As binding energy , average binding energy (also dissociation energy , bond cleavage energy , binding energy , Bindungsdissoziationsenthalpie, Valenzenergie ) is in chemistry refers to the amount of energy to be expended, in order, the covalent bond between two atoms to completely cleave a molecule. Two radicals are formed ( homolytic cleavage ). The energy is usually given in joules per mole of the connection and describes the strength of the bond. If all bonds are dissociated, one speaks of atomization energy or atomization heat , which is the total binding energy of a compound. The molar binding energy of ion crystals is described under lattice energy .
The binding energy differs from the standard enthalpy of formation , which proceeds from reactions from the elements in their stable form. The binding energy is not equal to the energy of a heterolytic cleavage ( ionization ), which is significantly greater than that of a homolytic bond cleavage. In physics, the binding energy is usually understood to be the binding energy of an electron to the atom or the binding energy of the atomic nucleus , see binding energy .
The real strength ( true or intrinsic binding energy ) cannot be determined experimentally, since the fragments u. a. the arrangement of their binding partners (in the case of molecules that consist of more than two atoms) and their electronic structure change. Some separation energies can be determined experimentally in individual steps (see example methane ) , other separation energies are calculated from the available data. Known mean binding energies are used for the estimation . Since the intrinsic binding energies are important for the understanding of the chemical binding, theoretical approaches for their determination have been proposed (see Intrinsic binding energies ) .
The size of the bond energy depends, among other things, on the bond length (the longer the lower), the polarity of the bond ( polar atomic bonds are more difficult to split than nonpolar ones) and the type of bond ( single bond is easier than a double bond and this in turn is easier than a Split triple bond ).
table
Dependence of the mean binding energy on the binding length, binding length d in pm, binding enthalpy Δ H in kJ / mol
Halogens with each other
binding
Δ H
d
F − F
159
142
Cl − Cl
242
199
Br − Br
193
228
I − I
151
267
Br − Cl
219
214
Br − F
249
176
Br − I
178
Cl − F
253
163
Cl − I
211
232
with hydrogen
binding
Δ H
d
H − H
436
74
H − C
413
108
H − O
463
97
H − N
391
101
H − P
322
142
H − S
367
134
H − F
567
92
H − Cl
431
128
H − Br
366
141
H − I
298
160
with carbon
binding
Δ H
d
C − C
348
154
C = C
614
134
C≡C
839
120
C − H
413
108
C − O
358
143
C = O
745
122
C − N
305
147
C = N
615
130
C≡N
891
116
C − P
264
184
C − S
272
182
C = S
536
189
C − F
489
138
C − Cl
339
177
C − Br
285
194
C − I
218
214
with oxygen
binding
Δ H
d
N = O
607
O − N
201
136
O − P
335
154
O − F
193
142
O − Cl
208
170
O − Br
234
O − I
234
O = S
420
143
same element
binding
Δ H
d
H − H
436
74
N − N
163
146
N = N
418
125
N≡N
945
110
O − O
146
148
O = O
498
121
P − P
172
221
S − S
255
205
Individual evidence
↑ James E. Huheey: Inorganic Chemistry: Principles of Structure and Reactivity, de Gruyter, Berlin 1988, pp. 1061 ff. ISBN 3-11-008163-6 .
↑ Neufingerl: Chemistry 1 - General and inorganic chemistry , Jugend & Volk, Vienna 2006; ISBN 978-3-7100-1184-9 . P. 47.
