Group 2 – The Alkaline Earth Metals 2

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1/4/2019
Group 2 – The Alkaline Earth Metals
Group 2 – The Alkaline Earth Metals
Introduction
The 'neighbours' of the alkali metals are the alkaline earth metals in Group 2 of the
Periodic Table. They are similar in many ways to the Group 1 metals but are not quite
as reactive as the corresponding element 'next door'. In this unit you can compare the
two groups of metals.
You might have used two of the elements, magnesium and calcium, in experiments.
You will certainly be familiar with many of their compounds, such as calcium carbonate
in limestone and chalk. These two elements are common in rocks, hence the word
'earth' in the Group 2 name.
Properties of the Group 2 elements
The elements in Group 2 of the Periodic Table are:
Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)
Strontium (Sr)
Barium (Ba)
Look at the first three of these elements below:
Figure 1. Beryllium. Figure 2. Magnesium. Figure 3. Calcium.
Unlike the Group 1 metals, these elements are not usually stored under oil.
What does the fact that the elements above are not stored in oil suggest to
you?
That Group 2 metals are not used in machinery
That Group 2 metals are less reactive than group 1 metals
That Group 2 metals are more reactive than group 1 metals
Fig.4 shows a piece of barium, which is near the bottom of Group 2.
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Group 2 – The Alkaline Earth Metals
Figure 4. Barium.
Is the piece of barium as shiny as the other Group 2 metals shown earlier?
What does this suggest to you?
Group 2 metals get less reactive as we go down the group.
Group 2 metals get more reactive as we go down the group.
The alkaline earth metals have low melting points and low densities for metals.
However, the values for a particular alkaline earth metal are higher than for the
neighbouring metal in Group 1. Like all metals they are good conductors of heat and
electricity.
The general trend in the melting points of the Group 2 metals is the same as
that in Group 1. Put the following metals in order of their melting points (highest
first):
Sodium
Beryllium
Magnesium
Reactions of the alkaline earth metals
The atoms of the Group 2 elements all have 2 electrons in their highest energy level
(outermost shell). They lose these 2 outer electrons when reacting to form ionic
compounds.
What is the electronic structure of a calcium atom? (The atomic number of
calcium is 20.)
2, 8, 10
2, 8, 2, 8
2, 8, 8, 2
2, 2, 8, 8
What will be the charge on an ion of an alkaline earth metal?
2−
2+
Try adding magnesium and calcium to water in this simulation:
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Group 2 – The Alkaline Earth Metals
Figure 5. Group 2 metals reacting with water.
Magnesium reacts only very slowly with water (it takes a few days to collect a test tube
of the hydrogen gas given off), whereas calcium fizzes straight away. Hydrogen gas is
given off and an alkaline solution is formed, as described by the following equation:
calcium + water calcium hydroxide + hydrogen
Ca(s) + 2 H2O(l) Ca(OH)2(aq) + H2(g)
The solution left after calcium reacts with water is alkaline because it contains
…
hydrogen gas.
hydroxide ions.
hydrogen ions.
Strontium gives off hydrogen more quickly than calcium, and barium's reaction with
water is quicker still. This shows that:
Group 2 metals get more reactive as we go down the group.
Which of the following equations correctly describes the reaction of strontium
with water?
Sr(s) + 2 H2O(l) Sr(OH)2(aq) + H2(g)
2 Sr(s) + 2 H2O(l) 2 SrOH(aq) + H2(g)
Which of the following equations correctly describes the reaction of barium with
water?
2 Ba(s) + 2 H2O(l) Ba(s) + 2 H2O(l) 2 Ba(OH)2(aq) + H2(g)
Ba(OH)2(aq) + H2(g)
Because each Group 2 metal is less reactive than its neighbour in Group 1, we can
safely add some of them to dilute acid. For example, look at the reactions of
magnesium and calcium with dilute hydrochloric acid:
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Group 2 – The Alkaline Earth Metals
Figure 6. Magnesium and calcium reacting with dilute hydrochloric acid.
The equation for the reaction with magnesium is:
magnesium + hydrochloric acid magnesium chloride + hydrogen
Mg(s) + 2 HCl(aq) MgCl2(aq) + H2(g)
Decide whether the following statements are true or false.
Magnesium reacts more quickly with dilute
acid than calcium.
Calcium reacts more quickly with dilute acid
than magnesium.
There is no difference in the reactivity of
magnesium and calcium with dilute acid.
Both magnesium and calcium give off
oxygen gas when they react with dilute acid.
Both magnesium and calcium give off
hydrogen gas when they react with dilute
acid.
Which of the following shows the balanced equation for magnesium reacting
with dilute sulfuric acid?
Mg(s) + HSO2(aq) Mg(s) + 2 HNO3(aq) Mg(s) + HSO4(aq) MgSO2(aq) + H2(g)
Mg(NO3)2(aq) + H2(g)
MgSO4(aq) + H2(g)
Uses of the Group 2 elements and their compounds
Magnesium burns with a bright white flame and this has led to its use in fireworks and
rescue flares. A more surprising use of the metal is in the manufacture of high
performance car engines. For example, the Volkswagen 'Beetle' has a magnesium
crankcase and other engine parts, and the Porsche 911 contains more than 50 kg of
magnesium. It is used because of its low density, thereby reducing fuel consuption and
reducing pollution from cars. Magnesium compounds also have their uses. For
example:
Magnesium hydroxide is the acive ingredient in some indigestion remedies. It
neutralizes the excess acid that causes heartburn.
Magnesium oxide has a very high melting point so it is used as a lining inside
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Magnesium sulfate is found in Epsom salts, a laxative.
Strontium compounds are used in fireworks to produce a crimson red colour.
Barium compounds are very poisonous and barium carbonate is used as a rat poison.
However, you might have heard of 'barium meals' in hospitals, where patients swallow
a white substance which shows up their digestive tract when X­rayed. This contains
barium sulfate, which is insoluble in water and so just passes through your body
without doing any harm.
Figure 7. X­ray following a 'barium meal'.
The uses of common calcium compounds, such as calcium carbonate and calcium
hydroxide are covered in the chapter, Limestone.
Summary
The alkaline earth metals from Group 2 of the Periodic Table are reactive metals.
However, each Group 2 metal is less reactive than the neighbouring element in Group
1.
Like the Group 1 metals, they get more reactive as we go further down the group.
Exercises
1. What do we call the elements in Group 2 of the Periodic Table?
Alkali metals
Alkaline earth metals
Transition metals
2. Which Group 2 element is the most reactive?
Beryllium
Magnesium
Calcium
Strontium
Barium
3. Sodium and magnesium lie next to each other in Groups 1 and 2 of the
Periodic Table respectively. Which element has the higher melting point?
Sodium
Magnesium
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4. Which element has the higher density?
Sodium
Magnesium
5. Which gas is given off when calcium reacts with water?
Oxygen
Carbon dioxide
Hydrogen
6. Name the product that forms in solution when calcium reacts with water.
Calcium chloride
Calcium hydride
Calcium hydroxide
7. What will be the pH value of the solution formed when calcium reacts with
water?
1
3
7
10
8. What is the formula of barium hydroxide?
BaOH
Ba(OH)2
BaH2
Ba(H2O)2
9. Decide whether the following substances are products of the reaction
between calcium and dilute hydrochloric acid.
Hydrogen
Chlorine
Oxygen
Calcium oxide
Calcium hydroxide
Calcium chloride
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