Chemistry, Third edition

12 · CHEMICAL FAMILIES

Group 18 elements – the noble gases:

He, Ne, Ar, Kr, Xe, Rn

These elements, with the exception of helium, have the outer electronic configura-

tionns^2 np^6. There is a stable octet of electrons in the outer shells of their atoms.

Group 18 elements have the following properties in common:

1.The elements are all colourless gases.

2.The lighter members of the group do not combine with any substance, xenon

reacts directly only with highly reactive fluorine:

Xe(g)F 2 (g)XeF 2 (s)

Although they are all gases, the elements become more dense as the group is

descended.

12.6

204

Table 12.8Trends in the properties of the halogens and their compounds

Melting and Stability of Colour of Oxidizing

Element Colour boiling points hydrides silver salt ability

F ||increasing ||

Cl |getting ||decreasing white |decreases

Br |darker ||cream |

I   pale yellow 

Halogens

Exercise 12K

Astatine, the fifth halogen, is little studied

because its isotopes are radioactive and

short-lived. From your knowledge of the

physical and chemical properties of the

halogens, predict the physical and chemical

properties of the element. Include:

(i) the colour of the element

(ii) its state at room temperature

(iii) the stability of hydrogen astatide

(iv) its strength as an oxidizing agent

(v) the nature of the bonding present in its

silver salt

(vi) the colour of AgAt.

Compounds of xenon

(i)iiWrite a balanced equation for the reaction of xenon with fluorine to form xenon

tetrafluoride.

(ii)iDraw a Lewis structure for the product of the reaction in (i). What sort of shape would the

molecule have?

(iii)Why are all the fluoride compounds of xenon strong oxidizing agents? What is the

reduction product in these reactions?

Exercise 12L