8 Oxygen

Discovered in: 1772

Discovered by: Joseph Priestley

Properties:

It's a highly reactive nonmetallic element and a strong oxidizing agent and has the second-highest electronegativity of all reactive elements.

It is an important part of the atmosphere and is necessary to sustain terrestrial life. Because it comprises most of the mass in water, it also comprises most of the mass of living organisms. All major classes of structural molecules in living organisms, such as proteins, carbohydrates, and fats, contain oxygen, as do the major inorganic compounds that comprise animal shells, teeth, and bone.

Elemental oxygen (O₂) is produced by cyanobacteria, algae, and plants through the process of photosynthesis, and is used in cellular respiration by most living organisms on earth. Interstingly, oxygen can be toxic to obligate anaerobic organisms (organisms which need a lack of oxygen for survival), which were the dominant form of early life on Earth, until O₂ began to accumulate in the atmosphere.

16 Sulfur

Discovered in: 1777

Discovered by: Antoine-Laurent de Lavoisier

Properties:

Sulfur burns with a blue flame, concomitant with formation of sulfur dioxide, notable for its peculiar suffocating odor. Sulfur is insoluble in water but soluble in carbon disulfide and, to a lesser extent, in other nonpolar organic solvents, such as benzene and toluene.

The first and the second ionization energies of sulfur are 999.6 and 2252 kJ/mol, respectively. Despite such figures, S²⁺ is rare, with S⁴⁺ and S⁶⁺ being more common. The fourth and sixth ionization energies are 4556 and 8495.8 kJ/mol. The magnitude of the figures is caused by electron transfer between orbitals; these states are only stable with strong oxidants such as fluorine, oxygen, and chlorine.

Sulfur forms stable compounds with all elements except the noble gases. Common oxidation states of sulfur range from −2 to +6. For some organic sulfur compounds, smell depends on their concentration. The sulfur-containing monoterpenoid grapefruit mercaptan has the characteristic scent of grapefruit in small concentrations, but has a unpleasant thiol odor at larger concentrations.

34 Selenium

Discovered in: 1817

Discovered by: Jons Jacob Berzelius

Properties:

It is a fairly reactive element. It combines easily with hydrogen, fluorine, chlorine, and bromine. It reacts with nitric and sulfuric acids. It also combines with a number of metals to form compounds called selenides.

52 Tellurium

Discovered in: 1782

Discovered by: Franz Joseph Müller von Reichenstein

Properties:

It does not dissolve in water. But it does dissolve in most acids and some alkalis. Tellurium also has the unusual property of combining with gold. Gold normally combines with very few elements. The compound formed between gold and tellurium is called gold telluride (Au 2 Te 3 ). Much of the gold found in the earth occurs in the form of gold telluride.

84 Polonium

Discovered in: 1898

Discovered by: Marie Curie

Properties:

It is a radioactive, extremely rare semi-metal. It is reactive, silvery-gray, it dissolves in dilute acids, but it is only slightly soluble in alkalis. it is fairly volatile: about half of a sample of it will evaporate within 3 days (unless it is kept in a sealed container).