Page 24 - Chemistry ICSE Class X

12 ICSE Chemistry – 10
Usually the term GNGEVTQP CHſPKV[ means the ſTUV GNGEVTQP CHſPKV[
6JG UWEEGUUKXG GNGEVTQP CHſPKVKGU OC[ DG RQUKVKXG QT PGICVKXG (QT GZCORNG
for the reactions
–1
–
–
O(g) + e o O (g M, OQN (KTUV GNGEVTQP CHſPKV[ Ō M, OQN –1
–1
–
2–
–
O (g) + e o O (g Ō M, OQN 5GEQPF GNGEVTQP CHſPKV[ M, mol –1
Explanation: 1Z[IGP CVQO KU UOCNN KP UK\G CPF KVU PWENGCT EJCTIG KU JKIJ
&WG VQ JKIJ EJCTIG FGPUKV[ KV CEEGRVU CP GNGEVTQP GCUKN[ TGNGCUKPI GPGTI[
–
The O (g) so formed does not accept electron so easily due to
GNGEVTQUVCVKE TGRWNUKQP DGVYGGP VJG NKMG EJCTIGU 6Q HQTEG VJG UGEQPF
–
electron into O (g VJGTGHQTG UQOG GPGTI[ KU TGSWKTGF 6JKU GZRNCKPU YJ[
HQT QZ[IGP VJG ſTUV GNGEVTQP CHſPKV[ KU negative, while the second electron
CHſPKV[ KU positive 6JG GNGEVTQP CHſPKV[ XCNWGU QH UQOG GNGOGPVU CTG IKXGP
KP 6CDNG
Table 1.1 The electron affinity values for some elements (in kJ/mol)
H He
–73 ū
Li Be B C N O F Ne
Ō ū – 23 – 122 Ō – 141 – 328 ū
(+ 780)*
Na Mg Al Si P S Cl Ar
Ō ū – 44 – 120 – 74 – 200 – 349 ū
(+ 590)*
K Ca )C )G As Se Br Kr
Ō ū – 36 – 116 – 77 – 195 – 324 ū
(+ 420)*
Rb Sr In Sn Sb Te I :G
Ō ū – 34 – 121 – 101 – 190 – 295 ū
6JGUG CTG UGEQPF GNGEVTQP CHſPKVKGU

What are the factors affecting electron affinity values
6JG GNGEVTQP CHſPKV[ QH CP GNGOGPV FGRGPFU WRQP VJG HQNNQYKPI HCEVQTU
ƒ Atomic size. Smaller the atom, greater is the magnitude of the
GNGEVTQP CHſPKV[ 6JKU KU DGECWUG VJG CFFGF GNGEVTQP ECP IQ ENQUGT VQ
VJG PWENGWU CPF CU C TGUWNV TGNGCUG OQTG GPGTI[
ƒ Nuclear charge. )TGCVGT VJG PWENGCT EJCTIG larger is the magnitude
QH VJG GNGEVTQP CHſPKV[ 6JKU KU DGECWUG VJG GNGEVTQP YQWNF GZRGTKGPEG
UVTQPIGT CVVTCEVKQP D[ VJG XKTVWG QH JKIJGT PWENGCT EJCTIG
ƒ 'NGEVTQPKE EQPſIWTCVKQP QH VJG CVQO An atom with stable electronic
EQPſIWTCVKQP JCU C NKVVNG QT PQ VGPFGPE[ VQ CFF CPQVJGT GNGEVTQP #U
C TGUWNV UWEJ GNGOGPVU JCXG \GTQ QT PGCTN[ \GTQ GNGEVTQP CHſPKV[ #P
CVQO KU UCKF VQ JCXG C UVCDNG EQPſIWTCVKQP KH
Š #NN VJG QTDKVCNU CTG EQORNGVGN[ ſNNGF
Š #NN VJG QTDKVCNU QH C RCTVKEWNCT GPGTI[ NGXGN CTG JCNH ſNNGF
Š 6JG CVQO JCU C PQDNG ICU EQPſIWTCVKQP K G VJGTG CTG GKIJV
GNGEVTQPU QPN[ VYQ KP VJG ECUG QH *G KP KVU QWVGTOQUV GPGTI[ NGXGN
It is because of the last factor that the noble gas elements have zero
GNGEVTQP CHſPKV[
Periodic Variation of Electron Affinity

6JG XCTKCVKQP QH GNGEVTQP CHſPKV[ KP VJG RGTKQFKE VCDNG KU FGUETKDGF DGNQY