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Alkaline Earth Metals


The alkali earth metals are the elements in group 2 (II A) from periods 2 to 7 in the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). Alkali earth metals are not found as free elements in nature but rather in compounds of minerals and ores.

The substance that acted in ways similar to potash and soda (alkaline caustics) were classed as alkali earth metals. The alkaline earth metals resemble the alkali metals in many of their properties. The oxides of alkaline earth metals are alkaline and they occur in the earth crust. The last element radium was discovered in the ore pitchblende by Madam Curie.

Alkaline Earth Metals Definition

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"The alkaline earth metals are the elements of group II A on the periodic table". They are less reactive than the alkali metals, but they too do not exist free as pure metals in nature.

Alkali earth metals include Be, Mg and Ra. The metals of this family are harder, more dense and higher melting than the corresponding members of the group of alkali metals. Alkali metal atoms are more strongly bonded in the solid state than the alkali metals. The trends in properties dependent on bonding between atoms show a decrease in strength of bonding with increasing atomic radius as is true for alkali metals.

Alkaline Earth Metals List

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Alkaline earth metals are located on the left edge of the periodic table in the second columns. Alkaline earth metals are chemically quite active and are not found in pure elemental form on earth. Comprising the adjoining column of the periodic table are the following alkaline earth metals are
  1. Beryllium (Be)
  2. Magnesium (Mg)
  3. Calcium (Ca)
  4. Strontium (Sr)
  5. Barium (Ba)
  6. Radium (Ra)

Alkaline earth metals are not as reactive as alkali metals. Alkali earth metals do not burn at room temperature.They are less volatile, denser and not as soft as the alkali metals.

Periodic Table Alkaline Earth Metals

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The alkaline earth metals are found in Group 2 of the periodic table. Elements of this group are soft, highly reactive metals. They are most useful to humans in compounds with other elements.

The alkaline earth metals contain beryllium, magnesium, calcium, strontium, barium and radium. the group lies in the s-block of the periodic table shown below.

Periodic Table Alkaline Earth Metals

All the compounds of alkali and alkaline earth metals are colorless. The alkali earth metals are harder than the alkali metals, but still soft compared to many other metals.

Alkaline Earth Metals Group

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Group 2 elements beginning with Beryllium (Be) and running vertically to Radium (Ra) are called alkaline earth metals. The alkali earth metals (Group 2A) - beryllium, magnesium, calcium, strontium, barium and radium - have the valence electron configuration ns2.

Group 2 elements have outermost s electrons. These s electrons are situated much further from the nucleus than all other electrons in the metals, so they are only weakly held by the positive nucleus. The alkaline earth metals family are given below.

Alkaline earth metals
1 Beryllium Be
Magnesium Mg
Calcium Ca

Alkali and Alkaline Earth Metals

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The alkali metals and alkaline earth metals are members of Group I and II respectively in the periodic table. The alkali earth metals are not as reactive as the metals to their left on the periodic table.

Furthermore, the alkali metals have a combining power of one; the alkaline earth metals have a combining power of two. This means that when an alkali metal atom reacts with one other atom such as chlorine an alkaline earth atom will react with two of those atoms.

Alkali and Alkaline Earth Metals

Still the two groups share some characteristics. Being highly reactive they are not found as elements in nature but as compounds. Also the elements in both groups are powerful reducers meaning they are able to force electrons into other compounds.

Alkaline Earth Metals Properties

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Like other groups the members of this family show specific patterns in their electron configuration. The alkaline earth metals provide a good example of group trends in chemical properties within the periodic table.

Physical Properties of Alkaline Earth Metals

  1. Atomic and ionic radii - The atomic and ionic radii of alkaline earth metals are fairly large but are smaller than the corresponding members of the alkali metals.
  2. Ionization enthalpy - The alkali metals have low ionization energies due to large size of the atoms.
  3. Metallic character - The alkaline earth metals are highly electropositive and have a strong tendency to lose both the valence electrons.
  4. Melting and boiling point - Alkaline earth metals have low melting and boiling points but these are higher than those of the corresponding alkali metals.
  5. Oxidation state - Alkaline earth metals consistently exhibits +2 oxidation state in their compounds.
  6. Flame colorization - Like alkali metals except Be and Mg all all other alkaline earth metals also impart characteristic colors to the flame.
Magnesium Calcium
- -
Brick red
Crimson red
Apple green
Crimson red

Chemical Properties of Alkaline Earth Metals

Electrode potential and reactivity - All alkaline metals have a strong tendency to release two valence electrons and change into bivalent cations having inert gas electronic configuration.

M $\leftrightharpoons$ M2+ + 2e-

Reaction with water - Since alkali earth metals are less electropositive they slowly react with water liberating hydrogen and forming metal hydroxides. For example, the reaction of magnesium with water is

Mg + 2H2O $\rightarrow$ Mg(OH)2 + H2

Reaction with air - The alkaline earth metals being electropositive than the alkali metals are less reactive. They are slowly oxidized on exposure to air.However they burn in oxygen to form ionic oxides.

Reaction with nitrogen - All the alkali metals react with nitrogen to form their respective nitrides.

3M + N2 $\overset{H_{2}O}{\rightarrow}$ M3N2

Reaction with hydrogen - All the alkali metals except beryllium directly combines with hydrogen on heating to form hydride. (MH2)

Reaction with halogens - All alkali earth metals combine with halogens at elevated temperatures forming MX2.

M + X2 $\rightarrow$ MX2

Reaction with ammonia - Like alkali metals all alkali earth metals dissolve in liquid ammonia to give deep blue solutions due to ammoniated electrons.

Reaction with acids - Alkaline earth metals react with acids liberating hydrogen.

M + 2HCl $\rightarrow$ MCl2 + H2

Tendency to form complex - Alkaline earth metals have a tendency to form some stable complexes with organic and inorganic ligands.

Formation of amalgam and alloy - All the alkaline earth metals forms amalgam with mercury and alloys with other metals.

Uses of Alkaline Earth Metals

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  1. The plaster of paris (CaSO4.$\frac{1}{2}$H2O) is an important compound and it is largely used in surgery for setting fractured bones.
  2. A suspension of Mg(OH)2 in water is used in medicine as an antacid under the name of milk of magnesia.
  3. The suspension of slaked lime in water is known an white wash which is used in white washing of buildings.
  4. The finely divided BaSO4 is used in paints and it is called Blanc fire.
  5. Gypsum is used for manufacture of cement, glazing paper and for making soil fertile.
  6. CaC2O4.2H2O is insoluble in bases but soluble in strong acids. This is a component of kidney stones.

Characteristics of Alkaline Earth Metals

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Characteristics of alkaline earth metals include
  1. Beryllium is the lightest of the alkali earth metals. It is extracted from the minerals beryl and chrysoberyl. Beryllium is a poison and may be carcinogenic.
  2. Magnesium is extracted from seawater. It burns with a very bright light when ignited in air. It is essential element for humans and is used in laxatives, Epson salts and dyes.
  3. Calcium is another essential element for humans. It is used in the manufacture of rare earth metals, zirconium, thorium and uranium. It is also used in drying agents and cement.
  4. Strontium is found in the minerals celestite and strontianite. It produces red coloring n flares and fireworks. It is also used in the manufacturing of television special glasses.
  5. Barium is extracted from the mineral barite. It is used in drilling fluids, paint pigments and for body imaging. Patients drink barium sulfate so doctors can see their gastrointestinal tracks with the help of x-ray machines.
  6. Radium is the heaviest of the alkaline earth metals and is the only radioactive member of the family. It was used as a luminous paint for which dials and to treat cancer.

Reactivity of Alkaline Earth Metals

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Alkaline earth metals are highly reactive due to their low ionization potential. None of them is found in free state in the nature. The chemical reactivity of alkaline earth elements is lesser than that of alkali metals. The reactivity of the alkaline earth metals (Group 2A) increases down the group, a trend that follows the decrease in ionization energies.

The trend in the reactivity of alkaline earth metals in the periodic table is shown below.

Reactivity of Alkaline Earth Metals

Examples of Alkaline Earth Metals

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The alkali metals are placed in group II A / group 2 that is the second group from the extreme left of the modern periodic table.
The examples of alkaline earth metals are
  1. Calcium (Ca)
  2. Barium (Ba)
  3. Beryllium (Be)
  4. Magnesium (Mg)
  5. Strontium (Sr)
  6. Radium (Ra)