Reactions of Metals
IJSO Training (Phase 3)
Dr. Kendrew K. W. Mak
Department of Chemistry
The Chinese University of Hong Kong
1
Structure and Bonding (鍵合) in
Metals
Metal atoms are bonded to one another in a Giant Metallic Structure (巨
型金屬結構) by Metallic Bonds (金屬鍵), which result from the attraction
between a “sea” of delocalized electrons (離域電子) and metal ions.
2
Conduction of Electricity by
Metals
The delocalized electrons move
towards the positive pole (正極)
of the battery, leaving the metal.
At the same time, an equal
number of electrons move into
the other end of the metal from
the negative pole (負極).
3
Properties of Metals Explained
by Structure and Bonding
•
Good conductors of electricity and heat – electrons are delocalized
•
Solids with high melting points (熔點) and boiling points (沸點) –
•
Have high densities (密度) – close packing of atoms
•
Malleable (can be rolled into sheets) and ductile (can be pulled
out into wire) – metal atoms are held together by the non-
strong giant lattice structure (巨型晶格結構)
directional metallic bonds
4
Comparing Reactivity (活潑性)
of Common Metals
How to compare:
1. The lowest temperature at which the reaction can be initiated.
2. The rate of reaction.
3. The amount of heat energy given out from the reaction.
For a fair comparison of reactivity:
1. Should be allowed to react with the same substance
2. Should be roughly in the same state of subdivision (e.g. all
in large lumps or all in fine powder)
3. Should react under the same conditions of temperature
and pressure.
5
Reactions of Metals with Air
Different metals react with air at very different rates. Reactive metals like
potassium (鉀) burn vigorously in air with characteristic flame and form
metal oxides by combining with oxygen and form metal oxides. Some less
reactive metals do not burn in air. They only react moderately even when
are heated strongly. Some metals are very inert (惰性) and do not react
with air/oxygen at all even under very strong heating. The trend of
reactivity gives the Metal Reactivity Series (金屬活性序).
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Reactions of Metals with Air
Potassium 鉀 (K)
Sodium 鈉 (Na)
Calcium 鈣 (Ca)
They are ignited easily by gentle heating. They burn
vigorously and give metal oxides (金屬氧化物).
Strong heating is required to ignite the metal. It burns
vigorously.
Magnesium 鎂(Mg) Strong heating is required to ignite the metals. They burn
with dazzling (耀眼) white flame.
Aluminium 鋁 (Al)
Zinc 鋅 (Zn)
It burns moderately under strong heating.
Iron 鐵 (Fe)
It does not burn but gives showery sparks under strong
heating.
Lead 鉛 (Pb)
They do not burn in air. They oxidize into oxides (氧化物)
under strong heating.
Copper 銅 (Cu)
Mercury 汞 (Hg)
It does not burn in air but oxidizes under heating. Strong
heating can decompose the metal oxide back into the metal.
Silver 銀 (Ag)
They do not react with air under strong heating.
Gold 金 (Au)
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Reactions of Metals with Air
Burn in Air:
Potassium 鉀 (K)
Sodium 鈉 (Na)
Calcium 鈣 (Ca)
Magnesium 鎂 (Mg)
Aluminium 鋁 (Al)
Zinc 鋅 (Zn)
Iron 鐵 (Fe)
4 K(s) + O2(g)  2 K2O(s)
4 Na(s) + O2(g)  2 Na2O(s)
2 Ca(s) + O2(g)  2 CaO(s)
2 Mg(s) + O2(g)  2 MgO(s)
4 Al(s) + 3 O2(g)  2 Al2O3(s)
2 Zn(s) + O2(g)  2 ZnO(s)
3 Fe(s) + 2 O2(g)  Fe3O4(s)
No Not Burn:
Lead 鉛 (Pb)
Copper 銅 (Cu)
Mercury 汞 (Hg)
2 Pb(s) + O2(g)  2 PbO(s)
2 Cu(s) + O2(g)  2 CuO(s)
2 Hg(s) + O2(g)  2 HgO(s)
No Reaction:
Silver 銀 (Ag)
Gold 金 (Au)
8
Appearance of Metals and
Storage Methods
The shiny surface of very reactive metals (potassium, sodium) soon becomes
dull when exposed to air.
The metal reacts with the oxygen in air to give the metal oxide.
Sodium and potassium are often protected from oxygen and moisture by
storing under paraffin oil (石蠟油).
Calcium are usually stored in airtight containers.
9
Reactions of Metals with Water
Alkali metals (鹼金屬) are so reactive that they react vigorously and
exothermically (放熱) with water. In some cases the heat generated is
sufficient to ignite the metal. In general the reactions of metals with
water produce hydrogen gas (H2) and the hydroxides (氫氧化物) of the
metals. Metals with moderate to low reactivity react very slowly with
water. However, they react moderately with steam when heated and give
hydrogen gas and metal oxides. Metals low in the metal reactivity series
do not react with water even at high temperature.
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Reactions of Metals with Water
Metal
Reactivity (活潑性)
Potassium (K) They react vigorously with cold water. The heat generated
from the reaction can ignite the metals.
Sodium (Na)
Calcium (Ca)
It reacts slowly with cold water.
Magnesium
(Mg)
It reacts very slowly with hot water. It reacts with steam when
being heated and gives hydrogen gas and metal oxide.
Aluminium (Al) They do not react with cold or hot water. They react with
steam when being heated and give hydrogen gas and metal
oxides.
Zinc (Zn)
(Iron oxidizes to hydrated iron oxide (水合氧化鐵) (rust) when
Iron (Fe)
oxygen is present in the water.)
Lead (Pb)
They do not react with water or steam.
Copper (Cu)
Mercury (Hg)
Silver (Ag)
Gold (Au)
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Actions of Potassium, Sodium
and Calcium on Water
Action of potassium on water
Potassium melts to a silvery ball, moves quickly on the water surface
with a hissing sound, and burns with a lilac (淡紫色) flame.
Potassium + Water  Potassium hydroxide solution (氫氧化鉀溶液) + Hydrogen gas
The resulting alkaline solution will turn red litmus (石蕊試紙) blue because of
the potassium hydroxide formed.
Action of sodium on water
The reaction of sodium with water is similar to that of potassium, except it is
less vigorous.
Sodium + Water  Sodium hydroxide solution (氫氧化鈉溶液) + Hydrogen gas
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Actions of Potassium, Sodium
and Calcium on Water
Action of calcium on water
Calcium reacts moderately with water, forming hydrogen gas and the slightly
soluble calcium hydroxide (氫氧化鈣) (milky suspension).
Calcium + Water  Calcium hydroxide + Hydrogen gas
13
Actions of Magnesium, Aluminium,
Zinc and Iron on Water
Action of magnesium on water
Magnesium has almost no reaction with cold water. It reacts slowly
with hot water to give the slightly soluble magnesium hydroxide (氫氧
化鎂) and hydrogen.
Magnesium + Water  Magnesium hydroxide + Hydrogen gas
Action of magnesium on steam
Magnesium reacts with steam vigorously when heated, and produce an
intense white light
Magnesium + Steam  Magnesium oxide (氧化鎂) + Hydrogen gas
14
Actions of Magnesium, Aluminium,
Zinc and Iron on Water
Action of zinc and iron on water/steam
Zinc and iron do not react with cold or hot water. They react with
steam slowly to give the respective oxides
Zinc + Steam  Zinc oxide (氧化鋅) + Hydrogen gas
Iron + Steam  Iron(II)iron(III) oxide (氧化鐵(III)鐵(II)) + Hydrogen gas
Action of aluminium on steam
Aluminium apparently does not react with steam. It is because
aluminium metal is usually coated with a very inert protective layer
of Al2O3.
15
Reactions of Metals with Dilute
Hydrochloric Acid(稀氫氯酸)
Metal
Reactivity
Potassium (K)
They react explosively with dilute hydrochloric acid.
Sodium (Na)
Calcium (Ca)
It reacts readily with dilute hydrochloric acid.
Magnesium
(Mg)
It reacts moderately with dilute hydrochloric acid.
Aluminium (Al) They react slowly with dilute hydrochloric acid.
Zinc (Zn)
Iron (Fe)
Lead (Pb)
It reacts very slowly with dilute hydrochloric acid.
Copper (Cu)
They do not react with dilute hydrochloric acid.
Mercury (Hg)
Silver (Ag)
Gold (Au)
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The Metal Reactivity Series
(金屬活性序)
By comparing their reactions with air, water and dilute hydrochloric acid,
we can arrange common metals in order of reactivity.
Potassium, K
Sodium, Na
Calcium, Ca
Magnesium, Al
Zinc, Zn
Iron, Fe
Lead, Pb
Copper, Cu
Mercury, Hg
Silver, Ag
Gold, Au
Most reactive
No reaction
with water/steam
Least reactive
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Applications of the Reactivity
Series
Reduction of Metal Oxides
A metal lower in the reactivity series has compounds with lower
stability (穩定性), so its oxide can be more easily reduced (還原).
1. Heating the metal oxide alone.
2 HgO(s)  2 Hg(l) + O2(g)
2 Ag2O(s)  4 Ag(s) + O2(g)
2. Reducing the metal oxide by another metal.
CuO(s) + Mg(s)  Cu(s) + MgO(s)
Fe2O3(s) + 2 Al(s)  2 Fe(s) + Al2O3(s) + heat
3. Reducing the metal oxide by carbon.
2 PbO(s) + C(s)  2 Pb(s) + CO2(g)
2 CuO(s) + C(s)  2 Cu(s) + CO2(g)
18