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12.


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Where are the alkali metals?
The elements in group 1, on the left of the periodic table, are called the alkali metals. lithium

Li
Na K Rb Cs Fr

sodium
potassium rubidium caesium francium

These metals are all very reactive and are rarely found in nature in their elemental form.
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What are the alkali metals?

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Why are they called the ‘alkali metals’?
The alkali metals are so reactive that, as elements, they have to be stored in oil. This stops them reacting with oxygen in the air. The alkali metals are unlike most other metals, which are usually hard and dense.

Alkali metals are soft enough to be cut with a knife, and the most common alkali metals, lithium, sodium and potassium, all float on water.
The elements in group 1 also react with water and form alkaline compounds. This is why they are called alkali metals.
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What is the electron structure of alkali metals? The alkali metals all have one electron in their outer shell. This means that: ? They are found in group 1 of the periodic table. ? They have similar physical and chemical properties. lithium 2,1

sodium 2,8,1

? They can readily lose the outer shell electron to form positive ions with a +1 charge and a full outer shell.

potassium 2,8,8,1

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How do you identify alkali metals?

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What are the properties of the alkali metals? The characteristic properties of the alkali metals are: ? They are soft and can be cut by a knife. Softness increases going down the group. ? They have a low density. Lithium, sodium and potassium float on water. ? They have low melting and boiling points.

These properties mean that the alkali metals are different to typical metals. However, alkali metals do also share some properties with typical metals: ? They are good conductors of heat and electricity. ? They are shiny. This is only seen when alkali metals are freshly cut.
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What is the trend in density?
The alkali metals generally become more dense going down the group, but the trend is not perfect because potassium is less dense than sodium. Element Density (g/dm3)

lithium
sodium potassium rubidium caesium Water has a density of 1 g/dm3.

0.53
0.97 0.86 1.53 1.87

Which elements in group 1 will float on water?
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What are the trends in density?

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What is the trend in melting and boiling point? The melting points and boiling points of alkali metals decrease going down the group.

Element
lithium sodium potassium rubidium caesium

Melting point (°C) 181
98 64 39 28

Boiling point (°C) 1342 883

760
686 671

The melting and boiling points decrease going down group 1 because the atoms get larger. In each metallic structure, the attraction between the positive metal ions and the delocalized sea of electrons gets weaker and so they become easier to melt, and to boil.
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What are the trends in melting point?

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What are the trends in boiling point?

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Properties of alkali metals quiz

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How do the alkali metals react with oxygen? All alkali metals react with oxygen in the air to form metal oxides. This produces a layer of dull oxide on the surface of the metal, called tarnish. The speed with which alkali metals react with oxygen in the air increases going down the group: ? lithium – tarnishes slowly ? sodium – tarnishes quickly ? potassium – tarnishes very quickly. Why are alkali metals stored in oil? The oil prevents them from reacting with oxygen and tarnishing.
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What is the equation for the reaction with oxygen? The reaction between an alkali metal and oxygen is an example of an oxidation reaction: alkali metal

+

oxygen ? alkali metal oxide

The word and chemical equations for the reaction between lithium and oxygen are: lithium 4Li (s)

+ +

oxygen ? lithium oxide O2 (g) ? 2Li2O (s)

What are the word and chemical equations for the reaction that causes sodium to tarnish?
sodium

+ 4Na (s) +

oxygen ? sodium oxide

O2 (g)

?

2Na2O (s)
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How do the alkali metals react with water?

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What does the reaction with water produce? All the alkali metals react vigorously with water. The reaction with water becomes more vigorous as you go down the group. It is an exothermic reaction as it releases a lot of heat. The reaction produces a gas that ignites a lighted splint with a squeaky pop. What is this gas? When green universal indicator is added to the reaction mixture, it turns purple. What does this tell you about the products of this reaction?

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What is the equation for the reaction with water? This reaction creates alkaline hydroxide ions. This is why the group 1 elements are called the alkali metals.

The general equation for the reaction between an alkali metal reacting with water is: alkali metal + water ? alkali metal + hydrogen hydroxide 2MOH (aq) + H2(g)

2M(s)

+ 2H2O(l) ?

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How does lithium react with water?
Lithium is the least reactive of the alkali metals. When added to water, it fizzes and moves around slowly across the surface of the water. What is the equation for this reaction? lithium 2Li (s)

+ +

water

?

lithium hydroxide 2LiOH (aq)

+ +

hydrogen H2 (g)

2H2O (l) ?

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How does sodium react with water?
When added to water, sodium fizzes more than lithium, and moves quickly across the surface of the water. The sodium melts as it reacts, and it becomes spherical and shiny, like a ball bearing. The hydrogen sometimes catches fire because of the heat from the reaction. What is the equation for this reaction? sodium

+

water

?

sodium hydroxide

+

hydrogen

2Na (s)
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+ 2H2O (l) ?

2NaOH (aq)

+

H2 (g)
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How does potassium react with water?
When added to water, the potassium moves across the surface of the water very quickly. The reaction produces so much heat that the hydrogen given off catches alight. What colour would the flame be? Like sodium, it melts with the heat of the reaction.

What is the equation for this reaction?
potassium 2K (s)
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+ +

water ? potassium hydroxide 2H2O (l) ? 2KOH (aq)

+ +

hydrogen H2 (g)
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How do alkali metals react with water?
Which of the alkali metals will react most strongly with water?

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How does electron structure affect reactivity?
The reactivity of alkali metals increases going down the group. What is the reason for this? increase in reactivity Li ? The atoms of each element get larger going down the group. ? This means that the outer shell electron gets further away from the nucleus and is shielded by more electron shells.

Na

? The further an electron is from the positive nucleus, the easier it can be lost in reactions. K ? This is why the reactivity of the alkali metals increases going down group 1.
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What is the order of reactivity?

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How do alkali metals react with chlorine?
Alkali metals burst into flames when heated and added to chlorine. They form metal chlorides. alkali metal

+

chlorine ? alkali metal chloride

The word and chemical equations for the reaction between lithium and chlorine are:

lithium
2Li (s)

+ chlorine ? lithium chloride
+
Cl2 (g) ? 2LiCl (s)

What are the word and chemical equations for the reaction that produces sodium chloride? sodium 2Na (s)
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+ +

chlorine ? sodium chloride Cl2 (g) ? 2NaCl (s)
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True or false?

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What are the uses of alkali metals?
How many uses of alkali metals can you see below?

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What are the uses of alkali metals?

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What are the uses of alkali metals?

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Glossary ? alkali metal – An element that belongs to group 1 of the
periodic table.

? exothermic – A reaction that releases heat into its
surroundings.

? metal chloride – The type of solid produced when an
alkali metal is burned in chlorine gas. ? metal hydroxide – The type of alkali produced by the reaction between an alkali metal and water.

? metal oxide – The type of solid produced when an alkali
metal reacts with oxygen. ? oxidation – The process by which a substance reacts and combines with oxygen.

? tarnish – The discolouration of metal after exposure to air
caused by the formation of an oxide on the metal’s surface.
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Anagrams

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Completing alkali metal equations

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Comparing reactivity with water

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Multiple-choice quiz

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