Topic 13 Periodicity HL. Ionic or covalent bonding? Na + Cl - H-Cl Cl-Cl.
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Transcript of Topic 13 Periodicity HL. Ionic or covalent bonding? Na + Cl - H-Cl Cl-Cl.
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Topic 13
Periodicity
HL
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Ionic or covalent bonding?
Na+ Cl-H-ClCl-Cl
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13.1 Trends across third period; Chlorides
• When you go the number of valence electrons increase => increase the number of valence electrons to form bonds.
• NaCl, MgCl2, AlCl3 (Al2Cl6(g)), SiCl4, PCl5 (PCl3 exist),
(sulphur chlorides not required), (Cl2)
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Chlorides of metals (NaCl, MgCl2, AlCl3 )
• Ionically bonded crystalline solids with high melting points.
• Dissolves in water without a chemical reaction to its ions:
NaCl (s) → Na+ (aq) + Cl- (aq)• Conduct electricity in melted or in aqueous
solution.
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Chlorides of non-metals (SiCl4, PCl5 )
• Molecular covalent structure.
• Weak forces between molecules => low melting and boiling points.
• Don’t conduct electricity (no ions and no mobile charges).
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Reacts with water: Hydrolysis
PCl3 + 3 H2O H3PO3 + 3 HCl
Acidic solution
(Phosphoric(III) acid, oxyacid of the element)
H3PO3 + H2O H3O+ + H2PO3-
The oxyacid may also dissociate into acidic oxoniumions.
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• In water the chlorides will conduct electricity; Cl- (aq).• Chlorine, Cl2, if seen as Chlorine chloride, behaves in the
same way:React with water in a hydrolysis reaction
Cl2 + H2O HCl + HClO
• Aluminium chloride reacts as a non-metal chloride due to small size and high charge. It’s very reactive with water:
AlCl3 + H2O Al2O3 + 6 HCl
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Oxides- across period 3
Trend: From basic to acidic characterBase
AcidNa2O, MgO, Al2O3, SiO2, P4O10, SO3 (SO2), Cl2O7 (Cl2O, Cl2O3, Cl2O5)
Ionic Giant Covalent structure
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Left side- oxides are basic
• Na2O + H2O 2 Na+ + 2 OH-
• Magnesium hydroxide only weakly dissociated because of low solubility.
• Reacts with acids (basic oxides):MgO(s) + 2 H+ Mg2+ + H2O
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In the centre- oxides are amphoteric
• Both aluminium and silicon oxides are almost insoluble • Aluminium oxides have amphoteric properties; reacts with both base
and acidAl2O3(s) + 6 H+ 2 Al3+ + 3 H2O
Al2O3(s) + 2 OH- + 3 H2O 2 Al(OH)4-(aq)
• Silicon dioxide can show weakly acidic properties; reacts with strong
alkali to form silicates
• Giant covalent lattices with high melting and boiling points
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To the right in period 3
• Molecular bonding: Gases, liquids or low melting points
• The elements can often form 2 or more oxides with different state of oxidation.
• Reacts with water to form acids.SO3(g) + H2O H2SO4
H2SO4 + H2O H+ + HSO4-
Cl2 + H2O H+ +Cl- + HClO
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13.2 First row d-block elements (Sc Zn) The transition elements
• An element that contain an incomplete d level of electrons in one or more oxidation states
• d-orbitals starts to fill up with electrons• They have some common characteristics
(except Sc and Zn):
– A variety of stable oxidation states– The ability to form ions– Coloured ions– Catalytic activity
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Oxidation states
• The 4s and 3d orbitals are quite close in energy• The electrons in 4s orbitals can easily be lost• Gives stable state to the right of the d-block. To
the left it’s a powerful reductant. (Ti2+ + water Hydrogen)
• Sc to Mn can loose all 4s and 3d electrons and stay stable. More to the right they become strong oxidants
• Highest oxidation state usually occur as oxanions: E.g. dichromate (Cr2O7
2-), permanganate (MnO4-)
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Energy
4s
3d
Mn atom [Ar]4s23d5
4s lower than 3d
4s
3d
Mn2+ ion [Ar] 3d5
4s higher than 3d
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Common oxidation states of the d-block elements
Ti V Cr Mn Fe Co Ni Cu
+7 X
+6 X X
+5 X
+4 X X X
+3 X X X (x) X (x)
+2 (x) X X X X X X X
+1 X
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• All transition elements can show an oxidation number of +2
• You should be familiar withCr (+3, +6), Mn (+4, +7)Cu (+1,+2)
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In solution: Ligand
• Ions of d-block elements have unfilled orbital's. These unfilled orbital's can attract a pair of electrons from an other compound = ligand.
• The ligand must have free (non-bonding) electron pair that they can donate to the ion.
• E.g. H2O, NH3, Cl-, CN-
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In solution: Complex ion
• The ion and the ligand form a dative bond, co-ordinate bond(covalent) bond
• The Ion + ligands = complex ion
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Examples of complex ions• Most complex ions have either six ligands arranged octahedrally around
the central ion (often water or ammonia ligands) or four ligands arranged tetrahedrally (often chloride ligands)
• [Cu(NH3)4]2+ (forms when an excess of ammonia is added to Cu(II)-salt)
• [Ag(NH3)2]+
• [Fe(H2O)6]3+
• [Fe(CN)6]3-
• [CuCl4]2-
• Complex formation can stabilise certain oxidation states and affect the solubility of the ion
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Complexes have often specific colours
• In an isolated atom all d-orbital’s have the same energy.
• The Ligands in a complex ion affect the energy in the d-orbital’s.
• The orbitals split up to two groups with different energy. The energy gap is in the visible region.
• When light going through a transition metal solution energy is absorb when electrons are lifted from the lower level to the higher.
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http://www.chemguide.co.uk/inorganic/complexions/colour.html
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• White light (all colours) hits Copper(II) salt and red and yellow light absorbs => blue-green colour.
• Sc3+ and Ti4+ : no electrons in d-orbitals => colourless
• Zn2+ : filled d-orbital => colourless
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Catalytic activity
• Catalyst is a substance that speeds up a reaction without being consumed by it self. Reduce the activation energy.
• Transition metals often have catalytic behaviour due to:– Ability to form complexes. Close contact.– Many oxidation states. Easy to lose or gain
electrons in redox reactions.
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Homogeneous catalyst
• In the same phase as the reactants• E.g. dissolved ion in water solution
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Heterogeneous catalyst
• On the surface of the metal.E.g.• MnO2, Manganese(IV)oxide: 2 H2O2 2 H2O + O2
• Ni: Alkenes + hydrogen Alkanes
• Fe: Haber process, N2 + 3 H2 2 NH3
The worldwide ammonia production in 2004 was 109 million metric tonnes.[
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• V2O5, vanadium(V)oxide: in the Contact process (manufacture sulphuric acid) 2 SO2(g) + O2(g) 2 SO3(g)
SO3 + H2O H2SO4
Sulphuric acid. 165 million tonnes, with an approximate value of US$8 billion. Principal uses include ore processing, fertilizer manufacturing, oil refining, wastewater processing, and chemical synthesis.
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• Co in vitamin B12
• Pd and Pd in catalytic converters