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MSE160 2014 Quiz 1 (Ver.2) Solutions

# 4 marks boron b has five electrons therefore the fifth

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Unformatted text preview: 2.18x10- 18 J can be generalized to any one electron atom or ion with atomic number Z by the expression En =- bZ2/n2. Using this model, calculate the fifth ionization energy of B in kJ/mol. [4 marks] Boron (B) has five electrons, therefore the fifth ionization energy would be the energy required to remove the last electron. At this point, Boron is a one electron ion (B4+) which means we can use the above equation. The removal of an electron from a one electron atom/ion corresponds to raising the electron to the Bohr orbit of n = ∞. Therefore, the 5th ionization energy (IE5) can be described as the difference between energy levels of the n=1 and n=∞ Bohr orbits. -bZ 2 -bZ 2 IE 5 = 2 - 2 n1 n2 ! 1 1\$ 1 IE 5 =- ( 2.18x10 -18 J ) ( 52 )# 2 - 2 & but 2 → 0, so "∞ 1 % ∞ ! 1\$ IE 5 =- ( 2.18x10 -18 J ) ( 52 )#- 2 & "1% IE 5 = ( 5.45x10 -17 J/electron ) ( 6.022x10 23 electrons/mol) IE 5 =32800 kJ/mol 4. Sketch how the potential energy changes for two hydrogen atoms as a function of distance of separation (r). Please label your axis, the bond energy of H2, and bond length of H2. [4 marks] See text page 365. Page 2 of 2...
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