Why the noble gases have very low boiling points?

The boiling points of noble gases are very low in comparison to those of other substances of comparable atomic and molecular masses. This indicates that only weak van der Waal forces are present between the atoms of the noble gases in the liquid or the solid state. These vander Waal's forces increases with the increase in atomic size of the atom, and therefore, the boiling points increases from He to Rn . The boiling points follows the trend- He < Ne < Ar < Kr < Xe < Rn .

What are interhalogen compounds?

Interhalogen compounds are formed by the direct combination of different halogen elements under appropriate conditions of temperature and pressure. They are regarded as the halide of more electropositive halogen, with the halogen having less electropositive character. Iodine has the maximum tendency to form interhalogen compounds whereas Fluorine does not form any interhalogen compounds as a central atom. General Formal : XX n ' where n = 1 , 3 , 5 or 7 For example: XX ' ( ClF , BrF ) XX ' 3 ( ClF 3 , BrF 3 ) XX 5 ' ( ClF 5 , IF 5 ) XX ' 7 ( IF 7 )

Fluorine exhibits only - 1 oxidation state whereas other halogens also show + 1 , + 3 , + 5 and + 7 oxidation states. Explain.

Halogens can get the noble gas configuration either by gaining one electron to form uninegative ion, or by sharing electrons with other atoms. Thus, they show an oxidation of state of - 1 or + 1 . Since fluorine is the most electronegative element, it always shows an oxidation state of - 1 . It does not show any positive oxidation state.The other elements also show positive oxidation states of + 1 , + 3 , + 5 and + 7 . The higher oxidation states of chlorine, bromine and iodine are due to the presence of vacant d -orbitals in their valency shells. The oxidation states of + 4 and + 6 occur in oxides and oxoacids of chlorine and bromine and + 7 oxidation state occurs in interhalogen compounds such as IF 7 . Thus, the halogens exhibit the following oxidation states :

Oleum is known by two names: Fuming sulphuric acid and disulphuric acid. As the name suggests, it has two sulphuric acid molecules bound together. So, the formula is H 2 S 2 O 7 . Structure of Oleum:

What happens when potassium chlorate is heated with manganese dioxide?

When potassium chlorate ( KClO 3 ) is heated in the presence of a manganese dioxide catalyst, it decomposes to form potassium chloride and oxygen gas. KClO 3 → MnO 2 KCl + O 2

Why is H 2 O a liquid and H 2 S a gas at normal temperature?

H 2 O a liquid and H 2 S is a gas at normal temperature due to high electronegativity of oxygen and its small size, there are strong hydrogen bonding in water. As a result, the molecules exists as associated and is liquid at room temperature. But there is negligible hydrogen bonding in H 2 S because of low electronegativity of sulphur. Fig- Structure showing hydrogen bonding in water.

Explain why NO 2 dimerises.

NO 2 dimerises to N 2 O 4 because it is unstable as it contains odd number of electrons. Therefore, NO 2 is paramagnetic, while N 2 O 4 is diamagnetic in which two unpaired electrons get paired.

Arrange the following in. the order of increasing bond dissociation enthalpy : F 2 , Cl 2 , Br 2 , I 2

The smaller enthalpy of dissociation of F 2 compared to that of Cl 2 whereas X-X bond dissociation enthalpies from chlorine onwards show the expected trend: Cl – Cl > Br – Br > I – I. A reason for this anomaly is the relatively large electron-electron repulsion among the lone pairs in the F 2 molecule where they are much closer to each other than in the case of Cl 2 . Hence, the correct order for bond dissociation enthalpy is Cl 2 > Br 2 > F 2 > I 2 .

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