Group 2 Metals

The alkaline earth metals, their properties and some of their uses

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2+ Ions

Beryllium, Be

  • Atom - 1s2 2s2
  • Ion - 1s2

Magnesium, Mg

  • Atom - 1s2 2s2 2p6 3s2
  • Ion - 1s2 2s2 2p6

Calcium, Ca

  • Atom - 1s2 2s2 2p6 3s2 3p6 4s2
  • Ion - 1s2 2s2 2p6 3s2 3p6

Group 2 elements have 2 electrons in their outer shells and lose these to form 2+ ions

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Reactivity of Group 2 Elements

As you go down the group ionisation energies decrease, due to:

  • increasing atomic radius
  • shielding effect

When Group 2 elements react they lose electrons to form positive ions

The easier to lose electrons, the more reactive the element

Reactivity increases down the group

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Group 2 Elements react with Water and Oxygen

When Group 2 elements react, the are oxidised from a state of 0 to +2

Group 2 metals react with water to give a metal hydroxide and hydrogen

M  +  2H2O   =   M(OH)2  +  H2

Oxidation numbers

0                        +2

Group 2 metals burn in oxygen to form solid white oxides

2M  +  O2   =   2MO

Oxidation numbers

0 +2

  0      -2

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Group 2 Oxides and Hydroxides

The oxides of the Group 2 metals react readily with water to form metal hydroxides, which dissolve. The hydroxide ions (OH-) make alkaline solutions

Magnesium oxide is an exception, it only reacts slowly and the hydroxide isn't very soluble

The oxides form more strongly alkaline solutions as you go down the group, because the hydroxides get more soluble

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Thermal Stability

Thermal decomposition is when a substance breaks down when heated. The more thermally stable a substance is, the more heat it will take to break it down

Group 2 carbonates decompose to form the oxide and carbon dioxide:

MCO3    =    MO  +  CO2

Thermal stability increases down the group

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Neutralising Acids

Group 2 elements are known as the alkaline earth metals, and many of their common compounds are used for neutralising acids

  • Calcium hydroxides is used in agriculture to neutralise acid soils
  • Magnesium hydroxide is used in some indigestion tablets as an antacid

Ionic equation:

H+   +   OH-    =   H2O

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