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# ALS2A - Section 2 The Electronic Structure of Atoms and the...

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Section 2/ The Electronic Structure of Atoms and the Periodic Table /Suggested solution/ SKH Bishop Baker Secondary School A-Level Chemistry Section 2 The Electronic Structure of Atoms and the Periodic Table 80 IA Q.4 (a) (i) 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 5s 2 [1] (ii) 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 [1] 81 IA Q.4 (a) (2 marks, 1 off for failure to get dip at Al or `peak’ at P; general increase across the period) 81 IB Q.6 (a) From the Lyman series, E 2 - E 1 = 2.466 x 10 15 s - 1 x 6.626 x 10 - 34 J s x 6.023 x 10 23 mol - 1 = 9.839 x 10 2 kJ mol -1 [1] E 3 - E 1 = 2.923 x 10 15 s - 1 x 6.626 x 10 - 34 J s x 6.023 x 10 23 mol - 1 = 11.6627 x 10 2 kJ mol - 1 [1] E 3 - E 2 = (11.6627 - 9.839) x 10 2 kJ mol - 1 [1] From E = h ν Frequency of the first line of the Balmer series = 1.8237 x 10 2 6.626 x 10 - 34 x 6.023 x 10 23 = 4.57 x 10 14 Hz [1] ALTERNATIVE ANSWER : 1 = R ( 1 - 1 ) where m, n = principal quantum numbers λ n 2 m 2 c = velocity of light 2.466 x 10 15 = Rc ( 1 - 1 ) 1 2 2 2 Rc = 2.466 x 10 15 x 4/3 Frequency of the first line of the Balmer series = Rc (1/2 2 - 1/3 2 ) = Rc (5/36) Hz = 2.466 x 10 15 x 4/3 x (5/36) = 4.57 x 10 14 Hz By subtracting frequencies: (2.923 - 2.466) x 10 15 = 4.57 x 10 14 Hz 82 IB Q.8 (a) Emission spectrum : Origin transition (of e - ) from higher energy level to lower energy level. [1] Characteristics discrete energy differences leading to sharp lines of definite wavelengths (frequencies). [2] Characteristic wavelengths depending on nature of the atoms. [1] Absorption spectrum : Origin transition from lower energy level to higher energy level. [1] Emission spectrum : Appearance coloured (bright) lines in dark background. [1] Absorption spectrum : Appearance dark bands (lines) in continuous/coloured background. [1] 1

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Section 2/ The Electronic Structure of Atoms and the Periodic Table /Suggested solution/ 82 IIB Q.10 (a) Ionization energy (or ease of removing one electron) increases along the series and [1] the distortion of electron cloud increases along the series [1] increasing ease of bond formation (do not accept ion formation) [1] increasing chemical reactivities . [1] 83 IB Q.6 (a) (i) The first ionization energy of an atom is the energy required to remove one electron from a gaseous neutral atom and convert it into a positive ion / to infinity. [1] (ii) At the 1s level the electron is very close to the nucleus and high energy is required to remove it. He has a closed shell (1s 2 ) therefore first I.E. is the highest. [1 ½ ] (iii) As the central charge across the same period increases with Atomic number from Li to Ne, the outer electrons are drawn more tightly towards the nucleus, therefore, first ionization energy increases from Li to Ne. [1 ½ ] 84 IA Q.2 (d) (i) Because in undergoing oxidation, Fe 2+ will become Fe 3+ whose electronic configuration has a half-filled 3d subshell which is preferable. [1] ALTERNATIVELY Because Fe 3+ has a half-filled 3d subshell while Fe 2+ does not have. [ ½ ] And because the species having a half-filled subshell is more stable. [ ½ ] Fe 2+ ion is readily oxidized to Fe 3+ ion.
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ALS2A - Section 2 The Electronic Structure of Atoms and the...

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