chapter 5 : chemical bonding - the great...
TRANSCRIPT
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CHAPTER 5 :
CHEMICAL BONDING
Prepared by KML
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At the end of this lesson, students
should be able to :
(a) Write the Lewis dot symbol for an
atom.
(b) State the octet rule and describe
how atoms obtain the octet
configuration.
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Valence electrons are the outer shell electrons of an
atom. The valence electrons are the electrons that
participate in chemical bonding.
1 1 ns1
2 2 ns2
13 3 ns2np1
14 4 ns2np2
15 5 ns2np3
16 6 ns2np4
17 7 ns2np5
Group # of valence e- e- configuration
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Lewis dot symbol • Consist of the symbol of an element
• One dot for each valence electron in an atom of the element
• Element in the same group have similar outer electron configuration
–Similar Lewis dot symbol
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Group 1 2 13 14 15 16 17 18
Valence
electron
1 2 3 4 5 6 7 8
Lewis
dot
symbol
Li.
: Be
: B .
: C:
..
. N. .
.
: O.
. .
.
: F:
. .
..
:Ne:
. .
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-Atoms combine in order to achieve a more
stable electronic configuration.
-Maximum stability results when an atom is
isoelectronic with a noble gas.
- Atom can achieve noble gas configuration
through :
( a) transfer of electron (gaining or losing)
( b) sharing of electron
OCTET RULE
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THE ELECTRON CONFIGURATION OF IONS
Ions have stable electronic configuration of either:
The noble gas configuration
Pseudonoble gas configuration
Half-filled orbitals
The inert pair effect
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(a) Noble gas configuration
Group 1, 2 and 13 elements transfer valence
e to form cation with noble gas configuration.
Example
Na : 1s22s22p63s1
Na+ : 1s22s22p6 ( isoelectronic with neon )
Mg : 1s22s22p63s2
Mg2+: 1s22s22p6 ( isoelectronic with neon )
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Group 15, 16 and 17 elements accept e to
form anion with noble gas configuration.
Example
O : 1s22s22p4
O2- : 1s22s22p6 ( isoelectronic with neon )
F : 1s22s22p5
F- : 1s22s22p6 ( isoelectronic with neon )
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(b) Pseudo noble gas configuration
-For d block elements, e from 4s orbital will
be transferred first before the 3d electrons.
-d block elements donate electrons to achieve
pseudonable gas configuration
Example :
Zn : 1s22s22p63s23p64s23d10
Zn2+ : 1s22s22p63s23p63d10
( pseudonoble gas configuration )
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Pseudo means false (palsu / menyamar)
So, pseudonoble gas means that the atom
has similar e configuration with noble gases
The valence e configuration needed is either
ns2np6nd10 or ns2np6nd10nf14
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(c) Half-filled orbital
-d block element can also donate or receive e
to achieve half-filled orbitals which is stable
Example :
Mn : 1s22s22p63s23p64s23d5
Mn2+ : 1s22s22p63s23p63d5
( stability of the half-filled orbital)
Fe : 1s22s22p63s23p64s23d6
Fe3+ : 1s22s22p63s23p63d5
( stability of the half-filled orbital)
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(d) The inert pair effect
- elements Group 13 and 14 in Period 5 or 6
form cations with configuration of,
ns2np6nd10(n+1)s2
- This is named the inert pair effect.
Example :
Sn : [ Kr ] 4d105s25p2
Sn2+ : [ Kr ] 4d105s2
( the inert pair effect )