Page 42 - Chemistry ICSE Class X

30 ICSE Chemistry – 10

Table 2.3 Difference between an atom and an ion
Property Atom Ion
1. Nature of charge Atom is electrically neutral. Ions are electrically charged. Ions given by
metals carry positive charges, while those given
by nonmetals carry PGICVKXG charges.
2. No. of protons An atom contains GSWCN number of protons An ion contains WPGSWCN number of protons and
and electrons and electrons. electrons. The cations have lesser electrons than
protons. The anions have more electrons than
the protons.
3. Size — For any element, the cation is smaller than atom,
and the CPKQP KU DKIIGT than the corresponding
atom.
4. Existence Atoms of noble gases exist as independent Ions can exist independently in solution
atoms. Atoms of all other elements exist in or in the molten electrolyte. In ionic solids,
molecular form. The molecules of elements discrete ions exist but remain bound to their
may contain two, three, four, ... atoms. positions.

Oxidation and Reduction

What is an oxidation-reduction reaction
A reaction in which oxidation and reduction takes place simultaneously is
called an oxidation-reduction (or redox) reaction.

What is oxidation
According to the modern electronic concept, oxidation is a process which
involves the loss of electrons.
2+
ƒ Formation of Cu ion from Cu is an oxidation reaction.
2+
–
Cu o Cu + 2e (loss of two electrons by Cu)
3+
2+
ƒ Formation of ferric (Fe ) ion from ferrous (Fe ) ion is an oxidation
reaction
2+
3+
–
2+
Fe o Fe + e (loss of one electron by Fe )
What is reduction
According to the electronic concept, reduction is a process which involves
͞> K ƚŚĞ ůŝŽŶ ƐĂLJƐ ' Z͟ VJG ICKP QH GNGEVTQPU.
͞>ŽƐƐ ŽĨ ůĞĐƚƌŽŶƐ ŝƐ KdžŝĚĂƟŽŶ͟ 6JG HQNNQYKPI TGCEVKQPU CTG TGFWEVKQP TGCEVKQPU
–
3+
͞'ĂŝŶ ŽĨ ůĞĐƚƌŽŶƐ ŝƐ ZĞĚƵĐƟŽŶ͟ ƒ Fe + e o Fe 2+
ferric ion ferrous ion
–
2+
ƒ Cu + 2e o Cu
cupric ion copper metal
–
ƒ Cl 2 + 2e o 2Cl –
chlorine chloride ion
Oxidation and reduction are reciprocal
Oxidation involves loss of electrons, while reduction involves gain of
electrons. Thus, the oxidation and reduction are reverse of each other.
+P CP QZKFCVKQP TGFWEVKQP TGCEVKQP PQ HTGG GNGEVTQP CRRGCTU KP VJG ſPCN
products; therefore, the electrons lost by an atom or ion must be gained by
other atoms or ions at the same time.
Therefore, the oxidation and reduction must take place
UKOWNVCPGQWUN[ CPF VJG PWODGT QH GNGEVTQPU TGNGCUGF KP VJG QZKFCVKQP
RTQEGUU OWUV DG GSWCN VQ VJG PWODGT QH GNGEVTQPU WUGF WR KP VJG TGFWEVKQP
process.