Why PCl3 is called phosphorus trichloride but AlCl3 is aluminium chloride?

Answer 1

Aluminium has a valency of 3 and forms a compound called aluminium chloride with chlorine . It is stable . But phosphorus has a valency of 3 and 5. Hence , it is called phosphorous trichloride and phosphorous pentachloride.

Answer 2

Because Aluminium only exhibits one oxidation state at '+3'.

However, Phosphorus exhibits two oxidation states viz. '+3' and '+5'.

Hence to distinguish between oxidation states we have

PCl3 = Phosphorus trichloride ( ox'd state +3)

PCl5 = Phosphorus pentachloride (ox'd state +5).

Many none-metals and the transition metal exhibit variable oxid'n states, so the name of compounds is used to indicate different oxidation states.

e.g. a non=metal

Sulphuric Acid (H2SO4) is '+6' for sulphur

Sulphurous Acid (H2SO3) is '+4' for sulphur.

For a transition metal

Ferrous oxide (FeO) ( Iron (II) oxide ) is '+2' for iron

Ferric oxide (Fe2O3) ( Iron (III) oxide is '+3' for iron.

Answer 3

The naming convention for binary ionic compounds involves using the element name followed by "-ide" (e.g. chloride). For covalent compounds, the prefixes indicate the number of each atom present (e.g. trichloride for PCl3). The naming rules are different for different compound types.

Answer 4

Correctly is also aluminium trichloride.