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Monday, May 30, 2011

Metals & Non Metals extrascore notes

Metals
Metals have certain characteristic physical properties: 
They are usually shiny (they have "lustre")
They have a high density, are ductile and malleable
They usually have a high melting point, 
They are usually hard, and conduct electricity and heat. 
These properties are mainly because each atom exerts only a loose hold on its outermost electrons (valence electrons); 
On the periodic table, a diagonal line drawn from boron (B) to polonium (Po) separates the metals from the nonmetals. 
Most metals are grayish in color, but bismuth is pinkish, copper is red, and gold is yellow. Some metals display more than one colour, a phenomenon called pleochroism.

Ores
An ore is a mineral containing a metal as a proportion of its content. Usually, it is used in the context of a mineral from which it is economical to extract its metallic component. Ores are mined.
Substance            Important Ores
Aluminium          Bauxite Al2O3
Antimony            Stibnite Sb2S3
Beryllium            Beryl , Crysoberyl
Calcium              Lime stone, Marble, Chalk, Gypsum, Alabaster , Flurosper
Chromium          Chromite (Feo Cr2 O3)
Cobalt                Smaltite
Copper              Cuprite (Cu2O), Bornite
Iron                    Hematite Fe2O3, Magnatite (Fe3O4)
Lead                  Galena (Pbs), Masicot, Serusite
Magnicium         Magnesite, Dolomite, Carnallite
Manganese         Pyrolusite, Hausmannite
Mercury             Cinnabar
Molybdenum      Molybdenite & wulfenite
Nickel                Pantilandite and Gargnierite
Phosphorous      Phosphorite Apatite, Chlorapatite
Potassium           Carnelite , Saltpetre (KNO3)
Silver                   Argentite(AgS2)
Sodium              Rock Salt( Nacl) Chile Saltpetre (NaNO3)
Sulphur            Galena, Copper Pyrites & Iron Pyrites
Some important processes employed for the metal extraction are:

a) Gravity separation: The crushed ore are suspended either in water or an air blast, the heavier metal or metallic mineral particles fall to the bottom of the processing chamber, and the lighter gangue is blown or washed away. Gold and magnetite are separated in this way .

b) Flotation: In this method, finely ground ore is mixed with a liquid. The metal or metallic mineral floats while the gangue sinks

c) Magnetic separation: Metals that have magnetic properties are concentrated by means of electromagnets that attract the metal but do not attract the gangue e.g. magnetite

d) Smelting: the ore is heated with a reducing agent and a flux to a high temperature. The reducing agent combines with the oxygen in a metallic oxide, leaving pure metal; and the flux combines with the gangue to form a slag that is liquid at the smelting temperature and thus can be skimmed off or poured away from the metal. The production of pig iron in blast furnaces is an example of smelting and the process is also used to extract copper, lead, nickel, and many other metals from their ores.

e) Amalgamation is a metallurgical process that utilizes mercury to dissolve silver or gold to form an amalgam. This process has been largely supplanted by the cyanide process, in which gold or silver is dissolved in solutions of sodium or potassium cyanide.
 f) Electrolysis: In this process, the metal is deposited at the cathode from aqueous solutions or in an electrolytic furnace. Copper, nickel, zinc, silver, and gold are several examples of metals that are refined by deposition from aqueous solutions. Aluminium, barium, calcium, magnesium, beryllium, potassium, and sodium are metals that are processed in electrolytic furnaces.
 Some interesting points
Osmium and iridium (specific gravity 22.6) are the most dense metals, and lithium (specific gravity 0.53) is the least dense. 
Bismuth has the lowest electrical conductivity of the metallic elements, and silver the highest at ordinary temperatures. 
Gallium, mercury, cesium, and rubidium are the only metal elements that melt near room temperature
Metalloids
A group of elements called metalloids, intermediate in properties between the metals and the nonmetals, are sometimes considered a separate class.
They have properties intermediate between those of metals and nonmetals. most common is that metalloids are usually semiconductors rather than conductors.
They are boron (B) silicon (Si) germanium (Ge) arsenic (As) antimony (Sb) tellurium (Te) Polonium (Po)
 Non metal
A non metal is a substance that conducts heat and electricity poorly, is brittle or waxy or gaseous, and cannot be hammered into sheets or drawn into wire. 
Non metals gain electrons easily to form anions . About 20% of the known chemical elements are non metals. The oxides of nonmetals are acidic.
The nonmetals are, in order of atomic number:
hydrogen (H) carbon (C) nitrogen (N) oxygen (O) fluorine (F) phosphorus (P) sulfur (S) chlorine (Cl) selenium (Se) bromine (Br) iodine (I) astatine (At)
Alkali metals
Alkali Metals, series of six chemical elements in group 1 (or Ia) of the periodic table They are soft compared to other metals, have low melting points, and are so reactive that they are never found in nature uncombined with other elements. They are powerful reducing agents. The alkali metals are, in order of increasing atomic number, lithium, sodium, potassium, rubidium, cesium, and francium. Francium exists only in a radioactive form.
Alkaline Earth Metals
It is a series of six chemical elements in group 2 (or IIa) of the periodic table. Although rather brittle, the alkaline earth metals are malleable, conduct electricity and when heated, burn readily in air. The alkaline earth metals are, in order of increasing atomic number, beryllium, magnesium, calcium, strontium, barium, and radium. Their oxides are called alkaline earths.
 Metals are Electropositive Elements
Metals are very reactive. Metals tend to loose electrons easily and form positively charged ions; therefore metals are called electropositive elements. Sodium metal forms sodium ions Na+, Mg forms positively charged Magnesium ions Mg2+and aluminium forms aluminium ions Al3+. The electropositive nature allows metals to form compounds with other elements easily.

Reaction of Metals with Oxygen
Metals like sodium (Na) and potassium (K) are some of the most reactive metals. Potassium, sodium, lithium, calcium and magnesium react with oxygen and burn in air.

Metals from aluminium to copper in the activity series of metals, react slowly when heated in air to form the metal oxides. Aluminium is the fastest and copper is the slowest of them.
Sodium metal reacts with the oxygen of the air at room temperature to form sodium oxide. Hence, sodium is stored under kerosene to prevent its reaction with oxygen, moisture and carbon dioxide.

Sodium oxide is a basic oxide which reacts with water to form sodium hydroxide.


Mg does not react with oxygen at room temperature. On heating, Mg burns in air with intense light and heat to form MgO.


Zinc metal burns in air only on strong heating to form zinc oxide.

Iron metal does not burn in dry air even on strong heating. In moist air, iron is oxidized to give rust.
 
On heating in air it burns with a brilliant flame forming triferric tetroxide.
 
Copper is the least reactive metal and does not burn in air even on heating. However, on prolonged strong heating copper reacts with oxygen and forms copper (II) oxide (CuO) outside and copper (I) oxide (Cu2O) inside.

Gold and platinum do not react with oxygen in air.
Reaction of Metals with Water
Potassium, sodium, lithium and calcium react with cold water.
Sodium reacts vigorously with cold water forming sodium hydroxide and hydrogen.

Metals from magnesium to iron in the activity series of metals, react with steam (but not H2O) to form the metal oxide and hydrogen gas.



Red hot iron reacts with steam to form Iron (II, III) oxide.


Note: The reaction between iron and steam is irreversible. Tin, lead, copper, silver, gold and platinum do not react with water or steam.
Reaction of Metals with Acids
Potassium, sodium, lithium and calcium react violently with dilute H2SO4 and dilute HCl, forming the metal salt (either sulphate or chloride) and hydrogen gas. The reaction is similar to the reaction with water.




Magnesium, aluminium, zinc, iron, tin and lead react safely with dilute acid. Magnesium is the fastest and lead is the slowest of the six.

Zinc with dilute sulphuric acid is often used for the laboratory preparation of hydrogen. The reaction is slow at room temperature, but its rate can be increased by the addition of a little copper (II) sulphate. Zinc displaces copper metal, which acts as a catalyst.

Metals below hydrogen (copper, silver, gold and platinum), will not react with dilute acid. They cannot displace hydrogen from the non-metal anion.

Note:  Copper reacts with oxyacids like nitric acid and sulphuric acid because these acids are strong oxidizing agents.
In general,
Hydrochloric acid makes a metal chloride.
Sulphuric acid makes a metal sulphate.
Reactions with nitric acid are more complex, the nitrate is formed but the gas is rarely hydrogen, and more often, an oxide of nitrogen.
Reaction of Metals with Salt Solutions
Reactive metals can displace any metal less reactive than itself, from the oxide, chloride or sulphate of the less reactive metal in solution or their molten state. 
If metal A displaces metal B from its solution, it is more reactive than B.

Copper (II) sulphate solution is blue; iron sulphate solution is almost colourless when dilute. During the displacement, the blue solution loses its colour and the iron metal is seen to turn pink-brown as the displaced copper becomes deposited on it.

On heating the mixture of magnesium powder and black copper (II) oxide, white magnesium oxide is formed with brown bits of copper:

Adding magnesium to blue copper (II) sulphate solution, the blue colour fades as colourless magnesium sulphate is formed and brown bits of copper metal form a precipitate
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