in which the oxidation state is −2, are solid lessening specialists, effectively oxidized to the free components.
Neither sulfur nor selenium, and unquestionably not oxygen, frames absolutely ionic bonds to a nonmetal particle. Tellurium and polonium structure a couple of mixtures that are fairly ionic; tellurium (IV) sulfate, Te (SO4)2, and polonium (II) sulfate, PoSO4, are models.
1. Electronic Configuration
The elements of the oxygen family have six electrons in the outermost shell and have the general electronic configuration s ns2 np4. The electronic configurations of the oxygen family are given below:
2. Atomic and Ionic Radii
The atomic and ionic radii of the elements of the oxygen periodic table group is smaller than that of the corresponding elements of group 15. The atomic radii and ionic radii of the group 16th elements is expected to increase on moving down the group. The comparatively smaller atomic and ionic radii of the oxygen group elements compared to group 15 elements are due to the increased effective nuclear charge of group 16 elements. Due to this, there is a greater attraction of the electrons by the nucleus and hence radii are less. The increase in the atomic radii of the 16th group elements, moving down the group is due to the increment in the number of electron shells.
3. Ionization Enthalpies
The ionization enthalpies of the elements of the oxygen family are less than those of the nitrogen family. On moving down the group from oxygen element to polonium element, the ionization enthalpy or potential decreases.
The general trend of the ionization enthalpy is, it increases when we move from left to right. But when we move from the nitrogen group to the oxygen group the ionization enthalpy decreases. This happens because the nitrogen is completely half-filled p-orbitals. This half-filled configuration is stable because a half-filled and filled configuration has extra stability due to more exchange energy. But the configuration of oxygen is less stable and therefore, has less ionization enthalpy. However, it may be noted that the second ionization enthalpies (IE2) of the members of group 16 are higher than those of group 15. This is because, after the removal of the first electron, the second electron has to be removed from a more symmetrical half-filled configuration, which is more stable.
The elements of the 16th group (chalcogen group) have higher values of electronegativity than the corresponding group 15 elements. The electronegativity decreases on going down the group. The decrease in electronegativity down the group is due to an increase in the size of the atoms.
5. Electron Gain Enthalpy
The oxygen family elements have high negative electron gain enthalpies. The value decreases down the group from sulphur to polonium. Oxygen exceptionally has low negative electron gain enthalpy. This characteristic is attributed to the small size of the oxygen atom so that its electron cloud is distributed over a small region of space and therefore, it repels the incoming electrons.
One more component of the Group 16 components that equals drifts commonly displayed in sections of the occasional table is the expanding security of particles having the piece X (OH)n as the size of the focal molecule, X, increments. There is no compound HO―O―OH, wherein the focal oxygen particle would have a positive oxidation expression, a condition that it stands up to. The practically equivalent sulfur compound HO―S―OH, albeit not known in the unadulterated state, has a couple of stable subordinates as metal salts, the sulphoxylate. All the more profoundly hydroxylated mixtures of sulfur, S(OH)4 and S(OH)6, additionally don't exist, not in view of sulfur's protection from a positive oxidation state but instead due to the high charge thickness of the S(IV) and S(VI) states (the huge number of positive charges comparative with the little measurement of the atom), which repulses the electropositive hydrogen atoms, and the swarming that goes to the covalent holding of six oxygen molecules to sulfur, leaning toward loss of water.
As the size of the chalcogen molecule expands, the soundness of the hydroxylated intensifies builds: the compound orthotellurate corrosive, The (OH)6, is fit for presence.
Did You Know?
Oxygen is the second most electronegative element, the first being fluorine.
Only sulphur is an element in the oxygen group that shows catenation property.
All the group 16 elements exhibit allotropy.