The Foundations of Chemistry

REACTIONS OF THE FREE HALOGENS

The free halogens react with most other elements and many compounds. For example,

all the Group IA metals react with all the halogens to form simple binary ionic compounds

(Section 7-2).

General Reaction Remarks

nX 2 
2M88n2MXn All X 2 with most metals (most vigorous reaction with

F 2 and Group IA metals)

X 2 
nX 2 88n2XXn Formation of interhalogens (n1, 3, 5, or 7); X is

larger than X

X 2 
H 2 88n2HX With all X 2.

3X 2 
2P88n2PX 3 With all X 2 , and with As, Sb, Bi replacing P

5X 2 
2P88n2PX 5 Not with I 2 ; also Sb88nSbF 5 , SbCl 5 ;

As88nAsF 5 ; Bi88nBiF 5

X 2 
H 2 S88nS
2HX With all X 2

X 2 
2X88n2X
X 2 F 2 88nCl 2 , Br 2 , I 2

Cl 2 88nBr 2 , I 2

Br 2 88nI 2

The most vigorous reactions are those of F 2 , which usually oxidizes other species to

their highest possible oxidation states. Iodine is only a mild oxidizing agent (Iis a mild

reducing agent) and usually does not oxidize substances to high oxidation states. Consider

the following reactions of halogens with two metals that exhibit variable oxidation

numbers.

With Fe With Cu

2Fe
3F 2 88n 2FeF 3 (only)

2Fe
3Cl 2 (excess) 88n 2FeCl 3 Cu
X 2 88n CuX 2 (XF, Cl, Br)

Fe
Cl 2 (lim. amt.) 88n FeCl 2

Fe
I 2 88n FeI 2 (only) 2Cu
I 2 88n 2CuI (only)

Fe^3 

I 88n Fe^2 

^12 I 2 Cu^2 

2I88n CuI
^12 I 2

THE HYDROGEN HALIDES AND HYDROHALIC ACIDS

The hydrogen halides are colorless gases that dissolve in water to give acidic solutions

called hydrohalic acids. The gases have piercing, irritating odors. The abnormally high

melting and boiling points of HF are due to its very strong hydrogen bonding (Figure

13-5).

24-6

24-5

948 CHAPTER 24: Some Nonmetals and Metalloids

 3

 3 
 2

 1

 1

 2

 2

Bromine reacts with powdered
antimony so vigorously that the
flask vibrates.

Iron and chlorine react to form
iron(III) chloride, FeCl 3.

For instance, aqueous solutions
of hydrogen fluoride are called
hydrofluoric acid.