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7/25/2019 chemistry inorganic
http://slidepdf.com/reader/full/chemistry-inorganic 1/35
Giant molecule
structuresCHM 474
7/25/2019 chemistry inorganic
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Overview……
Bonding Ionic Covalent Metallic
Structure Giant
ionic
Simple
molecular
Giant
covalent
Giant
Metallic
Example Sodium
chloride
Water Diamond Iron
Bonding an
d structure explains the properties ofa substance!
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Macromolecule CrystalsA macromolecule is a big molecule that
contains a network of covalent bondsbinding its particles. he particles arenonmetal atoms. "xamples ofmacromolecules are graphite# diamond#silicon# silicon carbide# silica and boron
Substances withmacromolecular
structures are alwayssolids at room
conditions
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Giant Covalent $tructures
GraphiteDiamond
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Macromolecules……..• %ong chains of molecules
containing a very large number of
atoms
• "xamples& plastics# proteins# somecarbohydrates
• 'igher m.p.(b.p. than simplemolecules due to much strongervan der )aals* forces
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general knowledge about
allotropes. Allotropes are di+erent forms of the same
element with their atoms arrangeddi+erently from one another. hey exhibit
di+erent behavior and characteristics. heconditions that changes allotropic formsare pressure# temperature and light. ,or
example# for carbon to turn into diamond#
we have to heat graphite to a very hightemperature under great pressure . -t is tosimulate the conditions /010 kilometers
down in the "arth*s mantle wherediamonds are formed.
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A%%2324"$
Allotropy 5Gr. allos# other# and tropos#manner6
is a behaviour exhibited by certainchemical elements& these elements canexist in two or more di+erent forms#known as allotropes of that element. -n
each di+erent allotrope# the element7satoms are bonded together in adi+erent manner
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Allotropes ofcarbon
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8iamond
2ne of theallotropes of carbon
‘Allotropes’: Diferent (structural) orms o the
same element‘!sotopes’: Atoms o the same element "ith the
same num#er o protons #ut diferent num#er oneutrons
8iamond is one formof the element carbon.
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8iamondHas a giant co$alent structure
Giant network o car#on atoms heldto%ether #& co$alent #onds in a
tetrahedral arran%ement
'hese our car#on atoms
orm a tetrahedron.
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Diamond
"ach carbon is 9oined to fourother carbon atoms bystrong covalent bonds.
"ach carbon has fourcovalent bonds.
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4roperties of 8iamond:ery high M.4. and B.4.
58iamond melts at about ;<00=C6'ardest natural substance
Reason&Carbon atoms are held together in a giant
rigid structure by strong covalent bonds.
A lot of energy is re>uired to break thesestrong covalent bonds.
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4roperties of 8iamon
8oes not conductelectricityAll electrons are held
in the covalent bonds.
?o ions or freeelectrons to conductelectricity
-nsoluble in water
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8-AM2?8
Carbon has an electronic arrangement of@#/. -n diamond# each carbon shareselectrons with four other carbon atoms forming four single bonds
-n the crystal of diamond#each carbon atom iscovalently bonded to fourother carbon atoms with
CCC bond angles of 01.<o
.he basic unit in diamond istetrahedron where eachcarbon can be made a
centre of a tetrahedron.
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ses of 8iamond
sed in cuttin% other hardsolids (#ecause o its
hardness)*%* Diamond+tipped drills to
cut throu%h roc,
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he physical properties of diam
. has a very high melting point 5almost /000=C6. :erystrong carboncarbon covalent bonds have to bebroken throughout the structure before meltingoccurs.
@. is very hard. his is again due to the need to breakvery strong covalent bonds operating in ;dimensions.
;. doesn7t conduct electricity. All the electrons areheld tightly between the atoms# and aren7t free tomove.
/. is insoluble in water and organic solvents. here areno possible attractions which could occur between
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Graphite
Within the layer
"ach carbon atom is 9oined to threeother carbon atoms by strongcovalent bonds.
Arranged in rings of six atoms
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$tructure of Graphite
Arrangementof carbon
atoms in one
layer
Arrangementof layers
Strong
covalent
bond
Strongcovalent
bond
Weak forcebetween
layers
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G3A4'-"
Graphite is made up of parallel layers5sheets6 of carbon atoms arranged inhexagons
"ach carbon atom has a coordinationnumber of ; which means that it isbonded to three other carbon atoms. hegeometry is trigonal planar with the CCC
bond angles of @0o
Covalent
bonds
Van der Waals
forces
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G3A4'-"Graphite has a
layer structure which is >uitedicult to drawconvincingly in
threedimensions. hediagram belowshows the
arrangement ofthe atoms ineach layer# andthe way thelayers are
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he bonding in graphite
"ach carbon atom uses ; of its electrons to formsimple bonds to its ; close neighbours.
hat leaves a fourth electron in the bonding
level. hese spare electrons in each carbonatom become delocalised over the whole ofthe sheet of atoms in one layer.
he hexagonal layers of graphite are ;./ D apart
and held by weak attractive forces called the:an der )aals forces. hese weak forces areeasily broken# which explains the slippery orsoft nature of graphite. his enables graphiteto be used as solid lubricants as well as
pencils
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'he ph&sical properties o %raphite
. has a high melting point# similar to thatof diamond. -n order to melt graphite# itisn7t enough to loosen one sheet fromanother. Eou have to break the covalentbonding throughout the whole structure.
@. has a soft# slippery feel# and is used inpencils and as a dry lubricant for thingslike locks. Eou can think of graphiterather like a pack of cards each card isstrong# but the cards will slide over eachother# or even fall o+ the pack altogether.)hen you use a pencil# sheets are rubbedo+ and stick to the paper.
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he physical properties ofgraphite
;. has a lower density than diamond. his isbecause of the relatively large amount ofspace that is wasted between the sheets.
/. is insoluble in water and organic solvents for the same reason that diamond isinsoluble. Attractions between solventmolecules and carbon atoms will never bestrong enough to overcome the strongcovalent bonds in graphite.
<. conducts electricity. he delocalised electronsare free to move throughout the sheets. -f apiece of graphite is connected into a circuit#electrons can fall o+ one end of the sheet andbe replaced with new ones at the other end.
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4roperties of Graphite
'he onl& non+metal thatconducts electricit&
Reason:
ach car#on atom hasone electron that is
not used in bonding.
,ree to move A#le toconduct electricit&
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ses of Graphite4encil lead& Made of graphite
and claySince it is soft, it akes o andstick to paper when we write.
%ubricant 5for hot machines6
It does not decompose at hightemperatures.
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4hysical 4roperties ofGiant Covalent$ubstances4hysical state
At room temperature# allsubstances with a giant covalent
structure are solids.$trong covalent bonds make it hard.
M.4. and B.4.'igh M.4. and B.4. because of its
strong covalent bonds
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4hysical 4roperties ofGiant Covalent$ubstances$olubility in water
-nsoluble in water
"lectrical conductivity8o not conduct electricity 5except
graphite!6
Graphite
Diamond
7/25/2019 chemistry inorganic
http://slidepdf.com/reader/full/chemistry-inorganic 28/35Bonding Structure
1. What is the bonding structure of thecompound/element formed by :
a) Sodium toms
b) Chlorine and !otassium
c) Carbon and "#ygen
d) Carbon $in form of diamond)
Giant Metallic Structure
Giant Ionic Structure
Simple Molecular Structure
Giant Covalent Structure
(Metal Metal)-.
(Metal Non-metal)-.
(Non-metal Non-metal)-.
(Non-metal Non-metal)-.
Van der Waal’s Attraction between molecules
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%elting point / Boiling point
&. %ap the compound/element to their
melting point ' boiling point.
/odium 0112 oC 3457 oC
6otassiumchloride
oC30oC
Car#on Dio8ide
+ 7 o
C 3 + 17 o
C
Diamond 772 oC 39452 oC
Stron bond ! Giant metallic structure
Stron bond ! Giant ionic structure
Wea" Van #er Waal’s Attraction
Stron bond ! Giant covalent structure
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)hat are the types of attractive forces present in each of thefollowing substancesF $how how the physical properties arerelated to their structure and bonding.
5a6 8ry ice
5b6 $odium chloride
Answer
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$a) (n dry ice the atoms are *oined together +ithin the molecules by
strong covalent bonds +hile only +ea, van der Waals- forces e#ist
bet+een molecules. he melting and boiling points of dry ice are lo+
since only +ea, van der Waals- forces are needed to be overcome
during the processes of melting and boiling. Besides dry iceconsists of simple molecules +ith no mobile electrons. hus it does
not conduct electricity. Carbon dio#ide is only slightly soluble in +ater
because it is nonpolar in nature.
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$b) Strong ionic bonding e#ists bet+een oppositely charged ions
throughout the +hole lattice of a sodium chloride crystal. hus the
melting and boiling points of sodium chloride are very high.
%oreover sodium chloride is hard since the ions are closely pac,ed
and strong ionic bonds hold the ions together. (t is soluble in +ater
due to the solvation of ions $i.e. the attraction bet+een the ions and
+ater molecules +hich are polar) and is insoluble in nonpolar
solvents. Sodium chloride conducts electricity in the molten or
a0ueous state due to the presence of mobile ions in these states.
Bac
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5b6 8escribe briey how the structures of the followingsubstances are related to their physical properties.
HuartI
Answer
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uart2 is a substance +ith a giant covalent structure. (n the
0uart2 lattice each silicon atom is bonded tetrahedrally to four
neighbouring o#ygen atoms +hereas each o#ygen atom is
bonded to t+o neighbouring silicon atoms. his gives rise to a
tetrahedral diamondli,e structure. s the atoms are held
together by strong covalent bonds a large amount of energy is
re0uired to overcome the strong covalent bonds in the
processes of melting and boiling. hus 0uart2 has high melting
and boiling points. Besides 0uart2 is hard and rigid as the atoms
are fi#ed in their positions by strong covalent bonds. Since there
are no mobile electrons 0uart2 is a poor conductor of heat andelectricity. uart2 is insoluble in both polar and nonpolar
solvents
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