The Foundations of Chemistry

Figure 6-4 Common hydrides of the representative elements. The ionic hydrides are
shaded blue, molecular hydrides are shaded red, and those of intermediate character are
shaded purple.

6-7 Hydrogen and the Hydrides 253

Thus, hydrogen combines with lithium to form lithium hydride and with sodium to form
sodium hydride.

2Li(
)H 2 (g)88n2LiH(s) lithium hydride (mp 680°C)

2Na(
)H 2 (g)88n2NaH(s) sodium hydride (mp 800°C)

In general terms, the reactions of the heavier (more active) IIA metals may be repre-
sented as

M(
)H 2 (g)88n(M^2 , 2H
)(s) MCa, Sr, Ba

Thus, calcium combines with hydrogen to form calcium hydride:

Ca(
)H 2 (g)88nCaH 2 (s) calcium hydride (mp 816°C)

These ionic hydrides are all basicbecause they react with water to form hydroxide ions.
When water is added by drops to lithium hydride, for example, lithium hydroxide and
hydrogen are produced. The reaction of calcium hydride is similar.

LiH(s)H 2 O(
)88nLiOH(s)H 2 (g)

CaH 2 (s)2H 2 O(
)88nCa(OH) 2 (s)2H 2 (g)

Hydrogen reacts with nonmetalsto form binary molecular hydrides.For example, H 2
combines with the halogens to form colorless, gaseous hydrogen halides (Figure 6-5):

H 2 (g)X 2 88n 2HX(g) XF, Cl, Br, I

hydrogen halides

Specifically, hydrogen reacts with fluorine to form hydrogen fluoride and with chlorine
to form hydrogen chloride:

H 2 (g)F 2 (g)88n2HF(g) hydrogen fluoride

H 2 (g)Cl 2 (g)88n2HCl(g) hydrogen chloride

Hydrogen combines with Group VIA elements to form molecular compounds:

heat

2H 2 (g)O 2 (g)888n2H 2 O(g)

The heavier members of this family also combine with hydrogen to form binary
compounds that are gases at room temperature. Their formulas resemble that of water.

LiH

NaH

KH

RbH

CsH

BeH 2

MgH 2

CaH 2

SrH 2

BaH 2

B 2 H 6

(AlH 3 )x

Ga 2 H 6

InH 3

TlH

CH 4

SiH 4

GeH 4

SnH 4

PbH 4

NH 3

PH 3

AsH 3

SbH 3

BiH 3

H 2 O

H 2 S

H 2 Se

H 2 Te

H 2 Po

HF

IA IIA IIIA IVA VA VIA VIIA

HCl

HBr

HI

HAt

The ionic hydrides are named by

naming the metal first, followed by

“hydride.”

Ionic hydrides can serve as sources of

hydrogen. They must be stored in

environments free of moisture and O 2.

We show LiOH and Ca(OH) 2 as solids

here because not enough water is

available to act as a solvent.

The hydrogen halides are named by

the word “hydrogen” followed by the

stem for the halogen with an “-ide”

ending.

These compounds are named:

H 2 O, hydrogen oxide (water)

H 2 S, hydrogen sulfide

H 2 Se, hydrogen selenide

H 2 Te, hydrogen telluride

All except H 2 O are verytoxic.