Physical Properties of Metals
Physical State
Metals are solids at room temp with the exception of mercury and gallium which are liquids at room temp.
Lustre
Metals have the quality of reflecting light from its surface and can be polished. Eg: Gold, silver and copper.
Malleability
Metals have the ability to withstand hammering and can be made into thin sheets called as foils.
Ductility
Metals can be drawn into wires. 100 gm of silver can be into a thin wire about 200 meters long.
Hardness
All metals are hard except sodium and potasium which are soft and can be cut with a knife.
Valency
Metals have 1 to 3 electrons in the outermost shell of their atoms.
Conduction
Metals are good conductors because they have free electrons. Silver is the best conductor of heat and electricity. Lead is the poorest conductor of heat. Bismuth, mercury and iron are also poor conductors
Density
Metals have high density and are very heavy. Iridium and osmium have the highest densities where as lithium has the lowest density.
Melting and Boiling Point
Metals have high melting and boiling point - Tungsten has the highest melting point where as Hg has low boiling point. Na and K have low melting points.
Chemical Properties of Metals
Metals are Electropositive Elements
Metals loose electrons and form positively charged ions, therefore metals are called electropositive elements. Sodium metal forms sodium ions Na+, Mg forms positively charged Megnesium ions Mg2+ and aluminium forms aluminium ions Al3+.
Reaction of Metals with Oxygen
Metals are very reactive. They form compounds with other elements easily. Sodium (Na) and potassium (K) are some of the most reactive metals. Metallic oxides make hydroxides (bases) (OH-) and not acids when in solution. The oxides of metals are basic in nature, with the exception of Cr2O3 being acidic and Al, Zn, Pb oxides being amphoteric.
Potassium, sodium, lithium, calcium and magnesium react with oxygen and burn in air.Metals from aluminium to copper react slowly when heated in air, to form the metal oxides. Aluminium is the fastest and copper is the slowest of the six.
Sodium metal reacts with the oxygen of the air at room temp to form sodium oxide. Hence sodium is stored under kerosene to prevent its reaction with oxygen, moisture, and carbon di oxide.
- 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 oxidised to give rust.
- On heating in air it burns with a brilliant flame forming triferric tetroxide
- Copper is the least reactive metal and hence copper metal does not burn in air even on heating. However, on prolonged strong heating it reacts with oxygen and forms copper(II) oxide outside and copper(I) oxide 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 react with steam (but not H2O(I)), to form the metal oxide and hydrogen gas.
- Red hot iron reacts with steam to form Iron (II,III) oxide.
Note:-
Note that the reaction between iron and steam is reversible . Tin ,lead,copper,silver,gold and platinum do not react with water or steam.
Reaction of Metals with Dilute Acids
- Potassium, sodium, lithium and calcium react violently with dilute H2SO4(aq) and dilute HCl(aq). The reaction is similar to the reaction with water, forming the metal salt (either sulphate or chloride) and hydrogen gas.
- 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 and Sulphuric acids because these acids are strong oxidizing agents.
