Worked solutions to textbook questions
Chapter 3 The periodic table
E1.
To which block of the periodic table does:
a plutonium belong?
b roentgenium belong?
AE1.
a
b
f-block
d-block
E2.
a
b
Give the name and chemical symbol for each of the elements: 99, 100, 101 and
102.
In honour of whom were each of the elements in part a named?
AE2.
a
b
einsteinium Es, fermium Fm, mendelevium Md, nobelium No
Albert Einstein, Enrico Fermi, Dmitri Mendeleev, Alfred Nobel
Q1.
Use the periodic table (Figure 3.2, on page 39) to answer the following questions.
a In which group of the periodic table will you find the following?
i B
ii Cl
iii Na
iv Ar
v Si
vi Pb
b In which period of the periodic table will you find the following?
i K
ii F
iii He
iv P
v H
vi U
c What is the name, symbol and electronic configuration of:
i the second element in group 14?
ii the second element in period 2?
iii the element that is in group 18 and period 3?
A1.
a
i
ii
iii
iv
v
vi
group 13
group 17
group 1
group 18
group 14
group 14
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b
c
i
ii
iii
iv
v
vi
i
ii
iii
4
2
1
3
1
7
silicon, Si, 2,8,4 or 1s22s22p63s23p2
beryllium, Be, 2,2 or 1s22s2
argon, Ar, 2,8,8 or 1s22s22p63s23p6
Q2.
Use the periodic table to predict the number of valence electrons for each of the
following:
a Ba
b Br
c Cs
d Te
e Ge
A2.
The valence electrons are those in the outer shell of an atom.
a 2
b 7
c 1
d 6
e 4
Q3.
Suppose you were familiar with the properties, reactions and compounds formed by
the following elements: sodium, chlorine, magnesium, argon and sulfur. Which
element would you use to predict the properties of the following?
a krypton
b selenium
c fluorine
d potassium
e barium
A3.
Look for elements in the same group and/or period in the periodic table.
a argon
b sulfur
c chlorine
d sodium
e magnesium
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Q4.
Name an element with similar properties to those of:
a potassium
b barium
c selenium
d boron
A4.
a
b
c
d
lithium, sodium, rubidium, caesium or francium
beryllium, magnesium, calcium, strontium or radium
oxygen, sulfur, tellurium or polonium
aluminium, gallium, indium or thallium
Q5.
In which block in the periodic table are elements with the following ground state
electronic configurations located? Name the period and group, where appropriate.
a 1s22s22p63s2
b 1s22s22p2
c 1s22s22p63s23p63d54s2
d 1s22s22p63s23p4
A5.
a
b
c
d
s-block, period 3, group 2
p-block, period 2, group 14
d-block, period 4
p-block, period 3, group 16
Q6.
Name the period and group of each of the following elements:
a the element with a +3 charged ion that has an electronic configuration of
1s22s22p6
b the element with an excited atom that has an electronic configuration of
1s22s22p63s13p6
c the element with a –2 charged ion that has an electronic configuration of
1s22s22p63s23p6
A6.
a
b
c
period 3, group 13
period 3, group 17
period 3, group 16
Q7.
Why are elements arranged in the periodic table in order of atomic number rather than
relative atomic weight?
A7.
Atoms are listed in the periodic table in order of atomic number because the atomic
number determines the number of electrons, and this in turn sets the properties that
make each element unique. The relative atomic mass does not relate directly to either
atomic number or electron number.
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Q8.
Explain in you own words:
a the meaning of the term electronegativity
b the meaning of the term core charge
c the relationship between electronegativity and core charge
A8.
a
b
c
Elecronegativity is a measure of the electron-attracting ability of an atom.
Core charge is the charge experienced by an outershell electron in an atom. Core
charge takes account of the nuclear charge, but allows for the shielding effect of
the inner-shell electrons.
As core charge increases, electronegativity increases.
Q9.
Figure 3.8 on page 43 gives electronegativity values for the elements of groups 1, 2
and 14–17 of the periodic table.
a Give the symbol and name of the element that has:
i the highest electronegativity
ii the lowest electronegativity
b In which group do we see:
i the greatest change in electronegativity as we go down the group?
ii the smallest change in electronegativity as we go down the group?
c Why are the elements of group 18 usually omitted from tables that give
electronegativity values?
A9.
a
b
c
i F
ii Fr
i group 17
ii group 1
Elements in group 18, the noble gases, have a very stable electronic configuration
and so are unreactive.
Q10.
a
b
Explain in your own words the meaning of ionisation energy.
What factors need to be considered when predicting the trend in ionisation
energies across a period?
A10.
a
b
Ionisation energy is the least amount of energy needed to remove an electron
from an atom or ion.
The factors that affect ionisation energy across a period are the size of the atom
(i.e. the distance of the outermost (highest energy) electron from the nucleus), and
the charge on the nucleus.
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Q11.
Elements and compounds are classified as pure substances.
a What is meant by the term pure substance?
b In what ways are elements and compounds similar?
c In what ways do elements and compounds differ?
A11.
a
b
c
A pure substance is one with a fixed formula.
Elements and compounds are both pure substances. This means that the
composition is consistent throughout and each can be represented by a specific
formula. This makes pure substances different from mixtures, which can be
separated into their components by physical processes.
In an element, all atoms are chemically identical. In a compound, two or more
elements are chemically combined in a fixed ratio. The elements of a compound
cannot be separated by physical means (such as filtration).
Q12.
Sodium chloride contains 39.3% sodium. Calculate the mass of:
a sodium in 15.6 g of sodium chloride
b chlorine in 3.5 kg of sodium chloride
c sodium chloride that contains 5 g of sodium
d sodium that will be combined with 2.75 g of chlorine
A12.
a
b
c
d
Mass of sodium = (39.3% of 15.6) g
= 15.6 × 39/100 g
= 6.13 g
Percentage of chlorine in sodium chloride = (100 – 39.3)%
= 60.7%
Mass of chlorine in 3.5 kg = (3.5 × 60.7/100) kg
= 2.1 kg
Mass of sodium chloride = mass of sodium × 100/39.3
= 5 × 100/39.3 g
= 12.7 g
From the percentages we know:
39.3 g of sodium combines with 60.7 g of chlorine
2.75 g of sodium combines with x g of chlorine
2.75/39.3 = x/60.7
 x = 60.7 × 2.75/39.3
 mass of chlorine = 4.25 g
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Q13.
a
b
Refer to Table 3.6 on page 49 and identify two properties that clearly indicate
sodium chloride is chemically different from sodium and chlorine.
Refer to Table 3.7 on page 49 and identify the key property that indicates
hydrogen, oxygen and water are three different chemicals.
A13.
a
b
Every pure substance has a precise melting temperature. Sodium and chlorine
(elements) and sodium chloride (a compound) are classified as pure substances.
As the melting temperature of sodium chloride is quite different from those of
sodium and chlorine, we can conclude that sodium chloride is chemically
different from sodium and chlorine.
In addition, the pattern of electrical conducting behaviour of sodium chloride in
the solid and gas states differs from the behaviour of sodium and chlorine.
The different melting temperatures indicate that hydrogen, oxygen and water are
different chemicals.
Q14.
Sulfur is the element below oxygen in group 16 of the periodic table. Predict the
formula of the compound formed between hydrogen and sulfur.
A14.
The compound commonly formed between oxygen and hydrogen has the formula
H2O. As sulfur is in the same group as oxygen, we would predict the compound
between sulfur and hydrogen to have the formula H2S.
Q15.
Consider elements that make up the following compounds. Which of the compounds
are likely to have properties similar to those of sodium chloride?
a calcium oxide (CaO)
b sulfur dioxide (SO2)
c hexane (C6H14)
d potassium bromide (KBr)
A15.
Potassium bromide (KBr) because potassium is in the same group as sodium (group 1)
and bromine is in the same group as chlorine (group 17).
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Chapter review
Q16.
In the modern periodic table (Figure 3.2, on page 39), explain why:
a there are two groups of elements in the s-block
b there are six groups of elements in the p-block
c there are ten elements in each transition series
d there are fourteen elements in the actinides and the lanthanides
A16.
a
b
c
d
Elements in the s-block are filling an s-subshell. As an s-subshell accommodates
a maximum of two electrons, there are only two groups of elements in the sblock. They have outer shell configurations of s1 and s2.
Elements in the p-block are filling a p-subshell. As a p-subshell accommodates a
maximum of six electrons, there are six groups of elements in the p-block. They
have outer shell configurations of s2p1–s2p6.
Elements in the d-block are filling a d-subshell. As a d-subshell accommodates a
maximum of ten electrons, there are ten elements in each transition series.
The lanthanides and actinides are filling an f-subshell. As an f-subshell
accommodates a maximum of fourteen electrons, there are fourteen elements in
each of these series.
Q17.
Sketch an outline of the modern periodic table, indicating the four main blocks. Label
your diagram to indicate:
a the shell that is being progressively filled as you move across each period
b the subshell that is being filled in each of the main blocks
A17.
s-subshells
1st shell
2nd shell
3rd shell
4th shell
5th shell
6th shell
7th shell
p-subshells
d-subshells
f-subshells
Lanthanides
Actinides
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Q18.
Name an element with properties similar to those of:
a carbon
b rubidium
c iodine
d phosphorus
A18.
The elements with properties to these will be those closest to them in the same group.
a silicon
b potassium, caesium
c bromine
d nitrogen, arsenic
Q19.
In his version of the periodic table, Mendeleev arranged elements in order of
increasing atomic weight but placed tellurium (atomic weight 127.6) before iodine
(atomic weight 126.9).
a Suggest why he did this.
b Why is tellurium located before iodine in the modern periodic table?
A19.
a
b
Mendeleev placed tellurium before iodine because this placed both tellurium and
iodine with elements that were chemically similar.
In the modern periodic table, elements are arranged in order of increasing atomic
number. The atomic number of tellurium is one less than the atomic number of
iodine.
Q20.
Gallium is an element in group 3, period 4 of the periodic table. By reference to the
table, predict:
a whether the element is a metal or non-metal
b whether a compound formed from the reaction of gallium and oxygen will have
properties similar to those of sodium chloride or those of water
A20.
a
b
In the p-block, the elements become more metallic as you go down a group.
Aluminium, which is immediately above gallium, is a metal, so we would predict
gallium would also be a metal.
Gallium oxide is a compound formed when a metal (gallium) reacts with a nonmetal (oxygen). This would lead us to predict its properties would be more like
those of sodium chloride (also a compound of a metal and non-metal) than those
of water (a compound of two non-metals).
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Q21.
As you move across a period, the number of subatomic particles in an atom increases
but the size of an atom decreases. Why?
A21.
As one moves from left to right across groups 1, 2 and 13–17, the charge on the
nucleus increases. Each time the atomic number increases by one, the electrons are
attracted to an increasingly more positive nucleus. Within a period, the outer electrons
are in the same shell—that is, they have the same number of inner-shell electrons
shielding them from the nucleus. Therefore, the additional nuclear charge attracts the
electrons more strongly, drawing them closer to the nucleus and so decreasing the size
of the atom.
Q22.
Account for the fact that it takes more energy to remove an electron from the outer
shell of atoms of:
a phosphorus than magnesium
b fluorine than iodine
A22.
a
b
Magnesium and phosphorus, with outer electrons in the third shell, are in the
same period. Magnesium has a nuclear charge of +12 but, with completed inner
shells of 1s22s22p6, the outer electrons experience the attraction of a core charge
of +2. The outer-shell electrons of phosphorus, which has a nuclear charge of +15
and the same number of inner shells as magnesium, are attracted by a core charge
of +5. The stronger attraction of the phosphorus electrons to the core means that
more energy is required to remove an electron from a phosphorus atom than from
a magnesium atom.
Both fluorine and iodine are in group 17 so the outer electrons of each atom
experience the attraction of the same core charge. Because the outer-shell
electrons of a fluorine atom are closer to the nucleus than those of an iodine atom,
they are attracted more strongly and so more energy is needed to remove one.
Q23.
Consider the elements in period 2 of the periodic table: lithium, beryllium, boron,
carbon, nitrogen, oxygen and fluorine. Describe the changes that occur as you move
across the period. Consider:
a the sizes of atoms
b metallic character
c electronegativity
A23.
As you move across period 2 from lithium to fluorine:
a the radius of the atoms decreases as the core charge increases
b there is a trend from metals (lithium, beryllium) to non-metals (boron, carbon,
nitrogen, oxygen and fluorine)
c electronegativity increases as the core charge increases and size of the atoms
decreases
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Q24.
Chemists once called the group 18 elements the ‘inert gases’. Why is this name less
popular now?
A24.
Xenon and krypton will form some compounds, particularly with oxygen and fluorine,
so the term inert does not accurately describe krypton and xenon. Hence, the term
‘noble gases’ is used.
Q25.
How do chemists explain the very low reactivity of the noble gases?
A25.
Each of the noble gases has eight electrons in its outer shell. Chemists recognise this
as a stable configuration that is associated with negligible electronegativity values and
very high ionisation energies. Chemical reactions, which involve the rearrangement of
outer-shell electrons, would disrupt this stability, so reactions of the noble gases are
very unusual and limited to krypton and xenon.
Q26.
Beryllium reacts with oxygen to form beryllium oxide, formula BeO. Predict the
formulas of the oxides of the other elements in group 2.
A26.
MgO, CaO, BaO, SrO
Q27.
If calcium oxide is 71.5% calcium and 28.5% oxygen, calculate:
a the mass of calcium in 4.6 g of calcium oxide
b the mass of oxygen in 0.46 g of calcium oxide
c the mass of oxygen you would need to react with 10 g of calcium to form calcium
oxide
A27.
a
b
c
Mass of calcium is 71.5% of 4.6 g
= 4.6 × 71.5/100 g
= 3.3 g
Mass of oxygen = 0.46 × 28.5/100 g
= 0.13 g
Mass of oxygen = 10 × 28.5/71.5 g
= 4.0 g
Q28.
Suppose you reacted 10 g of calcium with 10 g of oxygen until all of the calcium was
converted to calcium oxide. Use your answer to Question 27c to calculate the mass of
oxygen you would have left over after the reaction.
A28.
From Question 27 we know that 10 g of calcium requires 4 g of oxygen to convert it
to calcium oxide. Therefore, if 10 g of oxygen is reacted with calcium until all of the
calcium has reacted, there would be 6 g of oxygen remaining.
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Q29.
Mendeleev used the properties of elements to help him form groups in his periodic
table.
The following table gives some properties of elements that have been labelled W, X,
Y and Z. In each case, decide if the element is most like sodium or chlorine in its
reactions with other elements. (You may need to refer to Table 3.6 on page 49.)
Element Melting temperature
W
64C
X
–39C
Y
119C
Z
1540C
A29.
W is most like sodium
X is most like sodium
Y is most like chlorine
Z is most like sodium
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Property
Compound formed when W reacts with oxygen;
conducts electricity when molten.
Element X conducts electricity in solid and
liquid states.
Compound formed when X reacts with fluorine;
does not conduct electricity when molten.
Compound formed when Z reacts with fluorine;
conducts electricity when molten.
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Q30.
What concepts or ideas are the two versions of the periodic table in Figure 3.15 on
page 52 trying to convey? Search the Internet for other versions of the periodic table.
A30.
Students’ own answers.
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