Download Chemistry 235 Semester 04-2008 Homework for Submission #3

Chemistry 235 Semester 04-2008
Homework for Submission #3
Answer the following questions and submit them for marking on or before 30th September 2008 at 2pm in the
chemistry drop box. If any answers show evidence of copying, the whole exercise will attract zero marks.
1) This question concerns the electronic structures of atoms and ions.
a) Draw box diagrams to show the electronic configurations of the following atoms: C, O, Ne, Sc, Cr.
C
(5)
O
Ne
Sc
Cr
b) Write out the electronic configurations of the following ions: F-, Na+, Ti3+, Mn2+, Cu2+.
(5)
2 2 6
F : 1s 2s 3p
Na+: 1s22s23p64s0
Ti3+: 1s22s23p64s03d1
Mn2+: 1s22s23p64s03d5
Cu2+: 1s22s23p64s03d9
c) Which of the above structures show unpaired electrons in the ground state. What magnetic properties
are displayed by atoms or ions with and without unpaired electrons?
C, O, Sc, Cr, Ti3+, Mn2+ Cu2+ have unpaired electrons in the ground state. (3)
Atoms or ions with unpaired electrons are paramagnetic. (1)
Atoms or ions without unpaired electrons are diamagnetic.(1)
2) Explain briefly, in terms of electronic structures, the occurrence of periods, groups, transition series and the
lanthanides and actinides in the periodic table.
(5)
Each periods in the periodic table corresponds to the filling of a new outer shell. e.g. the 5th period corresponds
to the filling of the fifth shell with electrons.
Each main group corresponds to the number of electrons in the valence shell. e.g. group VII elements have
seven electrons in the outer shell. Subgroups have some formal similarities in their chemistry with the main
group elements, but their electronic structures include d-electrons and partially filled penultimate d-orbitals.
Each transitions series corresponds to the filling of a penultimate d-orbital. e.g. in the first transition series the
3d orbitals are filled, although the valence shell is the fourth.
The lanthanide series of elements corresponds to the filling of the 4f orbitals.
The actinide series of elements corresponds to the filling of the 5f orbitals.
3) What are meant by the terms valence state and hybridization of atomic orbitals? (4)
The valence state of an atom is a state which is obtained by promoting an s-electron to an empty p-orbital in the
same shell. This increases the number of bonds that the atom can form.
Hybridisation of atomic orbitals is the mixing of different atomic orbitals in the same shell to give new atomic
orbitals with higher symmetry. Thus an s and three p orbitals can be mixed to give four sp3 hybrid orbitals with
(jointly) tetrahedral symmetry.
What features of molecular structure are explained by them?
(1)
The formation of hybrid orbitals explains the observed shapes of molecules.
Draw diagrams and give examples of molecules containing sp, sp2, and sp3 orbitals (making clear their
geometry) to illustrate your answer.
Give two examples of hybridisation involving d-orbitals, making clear the geometry involved.
sp3d hybridisation gives rise to trigonal bipyramidal symmetry, as in PCl5
sp3d2 hybridisation gives rise to octahedral symmetry, as in SF6
(3)
(3)