alkaline earth metals beryllium magnesium calcium strontium barium radium
TRANSCRIPT
Alkaline Earth MetalsBeryllium
Magnesium
Calcium
Strontium
Barium
Radium
• Why were these elements called “alkaline earth
metals”?
• What do you think about the uses of these elements
commonly?
Alkaline Earth Metals
• The word “earth” was used for the oxides of group 2A by the
ancient scientists.
• Alkaline earth metals, after the alkali metals, are secondary
metals with strong metallic properties.
• The group 2A elements are less active than those of 1A, but
more active than those of group 3A.
• Except Be, all form ionic compounds.
• Be forms mostly covalent compounds.
• The atomic radius increases from top to bottom.
•The melting point, boiling point and the hardness of the elements decrease from top to bottom.
• Beryllium is the hardest alkaline earth metal
• Barium is the softest alkaline earth metal.
• Malleable and ductile.
• Excess Mg+2 and Ca+2 in water means that it is hard.
Characteristic Flame Colors of Alkaline Earth Metals
BariumCalcium StrontiumMagnesium
Minerals of Some Alkaline Earth Metals
Chemical Properties
• They are Covered by their oxides when they are exposed to
air.
• Burn in air with bright flame.
•Activity of the metals increases from Be to Ba.
• Reactions of Ca, Sr and Ba are easy with water.
• Reactions of Be and Mg with water are difficult.
Chemical Properties
• Ca (s) + 2H2O(l) → Ca+2(aq) + 2OH-(aq) + H2(g)
• Mg (s) + 2H2O(l) → Mg(OH)2(s) + H2(g)
• 2Mg (s) + O2(g) → 2MgO(s)
• Mg (s) + H2(g) → MgH2(s)
• Ca (s) + 2HCI(aq) → CaCl2 + H2(g)
• Be (s) + 2HCI(aq) → BeCI2 + H2(g)
• All oxides and hydroxides of alkaline earth metals show basic properties.
• Oxides and its hydroxides of beryllium show amphoteric properties.
Compounds
• Ionic
• Have high melting and boiling points.
• Thermally stable.
• Less soluble in water than those of 1A metals.
• Solubility of salts increase from Be to Ba.
• Obtained by heating calcium
carbonate (limestone) at 900°C.
• CaCO3(s) → CaO(s) + CO2(g)
Calcium Oxide, CaO
Calcium Carbonate, CaCO3
• It forms by evolving CO2 gas from Ca(OH)2 solution.
• Small gray solid pieces
• Used widely in industry
• Prepared by the reaction of calcium oxide (lime) and coke.
CaO(s) + 3C(s) ↔ CaC2(s) + CO (g)
CaC2(s) + 2H2O(l) → C2H2(g) + Ca(OH)2(s)
Calcium Carbide, CaC2
CaSO4.2H2O : Gypsum
CaSO4.1/2H2O : Plaster of Paris
• Gypsum is a white substance and
used for fabrication into wallboard.
Calcium Sulfate, CaSO4
Uses
• Very light element
• To prepare some special alloys.
• 2% Be in Cu alloy in springs.
• Making glass for X-ray tubes.
• In the aerospace industry.
Beryllium
Uses
• Light metal
• Production of planes, missiles
• Some light household items.
• Flash in photography
Magnesium
• To increase the hardness, durability and
resistance to corrosion of alloys.
• Additive in rocket fuels and signal
rockets.
• Mg(OH)2 is used as a stomach antacid.
Magnesium
• Construction materials, bleaching agents.
• CaO in the production of some chemicals, steel, glass, paper
and sugar.
• CaC2 is used to produce acetylene gas
for welding.
• In fertilizers and
toothpaste
Calcium Compounds
• Ba is used as a gas absorbent in vacuum tubes.
• The alloys of Ba with Ni donate electrons so used in vacuum
tubes and in ignitors and spark plugs.
• Barium nitrate and barium chlorate are used to obtain green
light in fireworks.
Barium and Its Compounds
• BaSO4 is used to take the photos of stomach and intestines.
• Ba does not allow X-rays to pass like all elements with large
atomic number.
•The Ba+2 ion is toxic, but since the solubility of BaSO4 in
water is very low, its poisonous effect disappears.
Barium and Its Compounds
• The salts of strontium in signal rockets and fireworks to
produce red light.
• Nuclear batteries.
Strontium
• In self luminous paints and in radiotherapy.
• As a neutron source.
• On luminous watch dials.
Radium