Sulphur: Properties, Electronic structure, Extraction, Allotropes and uses of sulphur

CONTENT

• General Properties of Sulphur Group.
• Electronic Structure of Sulphur Group.
• Extraction of Sulphur.
• Allotropes of Sulphur.
• Uses of Sulphur

GENERAL PROPERTIES OF THE SULPHUR GROUP (GROUP VI ELEMENTS)

The group VI elements include: Oxygen, Sulphur, Selenium, Tellurium and Polonium.

1. Metallic property increases down the group. Oxygen and sulphur are non-metal; selenium and tellurium are metalloid; while polonium is a metal.
2. All the elements are solid except oxygen which is a gas at room temperature.
3. Oxygen and sulphur exhibit allotropy.
4. They have six electrons in their outermost shell. Hence their oxidation number is -2; though sulphur can exhibit -4 and -6 states in some compounds.
5. Electronegativity decreases down the group. Thus, oxygen is a good oxidizing agent.

ELECTRONIC STRUCRURE OF SULPHUR GROUP

Members of the sulphur family include: Oxygen, Sulphur, Selenium, Tellurium and Polonium. Their electronic configurations are shown below: 

Oxygen = 8: 1s² 2s² 2p⁴

Sulphur = 16: 1s² 2s² 2p⁶ 3s² 3p⁴

Selenium= 34: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁴

Tellurium = 52: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁴

Polonium = 84: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁴

SULPHUR

Sulphur is an element. It occurs freely as deposits and in combined state as sulphide and as tetraoxosulphate (IV).

EXTRACTION OF SULPHUR Sulphur is extracted from underground by Frasch process. A three concentric sulphur pump is driven down a hole dug to the sulphur bed. The solid sulphur is melted at 115^oC by super – heated water at 170^oC and 10atms. The molten sulphur is forced out by hot compressed air at 15atm. The molten sulphur is then continuously pumped out and allowed to solidify in a large tank. The sulphur obtained is 99.5% pure.

ALLOTROPES OF SULPHUR

The two main crystalline allotropes of sulphur are:

1. Rhombic sulphur: A bright yellow octahedral crystalline solid. Each crystal is made up of S₈ molecules. Rhombic sulphur is stable below 96^oC.
2. Monoclinic Sulphur: This is amber coloured solid sulphur consisting of needle shaped S₈ crystal. Stable above 96^oC. It easily reverts to Rhombic below 96^oC. The transition temperature between Rhombic and Monoclinic is 96^oC.

Comparison of the Physical Properties of Rhombic and Monoclinic Sulphur

1. Rhombic Sulphur melts at 113^oC;while monoclinic sulphur melts at 119^oC.
2. Rhombic sulphur has bright yellow colour; while monoclinic sulphur has amber colour.
3. Rhombic sulphur has octahedral shape; while monoclinic sulphur is needle-like in shape.
4. Rhombic sulphur is translucent; while monoclinic is transparent.

Sulphur also exists as non – crystalline solid. These are

1. Amorphous sulphur
2. Plastic sulphur

EVALUATION

1. Briefly explain the Frasch process.
2. Name the two allotropes of sulphur and state their transition temperature.

PHYSICAL PROPERTIES

1. Sulphur is a yellow solid.
2. It is insoluble in water but soluble in toluene and carbon (IV) sulphide.
3. It is a poor – conductor of heat and electricity.
4. It melts at 119^oC and boils at 444^oC.

CHEMICAL PROPERTIES

1. It reacts directly with metals to form sulphide (S^2-)

                        Fe_(s) + S_(s)          → FeS_(s)

• It reacts with excess oxygen to form sulphur (IV) oxide

         O_2(g)  +  S_(s)   →  SO_2(g)

• It reacts with hydrogen to form hydrogen sulphide;

                      H_2(g)   +   S_(s) → H₂S_(g)

• It reacts with coke (carbon) to form carbon (IV) sulphide.      

                        C_(s)  +    2S_(s) → CS_2(l)

USES

1. Used in manufacturing tetraoxosulphate (IV) acid
2. Used in vulcanization of rubber
3. Used as germicides
4. Used in manufacturing bleaching agent

GENERAL EVALUATION/REVISION

1. State THREE physical and chemical properties of sulphur.
2. Outline THREE differences between monoclinic and rhombic sulphur.
3. Descried the Frasch process for the extraction of sulphur.
4. State TWO differences between a conductor and an electrolyte.
5. List the steps involve in the treatment of water for municipal supply.

READING ASSIGNMENT

New School Chemistry for Senior Secondary Schools by O. Y. Ababio (6^th edition), page 381-384

WEEKEND ASSIGNMENT

SECTION A: Write the correct option ONLY

1. Sulphur is extracted by (a) Haber process (b) Frasch process (c) Solvay process (d) Contact process
2. Which of the following is a crystalline allotropes of sulphur (a) Monoclinic (b) Plastic (c) Amorphous (d) Colloidal
3. The density of rhombic sulphur is (a) 1.2 (b) 1.5 (c) 2.08 (d) 1.98
4. The shape of monoclinic sulphur is (a) needle shape (b) hexagonal (c) octahedral (d) tetrahedral
5. Sulphur is used for (a) making of cellulose (b) cooking rice (c) vulcanizing rubber (d) manufacturing glass

SECTION B

1. Give three differences between rhombic sulphur and monoclinic sulphur
2. Briefly describe the extraction of sulphur