Ci 5.36 Bonding and Structures
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Transcript of Ci 5.36 Bonding and Structures
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BONDING AND
STRUCTURES
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Bonding
Intra
(strong)
Inter
(weak)
Ionic(metal + non-metal)
Covalent(non-metals)
Hydrogen(H attached to
N,O or F)
Dipole forces
Permanent
Dipole
Induced/
InstantaneousDipoles
Metallic
(metals)
TYPES OF BONDING
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Hydrogen Bonding Hydrogen is an exceptional element in that when
it forms a covalent bond its electron is held toone side of the nucleus leaving the other siderelatively bare. Any approaching negatively
charged group can get very close to thehydrogen nucleus and produce an unexpectedlylarge electrostatic attraction.
These electrostatic attractions are exaggeratedwhen H is bonded to a more electronegativeelement e.g. N, F or O. Such electrostaticattractions are called hydrogen bonds.
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Both are explained bythe increased
attraction betweenmolecules caused byhydrogen bondingmaking it more
difficult to separatethem.
For example, in
water. Black dotsrepresent oxygenatoms and white dotsrepresent hydrogenatoms.
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Permanent Dipole Forces
Permanent Dipole
-Dipole Interactions
One part of the molecule is always slightly positive or
negative compared with another part
When molecules that have permanent dipoles cometogether, they will arrange themselves so that the
negative and the positive ends of the molecules attract
one another
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The attractions
are called dipole-dipoleinteractions.
The moleculeseventually align
in order to findthe bestcompromise
betweenattraction andrepulsion.
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Instantaneous Dipole Forces
These are small electrostatic forces that arecaused by movement of electrons within thecovalent bonds of molecules that would
otherwise have no permanent dipole.
As one molecule approaches another theelectrons of one or both are temporarily
displaced owing to their mutual repulsion. Thismovement causes small, temporary dipoles tobe set up which attract one another.
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These dispersion forces
increase with the sizeof the molecule and
with its surface area.
Large molecules with
big surface areas havemore electrons, and
more dispersion forces
and greater attraction
and therefore higherboiling points.
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Question
Which type of dipole do the following
molecules have (explain your reasoning)
Cl2
HCl
CH4
CH3Cl
Poly(ethene)
Poly(propene)
Poly(chloroethene) (PVC)
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Structures
The properties of substances are decided by
theirbonding and structure.
Structure The way atoms are arranged
relative to one another, e.g. Giant Lattice,
Molecular(Simple and Macro).
How does bonding and structure decide
properties?
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For a solid substance
there are three main factors
Type of particle it contains
Atoms, ions or molecules. If a substance contains ions
or polar molecules, it may dissolve in water.
How the particles are bonded together
Ionic, covalent, metallic or weak intermolecular bonds.
The stronger the bonds, the higher the mp/bp of the
substance, and the greater the hardness.
How the particles are arranged relative to each other
One-dimensional chains, two-dimensional sheets or one
of many three-dimensional arrangements.
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Classification of Substances According to Structures (CI 5.6)
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Structure and the Periodic Table
As you go across a period of the PeriodicTable, there is a trend in the structures ofthe element. (fig 37 p.118 CI).
Metallic covalent network covalentmolecules monatomic
Note Carbon exists in two different forms;covalent network (graphite & diamond)and covalent molecules (fullerenes).
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Trends in reactions across a period
Tables 12, 14, 15 p.121 CI 5.6
Reactions with oxygen
In period 3 all elements except argon form oxidesNa2O, MgO, Al2O3, SiO2, P4O10/P4O6, SO3 /2, Cl2O/ Cl2O7
Reactions with chlorine
In period 3 all elements except argon form chlorides
NaCl, MgCl2, AlCl3, SiCl4, PCl5/PCl3, S2Cl2, Cl2
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Reactions with water
Na Vigorous, forms NaOH and H2Mg Only with steam, forms Mg(OH)2 and H2
Al No reaction unless protective oxide layer
removed from surface, forms Al(OH)3 and H2Si No reaction
P No reaction
S No reaction
Cl Dissolves in water (some reacts to form anacidic solution (HCl + HClO))
Ar No reaction
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Acid-base properties of oxides
Acid-base character of oxides is linked to theirstructure.
Giant ionic lattices are basic (Na2O & MgO).
Covalent oxide structures are basic (P4O6, SO3& Cl2O7).
Bonding in Al2O3 has both ionic and covalent
character so it can behave as both an acid and a
base it is Amphoteric.
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Behaviour of chlorides in water
Behaviour of chlorides in water is linked to theirstructure.
Chlorides with giant ionic lattices simply dissolve in water
with no chemical reaction (NaCl & MgCl2).
Chlorides with covalent molecular structures react
(hydrolysed), producing fumes of HCl and forming acidic
solutions (AlCl3, SiCl4, PCl5, S2Cl2).
Complete CI 5.6 q2, 4,5