Metals and Non-Metals
Chapter: Metals and Non-Metals
Any element that has tendency to lose electron and become more stable is called a metal, because of this property of loosing electrons, metals are said to be electropositive in nature. All the metals except mercury are solids at room temperature.
Why Study Metals?
It is important to study metals because most of the things we use in our daily life are made of metals. Nails which are used in furniture making, hammer, and body of the car, gold jewellery, fencing wire, and electrical appliances like refrigerator are some of the examples of metal made materials.
History of Metals
Gold was the first metal to be discovered in 6000 BC and that is because gold is non reactive and exists in free form. After the discovery of gold other metals have been discovered which are as follows:
copper, silver, lead, tin, iron, mercury, platinum, antimony, bismuth, zinc, arsenic, cobalt, nickel, manganese, tungsten, uranium, titanium, beryllium, chromium, potassium, sodium, boron, barium, calcium, magnesium, strontium, silicon, aluminium.
Physical Properties of Metals:
1 . Metallic Lusture:
Most of the metals in general in their pure state show a shining surface. This property of metals is called metallic lusture.
Example: gold, silver, copper.
If you would like to observe metallic lusture take small pieces of Iron, copper, aluminum from your lab and clean the surface by rubbing with a sand paper.
2 . Hardness:
Metals are generally hard in nature and the hardness varies from metal to metal. Not all the metals are hard , example: sodium is not hard whereas gold, silver and iron are hard.
3 . Malleability:
The property of any metal being beaten to thin sheets is called malleability. Most of the metals are malleable in nature, example: gold, silver and iron are the most malleable metals.
Activity: You can check malleability of metals by yourself, just take piece of iron, zinc or copper from your lab and place it on a hard block of iron and strike it four to five times with a hammer.You can observe that the thickness of the metal decreases as it becomes into a sheet.
4 . Ductility:
The ability of metals to be drawn into thin wires is called ductility, example: gold is the most ductile metal. A wire of 2km can be drawn from 1gm gold.
5 . Good Conductors of Heat:
Most of the metals are good conductors of heat, example: aluminium and copper are used as cooking utensils as they can with stand heat.
6 . High Melting Point:
The melting point (or, rarely, liquefaction point) of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exists in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard pressure. Metals have high melting and boiling points, examples: tungsten has high melting point and silver has low melting point.
7 . Good Conductore of Electricity:
Metals are good conductors of electricty. Examples; The electrical wiring is made of copper.
8 . Sonorous:
Metals make noise, so metals are said be sonorous, examples: bells in the temple, they make noise. Bells in temple are usually made out of bronze.
9 . High Density:
Metals have high density and are very very heavy.iridium and osmium have high densities while lithium has low density, example: weights which are used in grocery shops are heavy and they are nothing but metals.
Chemical Properties of Metals
Metals are very reactive. Metals tend to lose 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
Almost all the metals when burnt combine with oxygen to form metal oxides.
1 - Mg does not react with oxygen at room temperature. On heating, Mg burns in air with intense light and heat to form MgO.
Some metals form metal oxides without burning as they are highly reactive.
2 - 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.
Reaction of metals with acids
Metals are bases in nature, so they combine with acids to produce metal salt( acid+ base= salt).
- 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.
Reaction of metals with water:
Sodium reacts vigorously with cold water forming sodium hydroxide and hydrogen.
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 colorless when dilute. During the displacement, the blue solution loses its color and the iron metal is seen to turn into pink-brown as the displaced copper becomes deposited on it.
Extraction of Metals:
Mining is the process of extracting metals from the earth. We get ores which are rich sources of the vital elements of metals. Some prospecting techniques are used to locate an ore, then exploration and examination of deposits are done. Surface mines and sub surface mines are the two types of mineral sources. Surface mines are mined by excavation using heavy equipment.
The metals must be extracted once the ore is mined and this extraction is done by chemical or electrolytic reduction. Process of Pyrometallurgy uses high temperatures to convert ore into raw metals and the process of hydrometallurgy uses aqueous chemistry for the same purpose. The methods of extraction used depend on the metal and their constituents.
If the metal ore is an ionic compound of a metal and non-metal, then the ore should be smelted to extract the pure metal. Smelting is process of heating with a reducing agent. Iron is one such metal which is smelted and it uses carbon as a reducing agent. Metals like sodium and aluminium are extracted using electrolysis. Sulphide ores are roasted in air to convert them into oxides as they can’t be reduced directly to the metal.
Applications of Metals:
➤ Some metals and metallic alloys have high structural strength and this property makes them useful for carrying large loads or resisting impact damage.
➤ Metal alloys can be processed to have high resistance to shear, torque and deformation.
➤ The strength and resistance of metals has led to their numerous uses in high building and bridge constructions, and also in many vehicles, appliances, tools, pipes, non-illuminated signs, and rail road tracks.
➤ Iron and aluminium are the two commonly used metals which are available in plentiful in the earth’s crust.
➤ Metals are good conductors of electricity so they are extensively used in manufacturing electrical appliances and also for delivering an electric current over a distance with little loss of energy. Home electrical systems are wired with copper wire because of its good conducting properties..
➤ Some metals are highly reflective and this nature is vital in the construction of mirrors and some astronomical instruments. This property can also make metallic jewellery aesthetically appealing.
➤ Some metals which are radioactive such as uranium and plutonium are used in nuclear nuclear power plants to produce energy through nuclear fission. Mercury which is a liquid at room temperature, is used in switches to complete a circuit when it flows over the switch contacts
Non-metal is a chemical element that lacks metallic properties. Examples of non metals are carbon. Sulphur, iodine, oxygen and hydrogen. 17 elements are generally classified as non-metals. The non metals are either solids(carbon, phosphorus) or gases(fluorine, neon) except Bromine which is a liquid.
Physical Properties of Non-Metals
- Highly volatile
- Low elasticity
- Good insulators of heat and electricity
- Have high ionisation energy(energy needed to remove one electron from a gaseous atom or ion) and electro-negativity values
The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds. They are also called as electrovalent compounds.
Properties of Ionic Compounds
- Ionic compounds are brittle in nature.
- They have high melting points and high boiling points
- They are soluble in water and insoluble in solvents
- They conduct electricity in molten state
Iron after some time gets rust. It happens because of corrosion. Corrosion is defined as the gradual destruction of materials (usually metals) by chemical reaction with their environment
Prevention of Corrosion
Rust is formed on iron after some duration of time. It can be prevented by processes like oiling; greasing, painting, galvanizing, anodizing etc. galvanization is defined as a process of applying zinc on the surface of steel or iron to protect them from rusting. Alloying is a process used to improve the metal properties. Lets us take an example. Iron is mixed with chromium and nickel to obtain stainless steel. Steel is hard and doesn’t undergo rusting. Such compounds formed by mixing two or more metals are called an alloy. An alloy is defined as homogenous mixture of two or more metals or a metal and non metal. For an alloy, the electrical conductivity and melting point is less than a pure metal. Brass which is a good conductor of electricity is an alloy of copper and zinc. But copper is a very good conductor of electricity and is used for making electrical circuits.