SS2 Chemistry Lesson Note on Sulphur

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TOPIC: SULPHUR

CONTENTS:

1. GENERAL PROPERTIES OF GROUP VIA ELEMENT
2. ALLOTROPES AND USES OF SULPHUR
3. COMPOUNDS OF SULPHUR- TRIOXOSULPHATE (IV) ACIDS AND ITS SALTS
4. TETRAOXOSULPHATE (VI) ACID: INDUSTRIAL PREPARATION, REACTIONS AND USES.

PERIOD 1: GENERAL PROPERTIES OF GROUP VIA ELEMENT

Group VIA elements usually called oxygen family have the following properties

• They are made up of oxygen (O), sulphur (S), Selenium (Se) Tellurium (Te) and Polonium (Po)
• Oxygen gas is the first member of the group
• Sulphur comes as the second member of the group and it is a solid, followed by other members.
• They have six valence electrons.
• They gain two electrons usually from group I and II metals to attain octet structure or form negative divalent ions e.g. S₂, O₂
• They form covalent compounds with non-metals e.g. H —–O——–H in water and H—-S—–H , hydrogen sulphide
• Their oxidation states range from -2 in its compounds except peroxides like H₂O₂ and K₂O₂ where oxygent has -1

 ELECTRON STRUCTURE OF SULPHUR

Sulphur is represented with a symbol S, it has 16 atomic numbers. The electronic configuration is 2, 8,6. It is a P block element. Thus have its valence electrons in the p orbital Is² 2s² 2p⁶ 3s²3p⁴

The distribution of electrons into shell is given in the figure below:

Electronic configuration of sulphur

EVALUATION

1. Enumerate any five (5) general properties of group VIA elements.
2. Explain briefly the electron structure of sulphur

PERIOD 2: ALLOTROPES AND USES OF SULPHUR

Sulphur exhibits the phenomenon of allotropy. Allotropy is the existence of an element in two or more different forms in the same physical state. The various forms are known as allotropes. The allotropes of sulphur are Rhombic (or  – sulphur), Monoclinic or prismatic – sulphur), Amorphous sulphur (S- sulphur), Plastic sulphur

Rhombic and monoclinic sulphur are crystalline in nature and are actually important allotropes.

• Rhombic sulphur (α- sulphur): free sulphur exists as allotrope at below 96^oC. It has octahedral structure made up of S₈ The colour is brightly yellow and has a melting point of 113 and density of 2.08gcm^-3

PREPARATION

Rhombic sulphur is prepared by allowing a saturated solution of sulphur in carbon (IV) sulphide (carbon disulphide) in a test tube kept   below C to evaporate slowly. Octahedral crystals will gradually deposit. This preparation should be done in a fume cupboard because of the poisonous and flammability of carbon disulphide

• Monoclinic sulphur (β- sulphur): It is the only stable allotrope between 96^oC and 119^oC and consists of long, thin and needle shaped. The colour is amber. At room temperature it changes to rhombic sulphur crystals. Monoclinic sulphur has a melting point of 119^oC and density of 1.98gcm^-3

PREPARATION

Monoclinic sulphur is obtained by cooling molten sulphur. Powdered sulphur is heated in a crucible till it melts into amber -coloured liquid. More sulphur is added, heated and stirred at the same time. This process is repeated until the crucible is filled with molten sulphur. It is then allowed to cool while a hard crust formed at the top. Piercing one or two holes through the crust and pouring off the remaining molten sulphur reveals a needle shaped crystal of monoclinic sulphur deposited on the sides of the crucible.

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