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Species with "Eighteen + Two" Valence Electron

These species are generally composed of heavy elements. 81Ti element found as Ti3+

cation, the system of 18 valence electrons are quite stable. However, Ti cations with the

electron configuration 3!"r# $d1%$f1$&s'&p!

&d1%!s', was also found and even more stable

than Ti3+ cations. This configuration system stability often attributed with the fact full all

filled orbitals, specifically (nown as the electron configuration of the )18 + ') system or in

terms of species with inert electron pair. *lements a, n, and Tl -group 13, e, /n, and 0b

-group 1$, and s, /b, and 2i -group 1& can be formed sequentially +, '+, and 3+ions,

typically with inert electron pair, -$4! s'.

The role of the inert electron pair to the stability of the ion in the group turned out to be

stronger with increasing atomic number. 5or e6ample Tl+, sequentially more stable than n+

dan a+7 /n$+is more stable than /n'+7 but otherwise 0b'+is more stable than 0b$+. n group

1&, /b

3+

and 2i

3+

fairly stable, li(ewise /b

&+

7 however, 2i

&+

is less stable.

Species with Various Electron Valence

ons of this type consists of transition elements of d andf group which has an electronic

configuration d and f is not full. enerally, these ions have the 8418 outer electronic structure.

That is ns'np

!nd

-%41%with n 3, $, &. n addition, the transition group elements are (nown to

form cations with various o6idation state.

roupfelements, lantanoide and a(tinoide, that each has the electronic configuration ... 4f(1-14)

5s

2

5p

6

5d

(0-1)

6s

2

, dan ... 5f

(1-14)

6s

2

6p

6

6d

(0-1)

7s

2

. 2y removing theoutermost electron, that is (n-1)d(0-1)ns2 , these elements produce 3+ cation that more

stable with leave the 8 valence electron configuration, but with varying amounts of electrons

inside is not full, (n-2)f(1-14)

. The stability of the transition ions and the inner transition,

generally associated with the comple6 compounds formation.

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The Ion formation tendency

The sequence of si6 types of ion stability is that the type of the electronic configuration of

noble gases is most stable, followed by eighteen electron configuration type7 ion with the

transition elements configuration type and the inner transition is most unstable. The more

stable the structure of the ion configuration, the less tendency the ion to form comple6 ion.

The question that appear immediately is what are the factors that support the formation of an

ion9 enerally it can be predicted that the level of ease of an ion formation is influenced by

three main factors, that is:

1 ion electronic configuration stability that is concerned, the more stable configuration is

formed more easily an element forming the ion,

' ion charge, the smaller the ionic charge ions more easily formed, and

3 ion si;e, the greater the si;e of the cation and the smallest anion si;e, the both are more

easily formed.

therwise,

on the formation the anion, small atoms relatively stronger bind the electrons7 for the halogen

group, for e6ample, the 5 atom is easier to form the 5 4ions than =l atom, and so 2r and .

Physical properties of Ionic Species

The above description discuss about the release and binding of electrons to form positive ions

and negative ions in the molecule compounds. f conditions do not allow for the formation of

specific ions, thus, the communion of electrons will occur and a covalent bond is formed. The

transition from the ionic nature to the covalent nature is depend on several factors. =riteria

for the determination of both types of such properties can be based on the physical properties

of the concerned species. onic compounds generally have relatively high boiling point and

melting point, and is a good conductor of electricity in the molten or solution state. ?elatively

high boiling point due to the relative amount of energy needed to brea( the =oulomb forcesbetween ions while the electrically conductive properties caused by the movement of ions in

the melt or solution.

Two species e6treme e6ample is ionic compound @a=l and covalent

compounds ==l$. ccording to the polari;ation theory developed by

5aAan, when two ion is close to each other forming a cloud of electrons,

the anion will be affected by the pull of cations, and at the same time

the nucleus of anions and the nucleus of cation will repel each other.

This will resulted the anions deformation or polari;ation as illustrated

by 5igure 3.1

+ambar 3.1 2entu(- ion normal, dan

-2 terpoplarisasi

-

2

-+

+

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n general, the cation si;e is much smaller than the of anions, therefore the polari;ation

properties of the cations are also much smaller than the polari;ation of anions. The important

thing to (nown is that this polari;ation effect results in electrons especially valence electrons

are no longer fully affected by one of ion or atom. but distributed so that is influenced by

both ion or atom are concerned. The greater the influence of both atoms simultaneously, thesmaller the degree of ionic nature and the greater the degree of covalent nature of the

concerned species. This effect can be formulated as the following description.

1 The amount of the charge. ?ising ionic charge resulted in an increase of polari;ed

nature of the counterion, thus lowering ionic properties and covalent properties

species....