Chem 1000 Midterm Seven Practice Answers
Question
On the above periodic table:
(a) Indicate the s, p, d and f blocks.
(b) Indicate the general trend of first ionization energy across the rows and down the groups.
(c) Indicate the general trend of the atomic radii across the rows and down the groups.
(d) Indicate the general trend of electronegativity across the rows and down the groups.
s
p
d
f
b) ionization increases left to right and decreases top to bottom
c) Radii decrease left to right and increase top to bottom.
d) Electronegativity increases left to right and decreases top to bottom.
Question Two (6 marks)
The following may have more than one correct answer. Note, the atomic number is given in parentheses.
(a) Which of the following species has the largest ground state radius?
Br (35), Ca2+ (20), H (1), Br- (35), Fe3+ (26)
Br(b) Which of the following elements is the most electronegative?
Cl (17), Cs (55), W (74), Mg (12), Si (14)
Cl is upper rightmost.
(c) Which of the following species has the highest ionization energy?
Mg (12), Co (27), P (15), Mg2+ (12), Fr (87)
Mg2+ has outermost electrons in the lowest n.
(d) Which of the following ions have d subshell valence electrons?
Cl - (17), Na+ (11), Fe2+ (26), U+ (92), Ag+ (47)
Fe3+, U and Ag+
Question Four (three marks)
i) Which of the following elements has the greatest electronegativity: He, K, Co, S or Cl? Explain your
reasoning.
On Pauling’s scale, it is Cl which is upper rightmost.
Question Four (three marks)
Give electron configurations for the following AND indicate whether they are diamagnetic or paramagnetic.
Si
[Ne]3s23p2
paramagnetic
3+
As
[Ar]4s23d10 diamagnetic
Y
[Kr]5s24d1
Question Five (five marks)
i)
Of silane (SiH4) and methane (CH4), which is the bigger molecule? Explain.
Silicon is a larger atom than carbon because its outer (valence) electrons are of a shell of higher n. So silane H
bond will be longer and silane will be the larger molecule.
ii)
Of CI4 and KI, which has the higher boiling point? Explain.
KI had an electronegativity difference that is much greater than that of the CI bonds in CI4. It is an ionic
compound and therefore has a much higher boiling point.
iii)
Of Rb and K, which has the higher first ionization energy? Explain.
The ionization of K involves removing a 4s electron which is lower in energy than the corresponding 5s
electron of Rb. K, therefore, has the larger ionization energy.
iv)
Of P and Cl, which has the greater electron affinity? Explain.
Both of these atoms accept an electron into a 3p orbital, but the larger atomic charge of Cl makes this an orbital
of lower energy that that of P thereby releasing more energy when an electron is added. Cl has the greater
electron affinity.
v)
Of the C—Cl and C—Br bond, which is the strongest? Explain.
Br is larger than Cl so the C—Cl bond will be shorter. Shorter bonds tend to be stronger bonds.
Question Six (three marks)
Complete the following table with respect to the C—N bonds of the three compounds shown.
Bond Order
Bond strength
(kJ/mol)
H3C
NH2
1
~308
~1.45
H2C
NH
2
615
1.29
N
3
~923
1.15
H
C
Question Eight
What is the Pauli exclusion principal?
No two electrons can have the same set of four quantum nos.
Question Six (4marks)
i) Give electron configurations for the following:
Cu
Bond length (Å)
[Ar]3d104s1
Sn2+
[Kr]4d105s25p4
Cl-
[Ar]
ii)
Which of the species above is/are paramagnetic?
Cu and Sn2-
Question Ÿ
You live in the Zborkian Universe which has a different set of fundamental physical laws. The rules for
quantum nos. are the same as our own with the exception that ml can have any value 0, 1, ... l (letter ell).
Sketch the Zborkian Periodic Table up to the end of the 5th shell.
This difference effects the no. of possible orbitals within each subshell.
For l=0, ml = 0 so one s orbital. No change.
For l=1, ml = o and 1 therefore two p orbitals rather than three.
L=2, ml = 0, 1 and 2 therefore only three d orbitals rather than five.
So the s block will look the same, the p block will be only 4 elements wide and the d block will be only 6
elements wide.
Question Three (2 marks)
Of the following bonds, C—Cl and C—Br, which is shorter? Explain your reasoning.
The C—Cl bond is shorter because Cl has a smaller atomic radii.
Question Four (3 marks)
Of PCl5 and MgI2 , which is more likely to be an ionic compound? Explain your reasoning.
The second will have the greatest difference in electronegativity between the two atoms.