School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
General Principles of Chemistry – CHEM110
Tutorial 8 – 24th and 26th April 2013
Inorganic Chemistry
Atomic Radii
1.
Arrange the following atoms in order of increasing atomic radius: Na, Be, Mg.
Answer: Be < Mg < Na
Atomic and Ionic Radii
2.
Arrange the following in order of decreasing size: Mg2+, Ca2+, and Ca.
Cations are smaller than their parent atoms, and so the Ca2+ion is smaller than the Ca atom.
Because Ca is below Mg in group 2A of the periodic table, Ca2+ is larger than Mg2+.
Consequently, Ca > Ca2+ > Mg2+.
3.
2–
2–
Which of the following has the largest radius: S , S, O ?
Answer: S
2–
S is below O in the periodic table, S is larger than O. Anions are larger than their parent atoms,
2–
and so the S ion is larger than the S atom.
Ionic Radii in an Isoelectronic Series
4.
2–
Arrange the ions K+, Cl-, Ca2+, and S in order of decreasing size.
First, we note that this is an isoelectronic series of ions, with all ions having 18 electrons. In such a
series, size decreases as the nuclear charge (atomic number) of the ion increases. The atomic
numbers of the ions are S (16), Cl (17), K (19), and Ca (20).
2–
–
+
Thus, the ions decrease in size in the order S > Cl > K > Ca2+,.
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Reasoning : Consider the trends within ions
For isoelectronic cations: the greater the positive charge, the smaller the ion
For isoelectronic anions: the greater the negative charge, the larger the ion
Periodic Trends in Ionisation Energy
5.
Referring to a periodic table, arrange the following atoms in order of increasing first
ionisation energy: Ne, Na, P, Ar, K.
Ionisation energy increases as we move left to right across a row.
It decreases as we move from the top of a group to the bottom.
Because Na, P, and Ar are in the same row of the periodic table, we expect IE to vary in the order
Na < P < Ar.
Because Ne is above Ar in group 8A, we expect Ne to have the greater first ionization energy: Ar <
Ne. Similarly, K is the alkali metal directly below Na in group 1A, and so we expect IE for K to be
less than that of Na: K < Na.
From these observations, we conclude that the ionization energies follow the order
K < Na < P < Ar < Ne
Qxides
6.
Classify the oxides: CaO, SO3, FeO, SiO2, Al(OH)3, NO2, and ClO2 into:
(i)
Acidic
(ii)
Basic and
(iii)
Amphoteric
oxides:
i)
Acidic - SO3,SiO2, NO2 and ClO2
ii)
Basic - : CaO and FeO
iii)
Amphoteric - Al(OH)3
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A resultant borderline between basic and acidic oxides occurs along a diagonal.
Properties of s- and p-Block Elements
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
Ga
Ge
As
Se
Br
Rb
Sr
In
Sn
Sb
Te
I
Cs
Ba
Tl
Pb
Bi
Po
At
Basic Oxides
7.
Amphoteric Oxides
Acidic Oxides
Complete and balance the following equations. Also identify the product as an oxide,
superoxide, peroxide or hydroxide. Include the phases of the products.
(i)
4Li(s) + O2 g)
(ii)
Ca(s) + 2H2O (g)
Heat
(iii) 2Ba (s) + (excess) 2O2 (g)
2Li2O(s) (oxide)
Heat
Ca(OH)2(aq) + H2(g) (hydroxide)
Heat
2BaO2(s) (Peroxide)
Additional Questions
8.
Write chemical equations to illustrate the amphoteric nature of
(i)
HCO3-
(ii)
ZnO
(i) HCO3- is amphoteric as it reacts in both basic and acidic media.
Reactions with acid:
HCO3- + H+ → H2CO3
Reactions with base:
HCO3- + OH- → H2O + CO32-
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(ii) ZnO reacts with both acids and with bases:
In acid: ZnO + 2H+ → Zn2+ + H2O
In base: ZnO + H2O + 2OH- → [Zn(OH)4]2Electronegativity
9.
Give the general rule regarding the acidity/basicity of oxides.
The more electronegative the central atom, the more acidic the oxide.
10.
Put the following in order of INCREASING electronegativity:
phosphorus, cobalt, zinc, rubidium, oxygen
Electronegativity will increase from left to right in a period and from bottom to top
in a group.
Hence the order is: Rb, Co, Zn, P, O
Acid Strength
11.
Name two factors that affect the acid strength of oxoacids.
Factors that determine the strength of oxoacids are:
1. The electronegativity of the central atom
2. The no. of terminal O atoms in the acid molecule
12.
Determine which is the stronger acid in each of the following pairs?
(i) HIO3 or HBrO3
(ii) HClO4 or H2SO4
(iii)HNO2 or HNO
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i) HIO3 or HBrO3
Lewis Dot
Structure:
Same number of oxo type
oxygen atoms
I is less electronegative
Same number of oxo type oxygen atoms
Br is more electronegative
Stronger acid
ii) HClO4 or H2SO4
Lewis Dot
Structure:
More oxo type oxygen
atoms
Fewer oxo type oxygen atoms
Stronger acid
iii) HNO2 or HNO
Lewis Dot
Structure:
Same number of oxo type
oxygen atoms
Same central atom, so the same
electronegativity
H bonded to the more
electronegative O, stronger acid
Same number of oxo type oxygen atoms
Same central atom, so the same electronegativity
H bonded to the less electronegative N
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Industrial Process
13.
Give a brief summary of the contact process. Use equations in your answer.
(Refer to your notes)
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