Page 44 - Chemistry ICSE Class X

32 ICSE Chemistry – 10
Formation of various types of bonds is described below.

Electrovalent (or Ionic) Bond

The compounds such as sodium chloride (table salt) and potassium nitrate
(nitre) are typical ionic compounds.

What is an ionic bond
Ŷ ĞůĞĐƚƌŽǀĂůĞŶƚ ;Žƌ ŝŽŶŝĐͿ ďŽŶĚ ŝƐ
ĨŽƌŵĞĚ ďLJ Ă complete transfer ŽĨ The coulombic force of attraction between the two oppositely charged ions
ŽŶĞ Žƌ ŵŽƌĞ ĞůĞĐƚƌŽŶƐ ĨƌŽŵ ƚŚĞ ĂƚŽŵ is called an electrovalent (or ionic) bond.
ŽĨ ĂŶ ĞůĞŵĞŶƚ ƚŽ ƚŚĂƚ ŽĨ ĂŶŽƚŚĞƌ The positively charged ion is called cation and the negatively charged
+
ĞůĞŵĞŶƚ͘ ion is called anion. An electrovalent (or ionic) bond between a cation A ,
ͻ and an anion B is commonly described by writing the cation and anion
–
dŚĞ ĂƚŽŵ ǁŚŝĐŚ ůŽƐĞƐ ŽŶĞ Žƌ ŵŽƌĞ together, viz., A B .
+ –
ĞůĞĐƚƌŽŶƐ ŐŝǀĞƐ Ă ĐĂƟŽŶ͕ ǁŚŝůĞ ƚŚĞ
ĂƚŽŵ ǁŚŝĐŚ ŐĂŝŶƐ ŽŶĞ Žƌ ŵŽƌĞ
ĞůĞĐƚƌŽŶƐ ŐŝǀĞƐ ĂŶ anion͘ How is an electrovalent (or ionic) bond formed
(QTOCVKQP QH CP KQPKE DQPF VCMGU RNCEG VJTQWIJ VJG HQNNQYKPI UVGRU
Step 1: Atom of one of the elements loses one or more electrons to form a
+
cation, e.g., an atom A loses one electron to form a cation A .
loses an
+
A o A e –
atom electron anion electron
Step 2: The atom of the other element gains one or more electrons to form an
–
anion, e.g., an atom B gains one electron to form an anion B .
gains an
–
B + e o B –
electron
atom electron anion
Step 3: The cation and anion so formed come closer and are held together by
the electrostatic force of attraction, i.e., the two ions are bound by an
ionic bond.
–
+ –
A + + B o A B
cation anion electrostatic force of attraction
/ƚ ƐŚŽƵůĚ ďĞ ƌĞŵĞŵďĞƌĞĚ ŚĞƌĞ ƚŚĂƚ keeps these ions together, hence
ĚƵƌŝŶŐ ƚŚĞ ĨŽƌŵĂƟŽŶ ŽĨ ĞůĞĐƚƌŽǀĂůĞŶƚ give rise to an electrovalent bond
ďŽŶĚ͕ ƚŚĞ ƚŽƚĂů ŶƵŵďĞƌ ŽĨ ĞůĞĐƚƌŽŶƐ What are the characteristics of an electrovalent
ůŽƐƚ ďLJ ŽŶĞ Žƌ ŵŽƌĞ ĂƚŽŵƐ ŽĨ ĂŶ
ĞůĞŵĞŶƚ ŝƐ ĂůǁĂLJƐ ĞƋƵĂů ƚŽ ƚŚĞ ƚŽƚĂů (or ionic) bond
ŶƵŵďĞƌ ŽĨ ĞůĞĐƚƌŽŶƐ ŐĂŝŶĞĚ ďLJ ŽŶĞ #P GNGEVTQXCNGPV QT KQPKE DQPF JCU VJG HQNNQYKPI EJCTCEVGTKUVKEU
Žƌ ŵŽƌĞ ĂƚŽŵƐ ŽĨ ƚŚĞ ŽƚŚĞƌ ĞůĞŵĞŶƚ͘
ƒ An electrovalent bond is formed due to the coulombic attraction
between positively and negatively charged ions.
ƒ An electrovalent bond is non-directional. This is because coulombic
forces act equally in all directions.
ƒ An electrovalent bond gets broken when an electrovalent compound
is dissolved in a polar solvent such as water, or when melted.
What are the conditions that favour the formation of an
electrovalent (or ionic) bond
Formation of an electrovalent (or ionic) bond involves the following
RTQEGUUGU
ƒ Formation of a cation. An atom of the electropositive element
loses electron(s) to give a positively charged ion (cation). This is an
endothermic process, and requires energy equal to the ionisation
GPGTI[ of the element.
ƒ Formation of an anion. An atom of the electronegative element gains
electron(s) to form a negatively charged ion (anion). This process
is usually exothermic and energy equal to the GNGEVTQP CHſPKV[ is
released.