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Chapter 6 Ionic compounds
Q1.
Sodium chloride does not conduct electricity in the solid state but it does conduct
when molten.
a How would you use Figure 6.3 on page 94 to explain why solid sodium chloride
does not conduct electricity?
b Explain why molten (liquid) sodium chloride conducts electricity.
A1.
a
b
The diagram shows that in solid sodium chloride, the sodium and chloride ions
are held in fixed positions in the crystal lattice and are not free to move and
conduct electricity.
Molten sodium chloride contains sodium and chloride ions that are free to move
and, therefore, it can conduct electricity.
Q2.
Write the formulas of the ions most likely to form when the following metal atoms
react with non-metals:
a Li
b Na
c Al
d Cs
A2.
a
b
c
d
Li+
Na+
Al3+
Cs+
Q3.
Write the formulas of the ions most likely to form when the following non-metal
atoms react with metals:
a I
b S
c N
d F
A3.
a
b
c
d
I–
S2–
N3–
F–
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Q4.
Write the electronic configurations for the ions most likely to form from the following
atoms. In each case, state which noble gas has the same electronic configuration as the
ion formed.
a Cl
b Mg
c Ca
A4.
a
b
c
1s2 2s2 2p6 3s2 3p6 (Ar)
1s2 2s2 2p6 (Ne)
1s2 2s2 2p6 3s2 3p6 (Ar)
Q5.
Suppose that the atoms of elements with the following electronic configurations form
ions by losing or gaining one or more electrons. In each case, write the formula of the
ion that is most likely to form. (The symbols shown for the elements are not their real
ones.)
a Element M: 1s22s22p4
b Element N: 1s22s1
c Element P: 1s22s22p63s23p1
d Element Q: 1s22s22p63s23p5
e Element R: 1s22s22p63s23p64s1
A5.
The atoms of the metal and the non-metal form ions that have the same configuration
as the nearest noble gas or group 8 element.
a M2–
b N+
c P3+
d Q–
e R+
Q6.
Use diagrams similar to Figure 6.6 on page 97 to show the formation of ions in the
reactions between:
a potassium and fluorine
b magnesium and sulfur
c aluminium and fluorine
e sodium and oxygen
f aluminium and oxygen
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A6.
a
b
c
d
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e
Q7.
Explain why potassium chloride has the formula KCl whereas the formula of calcium
chloride is CaCl2.
A7.
The electronic configuration of an atom of potassium is 1s22s22p63s23p64s1 and that of
an atom of chlorine is 1s22s22p63s23p5. Because an atom of K has one more electron
than an atom of a noble gas and an atom of Cl has one less, in a reaction one K atom
can donate one electron to one Cl atom to give K+ (1s22s22p63s23p6) and Cl–
(1s22s22p63s23p6), both of which have the electronic configuration of the noble gas
argon. The formula of this compound is, therefore, KCl.
Calcium, however, has the electronic configuration of 1s22s22p63s23p64s2. A Ca atom
will lose two electrons to gain a noble gas configuration. Because each Cl atom will
gain only one electron, there will be two chlorine atoms for each Ca atom. This
reaction will therefore produce Ca2+ (1s22s22p63s23p6) ions and Cl– (1s22s22p63s23p6)
ions. The formula of the compound is, therefore, CaCl2.
Q8.
When atoms of potassium react with atoms of oxygen, the changes that occur in the
electronic configurations of each atom may be represented by an equation:
2–
2K(1s22s22p63s23p63s1) + O(1s22s22p4)  2K+(1s22s22p63s23p6
(1s22s22p6)
Write similar equations for the reactions between:
a sodium and chlorine atoms
b magnesium and oxygen atoms
c aluminium and sulfur atoms
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A8.
a
b
c
Na(1s22s22p63s1) + Cl(1s22s22p63s23p5) 
Na+(1s22s22p6) + Cl–(1s22s22p63s23p6)
Mg(1s22s22p63s2) + O(1s22s22p4)  Mg2+(1s22s22p6) + O2–(1s22s22p6)
2Al(1s22s22p63s23p1) + 3S(1s22s22p63s23p4) 
2Al3+(1s22s22p6) + 3S2–(1s22s22p63s23p6)
Q9.
Using the information in Table 6.3 on page 101, write formulas for the following
compounds:
a sodium chloride
b potassium bromide
c zinc chloride
d potassium oxide
e barium bromide
f aluminium iodide
g silver bromide
h zinc oxide
i barium oxide
j aluminium sulfide
A9.
a
b
c
d
e
f
g
h
i
j
NaCl
KBr
ZnCl2
K2O
BaBr2
AlI3
AgBr
ZnO
BaO
Al2S3
Q10.
Using the information in Table 6.3 on page 101, write formulas for the following
compounds:
a sodium carbonate
b barium nitrate
c aluminium nitrate
d calcium hydroxide
e zinc sulfate
f potassium hydroxide
g potassium nitrate
h zinc carbonate
i potassium sulfate
j barium hydroxide
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A10.
a
b
c
d
e
f
g
h
i
j
Na2CO3
Ba(NO3)2
Al(NO3)3
Ca(OH)2
Zn(SO4)2
KOH
KNO3
ZnCO3
K2SO4
Ba(OH) 2
Q11.
Using the information in Table 6.3 on page 101, write formulas for the following
compounds:
a copper(I) chloride
b iron(III) oxide
c copper(II) oxide
d chromium(III) sulfate
e iron(II) oxide
f lead(II) nitrate
g lead(IV) oxide
h tin(II) nitrate
A11.
a
b
c
d
e
f
g
h
CuCl
Fe2O3
CuO
Cr2(SO4) 3
FeO
Pb(NO3)2
PbO2
Sn(NO3) 2
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Q12.
Use the information in Table 6.3 on page 101 to name the ionic compounds with the
following empirical formulas:
a KCl
b CaO
c MgS
d NaF
e Mg(OH)2
f K2O
g FeSO4
h Ba(NO3)2
i NH4Cl
j Na2CO3
k CuSO4
A12.
a
b
c
d
e
f
g
h
i
j
k
potassium chloride
calcium oxide
magnesium sulfide
sodium fluoride
magnesium hydroxide
potassium oxide
iron(II) sulfate
barium nitrate
ammonium chloride
sodium carbonate
copper(II) sulfate
Q13.
Use the information in Table 6.3 on page 101 to write an empirical formula for each
of the following ionic compounds:
a lithium chloride
b calcium carbonate
c ammonium carbonate
d iron(III) sulfide
e sodium dichromate
A13.
a
b
c
d
e
LiCl
CaCO3
(NH4)2CO3
Fe2S3
Na2Cr2O7
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Q14.
This language of chemists is universal. Can you identify the formulas in the figure
below?
Chemical symbols are the same throughout the world.
A14.
Pt; Al2O3; ZnO; O; KOH; HgCl2; NaOH
Q15.
‘Diet-Rite’ Lite Salt, which contains 50% less sodium than table salt, is actually a
mixture of sodium chloride and potassium chloride.
a Write the electronic configuration of the potassium ion in potassium chloride.
b To what group of the periodic table do sodium and potassium both belong?
c Suggest why potassium chloride is a suitable substitute for some of the sodium
chloride.
A15.
a
b
c
1s22s22p63s23p6
group 1
Both elements are from the same group, so the chloride salts should react
similarly.
Q16.
Sodium chloride, or common salt, is an essential part of our diet. Throughout history,
it has also been used to preserve food in the absence of refrigeration. So important
was sodium chloride to daily life that many words or expressions in the English
language have been derived from the word salt. Salary and salinity are two of them.
Can you think of any others?
A16.
Salad; salami; saline; expressions such as ‘salt of the Earth’, ‘take with a pinch of
salt’, ‘worth one’s salt’; and superstitions, such as throwing salt over one’s shoulder to
keep away evil spirits.
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Chapter review
Q17.
Explain why an ionic compound will not conduct electricity in the solid state even
though it contains charged particles.
A17.
In the solid state, ions are held in position by strong ionic bonds and are not free to
move.
Q18.
Describe what happens to the forces between particles as sodium chloride is heated
and melts.
A18.
The strength of the forces remains unchanged, but the kinetic energy of the ions
increases until the forces can no longer hold the ions in the solid lattice, and the lattice
breaks up as the solid melts.
Q19.
The melting temperature of sodium chloride is 801°C whereas that of magnesium
oxide is 2800°C.
a What particles are present in the two solids?
b Which solid has the stronger forces between its particles?
c Give some possible differences in the structure and bonding of the two solids that
would explain the large difference in melting temperature.
A19.
a
b
c
Na+, Cl–; Mg2+, O2–
MgO has the stronger forces between its particles. More energy is required to
overcome the stronger forces. The higher melting temperature therefore reflects
the solid with stronger forces between particles.
The strength of electrostatic attraction between ions will depend on the size of the
ions and on their charge. The Mg2+ ion is slightly smaller than the Na+ ion, and
the O2– ion is much smaller than the Cl– ion. More importantly, the Mg2+ ion and
the O2– ions each have twice the charge of the Na+ ion and the Cl– ion. The
attraction between the ions in MgO is therefore much stronger than in NaCl.
Magnesium oxide therefore has a much higher melting temperature.
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Q20.
Describe an experiment you could carry out to demonstrate each of the following
properties of the compounds given. In each case you should:
i Sketch the equipment you would use.
ii Describe what you would expect to observe.
a Solid magnesium chloride does not conduct electricity.
b Molten sodium chloride is a good electrical conductor.
c Solid sodium chloride is hard and brittle.
A20.
a
b
c
Assemble equipment to test conductivity, such as that shown in Figure 6.5 (page
95). Add a globe to the circuit. When the electrodes are touching the solid
magnesium chloride, the globe will not light up.
Using the same equipment with molten sodium chloride, the globe will glow.
Care is needed, as sodium chloride melts at 801C.
If a crystal of sodium chloride was hit firmly with a hammer, it would shatter.
Again, care is needed—safety glasses must be worn.
Q21.
Use the ionic bonding model to explain the following properties of ionic compounds:
a They generally have high melting temperatures.
b They are hard and brittle.
c They do not conduct electricity in the solid state but will conduct when molten or
dissolved in water.
A21.
The information in Table 6.1 (page 94) is an excellent summary.
a The electrostatic forces of attraction between the positive and negative ions are
strong and will be overcome only at high temperatures.
b The strong electrostatic forces of attraction between the ions mean that a strong
force is needed to break up the lattice, giving the ionic crystals the property of
hardness. However, the crystal lattice will shatter when a strong force is applied,
suddenly causing ions of like charge to become adjacent to each other and be
repelled.
c In the solid state, the ions are not free to move. However, when the solid melts or
dissolves in water, the ions are free to move and conduct electricity.
Q22.
The elements X, Y and Z form ionic compounds when reacted with other elements.
The following compounds are formed: Ca3X2, Y2CO3 and Al2Z3.
a What is the electrovalency (charge) of the ion formed by:
i element X?
ii element Y?
iii element Z?
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b
11
Use these charges on the ions to write correct chemical formulas for the following
compounds:
i the sulfate salt of Y
ii the potassium salt of Z
iii the ionic compound formed between X and Y
iv the ionic compound formed between Y and Z
A22.
a
b
i
ii
iii
i
ii
iii
iv
–3
+1
–2
Y2SO4
K2Z
Y3X
Y2Z
Q23.
Write an empirical formula for each of the following ionic compounds:
a copper(I) nitrate
b silver oxide
c chromium(III) fluoride
d lithium nitride
e potassium carbonate
f magnesium hydrogen carbonate
g nickel(II) phosphate
A23.
a
b
c
d
e
f
g
CuNO3. Copper(I) ion has a charge of +1, nitrate ion has –1.
Ag2O. Silver ion has a charge of +1, oxide ion has –2.
CrF3. Chromium(III) ion has a charge of +3, fluoride ion has –1.
Li3N. Lithium ion has a charge of +1, nitride ion has –3.
K2CO3. Potassium ion has a charge of +1, carbonate ion has –2.
Mg(HCO3)2. Magnesium ion has a charge of +2, hydrogen carbonate ion has –1.
Ni3 (PO4) 2. Nickel ion has a charge of +2, phosphate ion has –3.
Q24.
Name the ionic compounds with the following chemical formulas:
a KF
b LiOH
c ZnCl2
d AlN
e (NH4)2CO3
f Cu(NO3)2
g CrBr3
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A24.
a
b
c
d
e
f
g
potassium fluoride
lithium hydroxide
zinc chloride
aluminium nitride
ammonium carbonate
copper(II) nitrate
chromium(III) bromide
Q25.
Write the empirical formula for the ionic compound formed in the reaction between:
a potassium and bromine
b magnesium and iodine
c calcium and oxygen
d aluminium and fluorine
e calcium and nitrogen
A25.
a
b
c
d
e
KBr. Potassium ion has a charge of +1, bromide ion has –1.
MgI2. Magnesium ion has a charge of +2, iodide ion has –1.
CaO. Calcium ion has a charge of +2, oxide ion has –2.
AlF3. Aluminium ion has a charge of +3, fluoride ion has –1.
Ca3N2. Calcium ion has a charge of +2, nitride ion has –3.
Q26.
Use diagrams to show the electron transfer that occurs when:
a lithium reacts with chlorine
b magnesium reacts with fluorine
c potassium reacts with sulfur
d magnesium reacts with nitrogen
A26.
a
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b
c
d
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Q27.
The electronic configurations of some metallic and non-metallic elements are given
below. (The symbols shown for the elements are not their real ones.) Write formulas
for the compounds they are most likely to form if they react together. The first
example has been done for you.
a A: 1s22s1
B: 1s22s22p4
A2B
2 2 6 2 1
2 2 5
b C: 1s 2s 2p 3s 3p
D: 1s 2s 2p
c E: 1s22s22p63s23p64s2
F: 1s22s22p63s23p4
d G: 1s22s22p63s23p64s1
H 1s22s22p5
2 2 6 2
e K: 1s 2s 2p 3s
L: 1s22s22p4
A27.
a
b
c
d
e
A2B
CD3
EF
GH
KL
Q28.
Refer to the periodic table (page 408) and, for each general formula given, identify
two elements that will react to form an ionic compound with that formula.
(Remember: the metal ion, as represented by X, comes first in each formula.)
a XY2
b XY
c X2Y
d X3Y
e XY3
f X3Y2
A28.
Possible answers are:
a MgCl2 or MgF2
b NaCl or CaS
c Na2O or K2S
d Na3N or Li3N
e AlCl3 or AlF3
f Mg3N2
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Q29.
A student compares the structure and bonding in metals with that in ionic compounds,
and makes the following statements.
a Metals and ionic solids both contain positive ions in a regular arrangement.
b In metals and ionic solids, there is attraction between one particle and all the
neighbouring particles of opposite charge.
c In metals and ionic solids, there will be forces of repulsion between particles with
like charges.
d In metals and in ionic solids that contain metal cations, energy has been used to
remove the valence electrons from metal atoms.
e A metal will conduct electricity whereas an ionic solid will not because electrons
are much smaller than negative ions.
Comment on each of these statements, explaining clearly why you either agree or
disagree.
A29.
a
b
c
d
e
Both metallic and ionic lattices do contain positive ions in a regular arrangement.
In a metallic lattice, the positive ions are surrounded by delocalised electrons; in
an ionic lattice, negative ions alternate with the positive ions.
Agree. In a metallic lattice, each positive ion attracts the delocalised electrons in
its region, and each delocalised electron is attracted to all neighbouring positive
ions. In an ionic lattice, each positive ion is attracted to the negative ions that
surround it, and vice versa.
In a metallic solid, there will be repulsion between the positive ions and between
the delocalised electrons. The particles are arranged to minimise these repulsions.
In an ionic lattice, the arrangement of alternating positive and negative ions also
minimises repulsion between like charges.
Agree. The energy required to remove the outer electron(s) is known as the
ionisation energy, with each electron removed having a specific ionisation
energy. Metals with low ionisation energy, such as sodium and potassium, form
positive ions more readily than metals with high ionisation energies.
Agree. The delocalised electrons are able to move through the lattice of positive
ions due to their small size. The sizes of positive and negative ions in a lattice are
more comparable and neither can move while the lattice structure is intact (i.e.
when the substance is in the solid state).
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Q30.
Construct a concept map to show the connections between the following:
metal, non-metal, atom, valence electron, anion, cation, electrostatic attraction, ionic
bonding
A30.
A possible answer is shown.
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