Appearance
Oxygen is the only gas in this Group. It is colourless and odourless. Sulphur is a pale yellow, brittle solid. Selenium can have either an amorphous or a crystalline structure; the amorphous form can be red or black, and the crytalline form can be red or grey. Tellurium is a silvery white colour with a metallic lustre. Polonium is a naturally radioactive element.

Selenium and Tellurium are rare elements with few uses, and along with Polonium will not be considered further. Only Oxygen and Sulphur will be discussed here.

General Reactivity
There is a transition down the Group from non-metallic to more metallic properties, so that Oxygen is a non-metal and Tellurium is a metalloid. All the elements except Polonium form M^2- ions.

Oxygen is the only element in the Group which is able to form multiple bonds. This is due to the small size of its atom. It is also the only element able to participate in Hydrogen-bonding.

Occurence and Extraction
Oxygen occurs widely as the free element in the form of O₂, comprising 21% of the Earth's atmosphere by volume. It also occurs as O₃, Ozone, at high altitudes in the Ozone layer. In the combined form it is found in many minerals, and also in water. Oxygen is obtained industrially by the fractional distillation of liquid air. It is stored under pressure in cylinders.

Sulphur is found as the free element and also as metal sulphide ores and a number of sulphates. Native Sulphur is brought to the surface from underground deposits by the Frasch Process, which uses superheated water to melt the Sulphur and force it upwards.

Physical Properties
The covalent and ionic radii increase going down the Group.

Oxygen occurs as two gaseous allotropes, O₂(Dioxygen or more commonly Oxygen) and O₃ (Trioxygen or Ozone). Oxygen is the more common. It condenses into a pale blue liquid at 90K which is paramagnetic. Ozone is a pale blue, pungent gas which condenses to an inky blue liquid at 161K. The Ozone layer in the upper atmosphere is an important shield against ultra-violet radiation from the sun.

Sulphur has several allotropes, the two main ones being rhombic and monoclinic Sulphur. These are both made up from S₈ molecules.

Chemical Properties
Oxygen is a very reactive oxidising agent, principally in combustion or respiration reactions. Ozone is also a highly reactive and powerful oxidising agent which can cleave the Carbon - Carbon double bond.

Sulphur is reactive in all its forms. It burns in Oxygen with a blue flame to form Sulphur dioxide, SO₂, a pungent, choking gas. With elements of lower reactivity it acts as an oxidising agent and forms sulphides. Sulphur is not as strong an oxidising agent as Oxygen.

Oxides
The most important oxides of Sulphur are Sulphur dioxide, SO₂, and Sulphur trioxide, SO₃. Sulphur dioxide forms when Sulphur is burnt in air or Oxygen, and as all fossil fuels contain Sulphur it is formed when they burn and contibutes to the problem of acid rain. It is a colourless, toxic and pungent gas that dissolves in water to give Sulphurous acid, H₂SO₃. The salts of this acid contain the sulphite ion, SO₃^2-. This ion has an important oxidising reaction to the thiosulphate ion, S₂O₃^2-, which is used for the titrimetric determination of Iodine.

Sulphur trioxide is a volatile white solid that reacts violently with water.

Pure Sulphuric acid, H₂SO₄, is a colourless, viscous liquid. It is a chemically important reagant as it behaves as an acid, an oxidising agent and a dehydrating agent. It is also cheap, and so is used widely in industry.

Halides
The only halide of Oxygen is Oxygen difluroide, OF₂, which is a colourless, toxic gas.

Sulphur has many halides, the most important being Sulphur hexafluoride, SF₆, and Disulphur dichloride, S₂Cl₂

Compounds with Hydrogen
The most important of these is water, H₂O, one of the most versatile of chemicals. It can act as a Bronsted acid or base, a Lewis base, an oxidising agent and a reducing agent.

Hydrogen peroxide, H₂O₂, is a pale blue liquid resembling water in its physical properties as both are extensively Hydrogen bonded. It is a strong oxidising agent.

Hydrogen sulphide, H₂S, is commonly known as 'bad egg gas' because of its smell. It readily dissolves to form a weak acid, and is a strong reducing agent.