Graphite is one of the crystalline forms of carbon. Two of the distinctive properties of graphite are: It conducts electricity even though it is a non-metal, and It can act as a lubricant even though it has a giant covalent structure. Give a brief explanation of these properties in light of the structure of graphite. Graphite are as lubricant.

Each carbon atom in a graphite layer is joined to three other carbon atoms by strong covalent bonds to form flat hexagonal rings. The various layers of carbon atoms in graphite are quite far apart so that no covalent bonds can exist between them. The various layers of carbon atoms in graphite are held together by weak van der Waals forces. Since the various layer of carbon atoms in graphite are joined by weak forces, they can slide over one another it is the softness of the graphite which make it useful as a lubricant.

HARD

Upper Secondary-IGCSE

IMPORTANT

Earn 100

Astatine is very rarely seen.What would your predict to be its physical state and colour at room temperature and pressure?

Important Questions on Elements and Compounds

HARD

Upper Secondary-IGCSE

IMPORTANT

Cambridge IGCSE Chemistry Workbook 4th Edition>Chapter 3 - Elements and Compounds>Exercise 3.1>Q e

The element within a group tends to show clear trends in its physical properties as you go down the group. The following solid element in group VI shows this. Complete the table by filling the gaps. Use the following value when filling in the missing values.

685 4.79 0.198 450 0.221

Name of element	Sulphur	Selenium	tellurium
Density/g/cm³	2.07	_____	6.24
Melting point / ^oC	115	221	_____
Boiling Point / ^oC	445	_____	988
Ionic radius /nm	0.184	_____	_____

HARD

Upper Secondary-IGCSE

IMPORTANT

Cambridge IGCSE Chemistry Workbook 4th Edition>Chapter 3 - Elements and Compounds>Exercise 3.3>Q a

Plot a graph of the melting and boiling point of the halogens against their proton numbers. Join the points for each property together to produce two separate lines on the graph.
Draw a line across the graph at

20 ° C

(room temperature) to help you decide which elements are solid, liquid or gas at room temperature and pressure.

HARD

Upper Secondary-IGCSE

IMPORTANT

Cambridge IGCSE Chemistry Workbook 4th Edition>Chapter 3 - Elements and Compounds>Exercise 3.3>Q c

Which of the halogen are gases at room temperature and pressure?