Page 41 - Chemistry ICSE Class X

Chemical Bonding 29
Q.2. Why do noble gases exist as monatomic molecules?
Ans. 0QDNG ICUGU JCXG UVCDNG GNGEVTQPKE EQPſIWTCVKQPU #VQOU QH VJGUG GNGOGPVU ECPPQV NQUG ICKP QT UJCTG GNGEVTQPU
with other atoms. As a result, the atom of noble gases do not combine and exist as monatomic molecules, i.e., the
noble gases exist in nature as stable free atoms.
Q.3. Which in the following pairs is more stable?
–
2+
+
(a) Ca, Ca or Ca (b) O, O or O 2–
Ans. (a) Ca has an electronic distribution of 2, 8, 8, 2. Thus, Ca atom has two valence electrons. The nearest noble gas
EQPſIWTCVKQP KU 5Q %C CVQO ICKPU UVCDKNKV[ D[ NQUKPI GNGEVTQPU K G YJGP %C CVQO NQUGU VYQ GNGEVTQPU
2+
+
2+
2+
then Ca so obtained becomes very stable. So, out of Ca, Ca and Ca , the Ca is more stable.
D 1Z[IGP CVQO JCU CP GNGEVTQPKE EQPſIWTCVKQP QH 6JG PGCTGUV PQDNG ICU EQPſIWTCVKQP KU 6JWU QZ[IGP
2–
atom gains maximum stability by gaining two electrons. As a result, O is more stable.
+
Q.4. 9JKEJ PQDNG ICU JCU CP GNGEVTQPKE EQPſIWTCVKQP NKMG VJCV QH .K ?
+
Ans. Li JCU C EQPſIWTCVKQP QH - 6JG PQDNG ICU JCXKPI GNGEVTQPU KP KVU QWVGTOQUV UJGNN - UJGNN KU JGNKWO *G
ASSIGNMENT 1
Chemical reactivity and electronic configuration, electron dot structures, octet rule.
ϭ͘ tŚLJ ĚŽ ĞůĞŵĞŶƚƐ ;ĞdžĐĞƉƚ ŶŽďůĞ ŐĂƐĞƐͿ ƐŚŽǁ ĐŚĞŵŝĐĂů ƌĞĂĐƟǀŝƚLJ͍
Ϯ͘ tŚĂƚ ĂƌĞ ;ĂͿ ǀĂůĞŶĐĞ ĞůĞĐƚƌŽŶƐ ;ďͿ ǀĂůĞŶĐLJ͍
ϯ͘ tƌŝƚĞ ƚŚĞ ĞůĞĐƚƌŽŶͲĚŽƚ ƐƚƌƵĐƚƵƌĞƐ ŽĨ ƚŚĞ ĨŽůůŽǁŝŶŐ͗
^ŽĚŝƵŵ͕ ĂƌďŽŶ͕ ŚůŽƌŝŶĞ͕ WŚŽƐƉŚŽƌƵƐ ĂŶĚ KdžLJŐĞŶ
ϰ͘ 'ŝǀŝŶŐ ĂŶ ĞdžĂŵƉůĞ͕ ŝůůƵƐƚƌĂƚĞ ƚŚĞ ŽĐƚĞƚ ƌƵůĞ͘
ϱ͘ ,Žǁ ĚŽ ƚŚĞ ĂƚŽŵƐ ĂĐƋƵŝƌĞ ƐƚĂďůĞ ĐŽŶĮŐƵƌĂƟŽŶ͍

Atoms and Ions

Atoms of certain elements tend to complete their octets either by losing or
by gaining electrons. 6JG EJCTIGF URGEKGU QDVCKPGF YJGP CP CVQO NQUGU QT ĐĂƟŽŶ ;ƉŽƐŝƟǀĞůLJ ĐŚĂƌŐĞĚ ŝŽŶͿ ŝƐ
ICKPU GNGEVTQPU KU ECNNGF CP KQP ĨŽƌŵĞĚ ǁŚĞŶ ĂŶ ĂƚŽŵ ůŽƐĞƐ ŽŶĞ Žƌ
ŵŽƌĞ ĞůĞĐƚƌŽŶƐ͘
How is an ion formed Ŷ ĂŶŝŽŶ ;ŶĞŐĂƟǀĞůLJ ĐŚĂƌŐĞĚ ŝŽŶͿ ŝƐ
ĨŽƌŵĞĚ ǁŚĞŶ ĂŶ ĂƚŽŵ ŐĂŝŶƐ ŽŶĞ Žƌ
When an atom loses one or more electrons, a positively charged ion is ŵŽƌĞ ĞůĞĐƚƌŽŶƐ͘
formed. For example
Na o Na + + e –
sodium atom sodium ion (cation)
When an atom gains one or more electrons, a negatively charged ion
is formed.
–
Cl + e o Cl –
Chlorine atom chloride ion (anion)
Positively charged ion is called cation, and negatively charged ion is
called anion.

How do the properties of an ion differ from those of the
parent atom
The properties of an atom of any element are quite different from those
of its ion. Ion is formed due to loss or gain of electrons from an atom. In dŚĞ ƉƌŽƉĞƌƟĞƐ ŽĨ ƐŽĚŝƵŵ ĂƚŽŵ ;EĂͿ
FQKPI UQ GCEJ CVQO CESWKTGU CP GNGEVTQPKE EQPſIWTCVKQP QH VJG PGCTGUV ĂƌĞ ĞŶƟƌĞůLJ ĚŝīĞƌĞŶƚ ĨƌŽŵ ƚŚŽƐĞ
PQDNG ICU 'CEJ KQP VJWU JCU C UVCDNG PQDNG ICU GNGEVTQPKE EQPſIWTCVKQP #U ŽĨ ƐŽĚŝƵŵ ŝŽŶ ;EĂ Ϳ͘ &Žƌ ĞdžĂŵƉůĞ͕
+
a result, VJG RTQRGTVKGU QH KQPU CTG FKEVCVGF QPN[ D[ VJG GNGEVTKECN EJCTIG QP ƐŽĚŝƵŵ ĂƚŽŵ ;EĂͿ ƌĞĂĐƚƐ ǀŝŐŽƌŽƵƐůLJ
+
–
them. For example, chlorine gas is poisonous, but chloride ion (Cl ) is not. ǁŝƚŚ ǁĂƚĞƌ͕ ǁŚŝůĞ ƐŽĚŝƵŵ ŝŽŶ ;EĂ Ϳ
+QPU FKHHGT HTQO VJG EQTTGURQPFKPI CVQOU CU HQNNQYU ĚŽĞƐ ŶŽƚ ƌĞĂĐƚ ǁŝƚŚ ǁĂƚĞƌ͘