Modern inorganic chemistry

The elements of

Group III

(Boron, aluminium, gallium, indium, thallium)

Of the five Group III elements, only boron and aluminium are

reasonably familiar elements. Aluminium is in fact the most abund-

ant metal, the third most abundant element in nature, but the other

elements are rare and boron is the only one so far found in con-

centrated deposits.

The data in Table 7.1 show that, as expected, density, ionic radius,

and atomic radius increase with increasing atomic number. How-

ever, we should also note the marked differences in m.p. and liquid

range of boron compared with the other Group III elements; here

we have the first indication of the very large difference in properties

between boron and the other elements in the group. Boron is in

fact a non-metal, whilst the remaining elements are metals with

closely related properties.

Table 7.1

SELECTED PROPERTIES OF THE ELEMENTS

Eletn.

B

Al

Ga

In

Tl

At.

no.

5

13

31

49

81

Outer

electrons

2s^2 2pl

3s^2 3p'

^d^10 4s^2 4p[

4dl()5s^2 5pl

5rf^10 6v^2 6r^1

Atomic

radius

(nm)

0.079

0.143

0.153

0.167

0 171

Radius

o/'M^3 "

(nm)

(0.020)

0.045

0.062

0.081

0.095

Density

g cm ~^3

(293 K)

2.35

2.70

5.91

7.31

11.85

m.p.

(K)

2600

933

303

429

574

b.p.

(K)

2800

2600

2500

2340

1726

lonisation „,-.

energies (kJ

1 st 2nd

801

578

579

558

589

2428

1817

1979

1820

1970

mol ' )

3rd

3660

2745

2962

2705

2880

(V)

-0.87

-1.66

-0.52

-0.34

138