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S and P-Block Elements >>
Occurrence and uses of Alkaline Earth Metals
Occurrence and uses of alkaline earth metals
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Elements
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Abundance
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Main Minerals |
Uses
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Beryllium
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2.8 ´ 10-3%
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First detected in 1798 in the gemstone beryl and emerald (Be2Al2Si6O18)
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Used in corrosion resistant alloys.
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Magnesium
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2.33%,
7th most abundant element in earth’s crust
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Pure Mg first prepared in 1800, named after the magnesia district in Thessaly Greece where large deposits of the mineral are found
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When alloyed with Al, Mg is widely used as structural materials because of its high strength, low density and ease in machining.
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Calcium
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4.15%, 5thmost abundant element in earth’s crust.
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CaCO3.2H2O obtained in pure form in 1808, calcium is derived from latin word calx, meaning “lime”
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As an alloying agent for hardness in aluminium compounds. Calcium is the primary constituent of teeth and bones.
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Strontium
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0.038%
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Discovered in 1787 and named after the small town of strontion (Scotland)
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SrCO3 is used for the manufacture of glass for colour TV picture tubes.
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Barium
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0.042%
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Found in minerals witherite (BaCO3) and barite (BaSO4) after which it is named.
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BaSO4 is used in medicine as a contrast medium for stomach and intestine
X – rays
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Radium
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Traces
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Isolated as chloride in 1898 from the mineral pitchblende
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Used in cancer radiotheraphy
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Group IIA (Alkaline earth metals) and groups IIB (Zn, Cd, Hg) Mg acts as a bridge element between IIA and IIB.
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S.No.
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Properties
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IIA(Be, Mg, Ca, Sr, Ba, Ra)
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IIB (Zn, Cd, Hg)
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1
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Electronic configuration
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[Inert gas] ns2
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[Inert gas] (n – 1)d10ns2
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2.
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Block
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S – block
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d – block
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3.
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Oxidation state
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+2
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+2, mercury also forms dimeric Hg2+2
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4.
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Nature of oxide
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BeO is amphoteric, other oxides are basic.
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ZnO is amphoteric, CdO and MgO are basic
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5.
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Nature of Halides
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Electron – deficient BeX2, others (MX2) are ionic:
MgCl2 < CaCl2 < SrCl2 < BaCl2
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ZnCl2, CdCl2 are ionic but less than IIA, HgCl2 is covalent.
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6.
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Nature of sulphates
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Less soluble in water and solubility decreases down the group BeSO4 > MgSO4 > CaSO4 > SrSO4 > BaSO4
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More soluble than IIA
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7.
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Nature of hydroxides
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Solubility of hydroxides increases as we move down the group.
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Solubility of hydroxides decrease as we move down the group.
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8.
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Nature of sulphides
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Soluble
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ZnS, CdS, HgS insoluble and precipitate in salt analysis.
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9.
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Reactivity
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Increases as we move down the group Be < Mg < Ca < Sr < Ba
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Decreases as we move down the group Zn > Cd > Hg
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