Sapphires and rubies are forms of the mineral corundum, A1,0g. Corundum is one of the hardest known natural materials.
The hardness of fonic compounds depends on the structure of the crystal
and the strength of the ionic bonds. The distance between the aluminum
lons (AP) and oxide ions (027 is 191 pm. Use Coulomb's law to explain how
the bonding in Al2O, influences its properties.

The scheme below is from a series of reactions that are part of a synthesis of vitamin a. answer the following questions with reference to this scheme. (i) what is "reagent a"? (ii) draw a step-by-step mechanism which explains the formation of compound c from compound b (iii) which reagents would you use to form compound e from compounds c and d (reagents b and c)? for each reagent suggested above in (ii) explain the role of the reagent in the reaction to (iv) form compound e. you may wish to do this by drawing a mechanism. 1. addition of reagent a но reagent a 2. н, о" thо oh нон-с compound a. compound b. compound c .ch-оh 1. reagent b "сно 2. reagent c сh oh compound e. compound d.

Nan element’s square on the periodic table, the number with the greatest numerical value represents the

Which of the following is true about the speed of light? it depends on the wavelength.