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Aids
to chemistry - Metals and non-metals
review
Francine
Taylor Campbell, Contributor
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| Members
of the William Knibb Memorial
High Schools' Challenge Quiz Team
are, from left, Vennell Miller,
Shamane Campbell, Isaac Benjamin
and Krishane Johnson.
- Carlington Wilmot Photo |
REVIEW
OF POINTS
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Metals are elements, which form ions
by losing or giving up electrons.
They form positive ions or cations.
This makes them good reducing agents.
*
The reactivity of a metal is based
on how readily it will give up its
valence electrons. The farther away
the outer electron is from the attractive
pull of the nucleus, the more readily
it will be lost.
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The reactivity series arranges metals
in order of their reaction with oxygen,
water and dilute acids. A more reactive
metal will displace a less reactive
metal from a solution of its salt.
*
Metals exhibit the following physical
properties; high melting and boiling
points, good conductors of heat and
electricity and generally solids which
are malleable and ductile.
LET
US NOW EXAMINE A FEW QUESTIONS.
1.
(a) List three physical properties
of metals.
(b)
Sodium and rubidium (Rb) are metals
in Group 1 of the Periodic Table.
Sodium is in Period Three and rubidium
is in Period Five.
(i)
Write the molecular formula for the
hydroxide, nitrate and carbonate of
rubidium.
(ii)
How would you expect the compounds
in (b) (i) above to react when heated?
(iii)
What method could be used to extract
rubidium from its ore? Give one reason
for your answer.
(iv)
A small piece of rubidium was placed
into distilled water. State two observations
that you would expect to make. A piece
of red litmus, placed in water at
the end of the experiment, changed
to blue. Explain this observation.
ANSWERS
1.
(a)Three physical properties of metals
are conductors of heat and electricity
and high melting and boiling points.
(b)
(i) Rubidium hydroxide - RbOH, Rubidium
nitrate - RbNO3, Rubidium carbonate
- Rb2CO3
COMMENT:
Rubidium is in group 1 of the periodic
table, along with sodium, therefore
it has one electron in its outer shell
and will form the +1 ion (Rb+1) like
sodium. To form the compounds, just
consider the charges on the ions and
bring them together so that the charges
cancel.
(ii)
Based on the fact that rubidium will
undergo similar reactions like sodium,
we would expect the carbonate and
hydroxide of rubidium to be stable,
that is not decomposed by heat, while
rubidium nitrate will decompose to
form rubidium nitrite and oxygen.
| 2RbNO3
(s) _______ 2RbNO2 (s) + O2 (g)
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heat
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(iii)
Rubidium could be extracted from its
ore by the method of electrolysis.
Comment:
Electrolysis is the method used to
extract very reactive metals from
their ores. Rubidium is more reactive
than sodium, as it is below it in
the group and will ionise and lose
its electrons more readily.
(iv)
Rubidium will dissolve rapidly in
the water in a vigorous or explosive
reaction. Effervescence will also
be seen. The litmus changed from red
to blue as an alkaline solution was
now formed (RbOH).
Comment:
Reactive metals react with water to
form the hydroxide and to liberate
hydrogen.
QUESTION
2.
2.Calcium
[40Ca] and barium [137.36 Ba] are
in the same group of the periodic
table.
(a)
State the number of electrons in the
outer shell of the barium (Ba) atom.
(b)
Would you expect barium to be a metal
or non-metal?
(c)
Which of these elements would be more
reactive?
(d)
The mass number of barium is not a
whole number. Explain how this is
possible.
(e)
Write the formula for barium carbonate.
(f)
(i) Write a balanced equation for
the reaction between barium carbonate
and dilute sulphuric acid. Suggest
a reason why this reaction would be
unsuitable for the laboratory preparation
of carbon dioxide.
ANSWERS
2.
(a) Barium has two electrons in its
outer shell.
Comment:
Calcium has two electrons in its outer
shell (2:8:8:2) and since barium is
in the same group, it will also have
two outer
electrons.
(b)
Barium is expected to be a metal.
(c)
Barium would be more reactive as it
is below calcium in the group. Its
outer electrons are farther away from
the nucleus and will be lost more
readily.
Remember:
the reactivity of a metal is based
on how readily it gives up its outer
electrons.
(d)
An element generally has atoms of
different masses or isotopes making
it up. These
isotopes occur in different relative
proportions and when the contribution
of each isotope is added up, the mass
number may or may not be a whole number.
For
example neon consists of 90.92 per
cent of neon-20, 0.26 per cent of
neon-21 and 8.82 per cent of neon-22.
When the atomic mass of neon is calculated
it is 20.2 (not a whole number).
(e)
Barium carbonate - BaCO3 (Ba2+ ions
and CO32- ions).
(f)
BaCO3 (s) + H2SO4 (aq) == BaSO4 (s)
+ CO2 (g) + H2O (l)
This
reaction is unsuitable for preparing
carbon dioxide because, as soon as
the reaction starts, insoluble barium
sulphate would be formed which would
hinder the progress of the reaction.
*
Francine Taylor-Campbell is
an independent contributor.
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