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Chap 7: Ionic Bonding
Dear students, from here the tricky part of chemistry starts. So
as not to confuse you, I have divided the
chapter of bonding into two parts: ionic bonding, and covalent
and metallic bonding. his lecture deals
only with ionic bonding.
!efore we begin, you all must understand the need for bonding.
"ou see, atoms of many elements are
unstable, i.e. their valence #outermost$ shell is incomplete. %e
have already learnt that atoms try to
complete their duplet or octet, and for this many of them either
gain or lose electrons. &ote that I say
many, not all. his transfer of electrons causes atoms to become
charged, either positively or
negatively' these charged atoms are called ions. (nyway, we all
know opposite charges attract each
other, and thats the whole phenomenon behind ionic bonding. here
is a transfer of electrons between
atoms, and as they become oppositely charged, they attract each
other and a strong bond is formed
between them. his is known as ionic bonding.
Ionic bonding occurs generally between metals of group I and II,
and non)metals of groups *I and *II.
his is because of their configurations. +et us learn why.
Formation:(s I mentioned earlier, atoms try to complete their
duplet or octet, in order to achieve stability. !ut who
gains electrons and who loses them
+et us take the element sodium, which has the configuration
-,,/. "ou can see that it has / electron in its
outermost shell. If it loses that electron, it will achieve
stability. 0owever, it could also gain 1 electrons
and achieve that goal. 2ompare losing the one electron to
gaining S3*3& electrons' what would be
easier 4bviously losing the one it already has. So a metal
#5roup I and II$ will always go for losing its
valence electrons, gaining a positive charge. ( positively
charged ion is known as a cation. 6emember,
metals always form cations.
&ow let us consider 2hlorine. It has the configuration -,,1.
It needs to gain either / electron to complete
its octet, or needs to lose 1 of its own electrons. (gain, the
easier solution would be to gain the oneinstead of losing the
seven, so it will gain, unlike metals. So, non)metals generally
gain electrons to
achieve stability, forming negatively charged ions #anions$.
"ou see in the above e7amples that Sodium loses / electron,
while 2hlorine gains /. %here does the lost
electron go, and where does the gained electron come from "ou
see, the sodium atom gives an electron
to anyone willing to take it, and if we are reacting sodium and
chlorine together, the chlorine accepts theatom that sodium is
giving. here is an e7change of electrons, and opposite charges are
formed #8/ on
sodium and )/ on chlorine$, causing electrostatic attraction
between them that holds them together, and
thus an ionic bond is formed.
his can be shown by a dot and cross diagram.
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9ig 1./. 37change of electrons between &a and 2l
In diagram 1./, you can see that electrons of &a are
represented by crosses, and electrons of 2l by dots.
he electron that 2l gains from &a is also represented by a
cross, to show that a transfer took place. he
bond is then formed due to the attraction between opposite
charges.In 4 levels, ionic bonds are usually shown in this way.
9ig 1.-. Ionic !ond between &a and 2l.
his new compound is totally different from its products. It is
called Sodium 2hloride #&a2l$, also known
as common salt in daily language. 2ompounds formed by ionic
bonding are called ionic compounds,
therefore &a2l is an ionic compound.
&ote: &a2l was ust an e7ample to e7plain the main
concept of ionic bonds. here are many more
e7amples other than this. (lso, &a and 2l do not always bond
together.
Other Examples:
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9ig 1.>. 2ubic +attice of &a2l.
In a cubic lattice, each &a8is bonded to si7 2l ), and each
2l)is in turn bonded to si7 &a8. &o two &a8ions
are placed together, and no two 2l)ions are placed together. his
is why the structure is so strong' there is
attraction from every side which makes it difficult for ions to
break apart.
Chemical Formulae:
he formula of an ionic compound is constructed by balancing the
charges on the positive ions with those
on the negative ions. he positive charges must e?ual the
negative charges. 9or e7ample, in Sodium
2hloride, Sodium #whose symbol is &a$ has charge 8/, while
2hlorine #whose symbol is 2l$ has charge
)/. So / &a needs / 2l, therefore the chemical formula
@&a2lA.
&ow, lets consider
