The Alkali (Group 1) Metals |
Members of Group 1 |
There are six elements in Group 1 of the Periodic Table. In increasing reactivity; lithium, sodium, potassium, rubidium, cesium and francium (which is radioactive and highly unstable). Hydrogen although it appears at the top of group one is not included except for one rare circumstance; under extremely high pressure,
such as is found at the core of Jupiter, hydrogen does become metallic and behaves like an alkali metal.
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Properties |
The reactivity of group 1 metals increases from the top (lowest atomic number) to the bottom (highest atomic number) of the group, there are simlar trends to be observed with melting points and density. All members of Group 1 are very reactive, they are never found in elemental form in nature and they have to
be stored in oil to prevent them from reacting with oxygen or moisture in the air. When they react with water they produce alkaline solutions.
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These metals are all easily cut with a knife, they are all shiny, but because of the high reactivity quickly turn dull if
directly exposed to air as they oxidize easily. Compared to other metals the Group 1 Metals all have low melting points. Like
all other metals they are good conductors of electricity. They all have low densities compared to other metals and will float
on water.
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Reactions |
The alkali metals react readily with halogens to form ionic salts, and with water to form strongly alkaline (basic) hydroxides. These elements all have one electron in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose one electron to form a singly charged positive ion.
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Alkali metals are famous for their vigorous reactions with water, and these reactions become increasingly violent as you move
down the groups. The reaction with water is as follows:
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With potassium as an example; |
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When lithium is dropped into water it fizzes and turns into lithium hydroxide (LiOH). Like with all the alkali metal reactions with water, hydrogen gas is also released during this reaction with water.
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The reaction of sodium with water generates so much heat that it melts the sodium. It moves around on the surface of the water rapidly, and sparks are sometimes observed. This ignites the hydrogen gas which is released during this reaction. The resulting compound is sodium hydroxide (NaOH).
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The reaction of potassium with water is violent. Extreme precautions are needed, since the molten metal is often ejected from the surface of the water
into the air. In this reaction, enough energy is produced to ignite the hydrogen, creating a lilac flame above the potassium. The resulting compound is potassium hydroxide (KOH).
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The reaction of sodium with chlorine gas produces common table salt (NaCl), the reaction gives a bright yellow flame. This compound is colourless. Other salts are also produced in reactions with chlorine; lithium chloride (LiCl) and potassium chloride (KCl) are other salts.
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Uses |
Because they are so reactive the Group 1 metals have few practical applications. |