Ib Hl Chemistry Assessment Statements Topic 13

Andrew Voyles IB Chemistry Assessment Statements: Topic 13: Periodicity 13.1.1: Na2O, MgO, Al2O3, SiO2, P4O10, P4O6, NaCl, MgCl2, Al2Cl6, and AlCl3 are all solids under standard conditions, due to their strong ionic bonds or network covalent bonds (SiO2, P4O10, P4O6, Al2Cl6, and AlCl3). SO3, Cl2O7, SiCl4, and PCl3 are liquids at room temperature due to their weaker covalent bonds and stronger intermolecular forces. SO2, Cl2O, and Cl2 are gases under standard conditions due to their weaker intermolecular forces. Na2O, MgO, Al2O3, NaCl, and MgCl2 are good electrical conductors in the molten state, as their ionic bonds give up mobile charged electrons when the compounds undergo melting. SiO2, Al2Cl6, and AlCl3 are network covalent compounds and so have no significant conductivity. The other compounds are covalent compounds and do not have mobile electrons to transport charge, so they are not conductors. 13.1.2: NaCl MgCl2 Al2Cl6 SiCl4 PCl3 PCl5 Cl2

Adding H2O NaCl(aq) -> Na+(aq) + Cl-(aq) MgCl2 (aq) -> Mg2+ (aq) + 2Cl- (aq) Al2Cl6 + 6H2O -> 2[Al(H2O)3]+3 + 6HCl (aq) SiCl4 + H2O -> Si(OH)4 + 4HCl (aq) PCl3 + 3H2O -> H3PO3 (aq) + 3HCl (aq) 2PCl5 + 6H2O -> 2HPO3 (aq) + 10HCl (aq) Cl2 (g) + H2O -> HCl (aq) + HClO (aq)

13.2.1: Typical d-block elements contain an incomplete d orbital, and generally exhibit multiple oxidation states (in period 4, with the exceptions of Sc or Zn) ,form colored compounds, form complex ions, and act as catalysts. 13.2.2: Zn is not considered a transition element because both its metal and its common ion (Zn+2) do not have an incomplete d orbital ([Ar]4s23d10 and [Ar] 3d10 configurations, respectively). Sc is similar in that its common ion (Sc+3) does not have an incomplete d orbital ([Ar] configuration). 13.2.3: The multiple oxidation states of the d-block (transition metal) elements are due to the proximity between the 4s and 3d sub shells (in terms of energy). All transition metals exhibit a +2 oxidation state

(both electrons being lost from the 4s) and all have other oxidation states as in the following examples: • • • • •

V : +2, +3, +4, +5 Cr : +2, +3, +6 Mn : +2, +4, +6, +7 Fe : +2, +3 Cu : +1, +2

13.2.4: Ligands are molecules which donate an electron pair to form a dative covalent bond with the central atom, forming a complex ion. 13.2.5: Complex ions are molecules which carry a charge. They are formed around a central atom, with ligands (atoms or molecules) donating an electron pair to form a covalent bond to this central atom. [Fe(H2O)6]3+ : Fe is the central atom, H2O is the ligand. [Fe(CN)6]3- : Fe is the central atom, CN is the ligand. [CuCl4]3- : Cu is the central atom, Cl is the ligand. [Ag(NH3)2]+ : Ag is central atom, NH3 is the ligand. 13.2.6: The color in the transition metals (d-block) is predominantly due to the splitting of the d shell orbitals into slightly different energy levels. As a result, certain wavelengths of energy can be absorbed by the d-block elements (causing electrons to jump between these slightly different energy levels), resulting in the complement color being visible. 13.2.7: D-block elements make good catalysts due to their multiple oxidation states. This gives them the ability to react with different species and produce a path of lower activation energy, and so cause the reaction to proceed at a faster rate. Many examples of these can seen in the following examples. 2 H2O2(aq)

O2(g) + 2 H2O(l)

2 SO2(g) + O2(g) 2 SO3(g) SO3(g) + H2O(l)  H2SO4(aq) N2(g) + 3H2(g)

2NH3(g)

R2C=CR'2 2NO(g) 2CO(g) + O2(g)

R2CHCHR'2 N2(g) + O2(g) CO2(g)

13.2.7: A suitable catalyst will make the reactions more efficient, as they will proceed faster and consume less resources, making them more cost effective.