chemistry unit 4.2
TRANSCRIPT
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8/3/2019 chemistry Unit 4.2
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Basics:
Dipole-Dipole forces(permanently polar molecules) + and parts of the molecules attract electrostatically giving Bts higher thanthose of non polar molecules of similar size.
Dispersion/Van der waals forces(non polar molecules)Temporary dipoles form between molecules because of mobile electron
density within the molecule. + on one molecule will induce a on a nearby one and so on, tho theres a net attraction betweenmolecules
Higher forces: More electrons Larger area of contact(larger molecules/atoms) Linear instead of branched chains
There will be bigger van der waals forces as Atomic/molecular size increases More shells of electrons
For large molecules dispersion forces can exceed dipole-dipole attraction
Molecular covalent substances Bonded strongly within themolecule but weakly between molecules
Properties depend on intermolecular forces
Intramolecular bonds Covalent Ionic
Metallic
Intermolecular bonds Van der Waals forces
Dipole dipole attraction
Hydrogen bonds strongest
Ionic bond The electrostatic attraction between + andions
formed by complete transfer of electron/s
Covalent bond Sharing a pair of electrons, one pair to a bond
(rather than complete transfer)
Polarisability The ease with which the electron cloud of an
anion is distorted by a cation so theres electron sharing
Hydrogen bond Electrostatic attraction between a strongly + H atom attached covalently to a highly electronegative element
F/N/O and a strongly F/N/O atom on another molecule, H bonds are longer than covalent bonds- Compounds which can H bond with water are very soluble (glucose, has OH groups that H bond with water)
Strong acidsHCl + water H+ + ClIonise(dissociate)almost completely, nearly every H atom released to become a hydrated proton, lots of H
+(aq) ions
Weak acids H2CO3 + water H
+
+ HCO3
weak acid equilibrium lies to the left so most of the acid wont be ionisedIonise(dissociate)slightly, little H atoms released, little H+(aq)ions
Strong acids and concentrated acids OR weak acids and dilute acids arent the same
Strong weak refers to how much the acid has ionised Concentrated dilute refers to molcm3of the acid
Acids proton donors
Acids mixed with water release H+
which combine with H2O(hydrated)to form hydroxonium ions H3O+
HCl(g) + H2O(l) H+(aq) + Cl
(aq) HCl(g) doesnt release hydrogenions until it meets water so HCl(g) isnt an acid
Bases proton acceptors, make OHhydroxyl ions when dissolved in water
Salt A compound formed by replacing hydrogen in an acid by a metal
The Periodic Table II (Period 3) Variation of properties across a period
Know Period 3 elements reactions with oxygen, chlorine and water
Na Mg Al Si P S Cl Ar
H2OHydrolysis
NaOH+ H2
MgO+ H2
- - - - HCl +HOCl
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O2 Na2O2 MgO Al2O3 SiO2 P4O10 SO2 - -
Cl2 NaCl MgCl2 Al2Cl6 SiCl4 PCl5 S2Cl2 - -
Know the formulae and acid-base character of Na2O, NaOH, MgO, Mg(OH)2, Al2O3, Al(OH)3, SiO2, P4O10, SO2, SO3, Cl2O
and structure/bonding of the oxides
Know the reactions with water of NaCl, MgCl2, AlCl3, SiCl4, PCl3, PCl5, S2Cl2 and structure/bonding of the chlorides
Na2O MgO Al2O3 SiO2 P4O10 SO2 Cl2O
Ionic lattice Ionic covalent
lattice
Giant
covalent
Molecular covalent
NaCl MgCl2 Al2Cl6 SiCl4 PCl3 PCl5 S2Cl2
Giant ionic lattice solidsStrongionic attractions Molecular covalent - weaker intermolecular forces (van der Waals dispersionforces)
Basic Amphoteric Can actboth as acid & base
Acidic
NaCl MgCl2 Al2Cl6 SiCl4 PCl3 PCl5 S2Cl2
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H2O Na+(aq) +
Cl-(aq)
Mg2+(aq)
+
2Cl-(aq)
See below SiO2(s) +
HCl(aq)
H3PO3(aq) +
HCl(aq)
H3PO4(aq) +
HCl(aq)
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Neutral solutions non
vigorous reaction
Covalent chlorides have polar bonds which undergo nucleophilic attack by the lone pair
on the H2O molecule. Reactions violent, fume in moist air(HCl(g))
Na2O MgO Al2O3 SiO2 P4O10 SO2 SO3 Cl2O
H2O NaOH Mg(OH)2 - - H3PO4 H2SO3 H2SO4 HOCl
Na2O
NaOH
MgO
Mg(OH)2
Al2O3Al(OH)3
SiO2 P4O10 SO2 SO3 Cl2O
HCl NaCl
+H2O
MgCl2
+H2O
AlCl3
+H2O
- - - - -
H2SO4 Na2SO4+H2O
MgSO4+H2O
Al2(SO4)3+H2O
NaOH - - a3Al(OH)6 Na2SiO3+H2O
NaH2PO4+H2O
Na2SO3+H2O
Na2SO4+H2O
NaOCl
+H2O
Al2O3+ 6NaOH + 3H2O --> 2Na3Al(OH)6
2 ionic equations showing amphoteric behaviour of aluminium oxide
Al2O3 (s) + 6H+(aq) 2Al3+ (aq) + 3H2O (l)
A12O3 + 6OH + 3H2O 2AI(OH)63
Questions:
What type of bonding would you expect in aluminium fluoride and why?
Ionic Fl ion is very small and has only 1- charge which makes it hard to become polarised
State the type of bonding in sodium oxide and explain how particles react to form the product in Na2O + H2O
2NaOH
Ionic O2 ion very polarisable/strong interaction with polar water reacting with water to give OH
What types of bonding exist in aluminium chloride, Al2Cl6? Dative covalent
NaCl(s) + H2O(l) Na+(aq) + Cl(aq) PCl3 + 3H2O H3PO3 3HClAccount for the difference in the changes by comparing the bonding in these two chlorides.
NaCl is ionic so dissolves in water/ions separate PCl3 is covalent so hydrolyses in water
Relate the acid-base character of the oxides sodium and phosphorus to the variation in metallic character of theelements in Period 3 of the Periodic Table (sodium to argon).
The Periodic Table II (Group 4) Variation of properties down a group
Recall the reasons for increase in metallic character down Group 4
Remember: Metallic character increases- atomic radius increases- ionisation energies fall- ions less polarising
Understand:
- As atoms become larger, they more easily lose electrons to form cations- Increase in metallic bonding, electrostatic attraction between lattice of cations and sea of delocalised electrons
- Increase in strength, malleable, ductile, good conductor of heat & electricity- More able to form ionic bonds with non metals
Recall physical properties of the elementsPhysical propertiesProperties that do not change the chemical nature of matter. Eg color, smell, boiling point
Group 4As atomic number increases, Bt decreases, density increases
AlCl3(s)+ 6H2O(l) [Al(H2O)6]3+
(aq) + 3Cl-(aq)
[Al(H2O)6]3+(aq) [Al(OH)(H2O)5]
2+(aq) + H+(aq)
AlCl3(s)+ H2O(l) AlCl2OH(aq) + HCl(aq)
AlCl2OH(aq) + H2O(l) AlCl(OH)2(aq) + HCl(aq)
AlCl(OH)2(aq)+ H2O(l) Al(OH)3(s) + HCl(aq)
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Carbon (C) Non-metal Solid (graphite) shiny
black
(diamond)
colourless
Conducts along
layers
Non-conductor
Giant covalent layer
lattice
Giant covalent
Silicon (Si) Metalloid Solid dark grey-blue Semi conductor Giant covalent
Germanium(Ge)
Metalloid Solid Grayish white Semi conductor Giant covalent
Tin (Sn) Metal Solid Yellowy-silver Conductor Metallic
Lead (Pb) Metal Solid Grey-silver Conductor Metallic
The oxides acid-base characteristics & equations
CO
CO2
Neutral
Weakly Acidic
Does not react with water. CO + NaOH HCOONaCO2 + H2O --> H2CO3
SiO2 Acidic SiO2 + 2NaOH --> 2Na2SiO3 + H2O
GeO GeO2
SnO SnO2
PbO PbO2
Amphoteric As an acid: XO + NaOH + H2O --> Na2X(OH)4SnO2 + 2NaOH H2O + Na2SnO3
As a base: XO + HCl --> XCl2 + H2O
XO2 + HCl --> XCl4 + H2O
PbCl4 decomposes showing the oxidising nature of lead(IV)oxide
PbCl4 PbCl2 + Cl2
Questions:
Give an equation to show why solutions of carbon dioxide in water are acidic
CO2+H2OH+ + HCO3
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State how the metallic character of the Group 4 elements changes with an increase in atomic number
Increases as atoms become larger (so) more easily lose electrons
As atomic number increases in group 4 the metallic character of the elements increases. Explain how this increase in metallic
character is demonstrated in the acid-base properties of carbon dioxide and of lead(II) oxide
Metal oxides are (more) basic than non-metal oxides CO2 acidic PbO amphoteric
Recall that +2 oxidaton state in Group 4 becomes more stable than the +4 oxidation state down the group and apply this to the
chemistry of tin and lead
Redox (reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number/state changedOxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic
Oxidation describes the loss ofelectrons by a molecule, atom or ion (From +2 to +4)
Reduction describes the gain ofelectrons by a molecule, atom or ion (From +4 to +2)
heatSnO2(s) No reaction
More stable
SnO2doesnt decompose,tin more stable in the +4 ox state
Lead(+2) shows no reducing propertiesLead(IV) oxide oxidises chloride to chlorine
lead(II)chloride
PbO2(s) + 4HCl(aq) PbCl2(s) + Cl(g) + 2H2O(l)
(+4) (+2)reducedheat
PbO2(s) PbO(s) +
O2(g)
More stable
PbO2 decomposes to PbO + O2lead more stable in +2 ox state
Questions:
I SnO2+ 4HClSnCl2+ Cl2+ 2H2O II SnO2+ 4HClSnCl4+ 2H2O
Which of the above reactions is more likely. Explain your reasoning.
Tin is more stable in +4 than +2 oxidation state therefore Sn(IV) not reduced (by Cl-/HCl)
Reasons for the difference in behaviour of SnO2 and PbO2 with concentrated hydrochloric acid
In tin oxidation state +4 more stable than +2
In lead oxidation state +2 is more stable than +4
Therefore lead(IV) oxidises chloride ion (to chlorine)
Recall and explain the structure of carbon tetrachloride
Tetrahedral configuration joined to a carbon atom, in the center, by single covalent bonds. Because of this
symmetrical geometry, the molecule has no net dipole moment; that is, CCl4 is non-polar.
http://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Tetrahedronhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Dipole_momenthttp://en.wikipedia.org/wiki/Image:Carbon_Tetrachloride.svghttp://en.wikipedia.org/wiki/Dipole_momenthttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Tetrahedronhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Electron -
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Recall and explain the behaviour of carbon tetrachloride with water and contrast this behaviour with that of silicon tetrachloride
with water
Chloride(Tetrahalides) Nature
CCl4(tetrachloromethane) Molecular covalent liquid, doesnt hydrolyse CCl4 + 2H2OCO2 + 4HCl
lone pair on oxygen in water cannot attack C atom
because C atom too small / Cl atom too large
SiCl4(silicon
tetrachloride)
SiCl4+ 2H2O SiO2+ 4HCl Carried out in fume cupboard, as HCl is irritant/harmfulMolecular covalent liquid, hydrolyses
due to electron pair donation by water to empty d orbitals of Si atom
Rapid hydrolysis due to electron pair donation by water to empty d orbitals of Si atom In this hydrolysis Si-Cl bonds dont have to be broken before Si-O bonds form
EACT for this hydrolysis therefore much lower than CCl4
Less steric effects in larger molecule
Questions:
Carbon tetrachloride and silicon tetrachloride behave in different ways when added to water. State how each chloride behaves andexplain the difference
SiCl4 reacts/hydrolyses, CCl4 does not
(lone) pair of electrons (from the oxygen atom) in a water molecule
Cannot form a bond with/be donated to the C atom
C is a small atom surrounded by large Cl atoms (so attack is sterically hindered)