Metals occur in nature in free as well as combined form. The Earth’s crust is the major source of metals.Some metals are found in the earth’s crust in the free state, such as gold, silver, mercury etc.and some are found in the form of their compounds owing to their higher reactivity.
Metals are also found in seawater in the form of many soluble salts.such as sodium chloride, magnesium chloride, etc on the basis of reactivity, metals are grouped into three categories, namely, Metals of low reactivity, Metals of medium reactivity and Metals of high reactivity.The method of extraction of a metal from its ore depends on the metal’s position in the reactivity series: Metals found in a combined state in the earth’s crust are known as minerals. The minerals that have a relatively high concentration of metal and can be extracted in an easy and cost-effective process, are called ores.
Minerals:
Minerals may be defined as any naturally occurring inorganic solids that have a definite chemical composition and possesses a crystalline structure.
Ores:
Ores are naturally occurring in rocks that contain metal or metal compounds in sufficient amounts to make it profitable for extracting them. Example, Sulphide ore, Oxide ore, Carbonate ore.
- Metals at the bottom of activity series like gold, platinum, silver, copper generally occur in the free state. But copper and silver also occur in sulphide and oxide ores.
- Metals of medium reactivity (Zn, Fe, Pb etc.) occur mainly as oxides, sulphides or carbonates.
- Metals of high reactivity (K, Na, Ca, Mg and Al) are very reactive and thus found in the combined state.
Gangue:
Impurities like sand, rock and other impurities surrounding the mineral of interest in an ore. It is the commercially worthless mineral matter associated with economically valuable metallic minerals in a deposit
Metallurgy:
The process of extraction of metals from their respective metallic compounds is termed as metallurgy.
The step-wise process of obtaining metal from its ore:
- Enrichment of ore
- Obtaining metal from enriched ore.
- Refining of impure metal to obtain the pure metal.
Extracting metals low in the activity series:
Done by heating the ores in the air at high temperature.
Mercury from cinnabar:
2HgS + 3O2 +Heat → 2HgO + 2SO2
2HgO +Heat → 2Hg + O2
Extracting metals middle in the activity series:
Metals are easier to obtain from oxide ores, thus, sulphide and carbonate ores are converted into oxides.
- Metal ore heated strongly in excess of air (Roasting):
2ZnS + 3O2 +Heat → 2ZnO + 2SO2
- Metal ore heated strongly in limited or no supply of air (Calcination):
ZnCO3 +Heat → ZnO + CO2
Reduction of metal oxide:
- USING COKE: Coke as a reducing agent.
ZnO + C +Heat → Zn + CO
- USING DISPLACEMENT REACTION: highly reactive metal like Na, Ca and Al are used to displace metals of lower reactivity from their compounds.
MnO2 + 4Al +Heat → 3Mn + 2Al2 O3 + heat
Fe2 O3 + 2Al +Heat → 2Fe + Al2O3 + heat
In the above reaction molten iron is formed and is used to join railway tracks. This is called thermite reaction.
Extracting metals top in the activity series:
These metals have more affinity for oxygen than carbon and are obtained by electrolytic reduction.
Sodium is obtained by electrolysis of its molten chloride NaCl → Na+ + Cl
- As electricity is passed through the solution metal gets deposited at cathode and non-metal at the anode.
- At cathode : Na + + e – → Na
- At anode : 2Cl – → Cl2 + 2e –
Refining of metals:
- Impurities present in the obtained metal can be removed by electrolytic refining.
- Copper is obtained using this method.
Following are present inside the electrolytic tank:
- Anode – a slab of impure copper.
- Cathode – a slab of pure copper.
- Solution – aqueous solution of copper sulphate with some dilute sulphuric acid.
- From anode, copper ions are released in the solution and an equivalent amount of copper from solution is deposited at the cathode.
- Impurities containing silver and gold gets deposited at the bottom of the anode as anode mud.
Elements are divided mainly into two groups on the basis of physical and chemical properties – Metal and Non-metals
Metals that are chemically active get corroded in the presence of air and moisture in the atmosphere. Metals with a higher reactivity (such as magnesium, aluminum, iron, zinc, and tin) are much more prone to corrosion.
Corrosion is a natural process, which converts a refined metal to a more chemically stable form, such as its oxide, hydroxide, or sulphide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. Corrosion degrades the useful properties of materials and structures including strength, appearance, and permeability to liquids and gases.
Corrosion is the deterioration of a metal as a result of chemical reactions between it and the surrounding environment.
Metals are attacked by substances in surroundings like moisture and acids:
- Silver – it reacts with sulphur in the air to form silver sulphide and turns black.
- Copper – reacts with moist carbon dioxide in the air and gets a green coat of copper carbonate.
- Iron-acquires a coating of a brown flaky substance called rust. Both air and moisture are necessary for rusting of iron.
Prevention of corrosion:
- The application of a paint coating is a cost-effective way of preventing corrosion. Paint coatings act as a barrier to prevent the transfer of electrochemical charge from the corrosive solution to the metal underneath.
- Applying a powder coating: In this process, a dry powder is applied to the clean metal surface. The metal is then heated which fuses the powder into a smooth unbroken film. A number of different powder compositions can be used, including acrylic, polyester, epoxy, nylon, and urethane.
- Corrosion is mainly caused by a chemical reaction between the metal and gases in the surrounding environment. By taking measures to control the environment, these unwanted reactions can be minimized.
Reducing exposure to rain or seawater, controlling the amounts of sulfur, chlorine, or oxygen in the surrounding environment are some of the measures to be taken.
- Galvanizing: coating the metal with an additional metal type that is more likely to oxidize
The most common example is the coating of iron alloy steel with zinc, a process known as galvanizing. This protection is used for steel pipelines carrying water or fuel, water heater tanks, ship hulls, and offshore oil platforms.
Coating the iron alloy steel with a less active metal, such as tin. Tin will not corrode, so the steel will be protected as long as the tin coating is in place.
- A light coat of a protective material, such as metal oxide, creates a protective layer over the metal which acts as a barrier against corrosion. This is used in petroleum refining, chemical production, and water treatment works.
- Rusting of iron is prevented by painting, oiling, greasing, galvanizing, chrome plating, anodizing and making alloys.
Alloys:
An alloy is a mixture of two elements, one of which is a metal.
Alloys often have properties that are different to the metals they contain.
Generally, alloys are stronger and harder than their main metals, less malleable (harder to work) and less ductile (harder to pull into wires). This makes them more useful than the pure metals.
- Adding a small amount of carbon makes iron hard and strong.
- Stainless steel is obtained by mixing iron with nickel and chromium. It is hard and does not rust It is used to produce utensils,kitchen ware bathroom fixtures, buildings, power tools, weaponry, and even jewelry.
- Mercury is added to other metals to make an amalgam.
- Brass: It is an alloy of copper and zinc. It is used to make musical instruments, coins, handicrafts, and household fixtures such as doorknobs and faucets.etc
- Bronze: It is an alloy of copper and tin. It can be made into furniture, armour and weapons. It is used in construction and ship building.
In brass and bronze, melting point and electrical conductivity are lower than that of pure metal.
- Solder: It is an alloy of lead and tin. Has a low melting point and is used for welding electrical wires.
A metal is an element that is characterised by its hardness, opacity and a shiny surface. When elements of one metal combine with other elements, they become compounds. Metals are generally good conductors of heat and electricity. A non-metal is an element or compound that lacks the attributes of a metal.
In the periodic table, about 91 of the 118 elements are metals and the rest are non-metals and metalloids. Some elements appear in both metallic and non-metallic forms.
In this lesson, you are going to learn about the physical properties of metals and non-metals.
Physical properties of Metals and Non-metals
Physical Properties of Metals
The following are the physical properties of metals:
• Solid at room temperature except for mercury
• Ductile (can be drawn into wires)
• Malleable (can be beaten into thin sheets)
• Sonorous (can produce sound)
• Lustrous (contain a natural shine)
• Have a high melting point except for cesium and gallium that have a very low melting point
• Generally good conductors of heat and electricity. While silver and copper are the best conductors of heat, lead and mercury are comparatively very poor conductors of heats
• Have high density except for sodium and potassium. They can be cut with a knife as they have low density
• Metals form basic oxides like Magnesium oxide (MgO)
Physical Properties of Non-Metals
The following are the physical properties on non-metals:
• Found in the form of solids or gasses. Only bromine is found in the form of a liquid
• Generally bad conductors of heat and electricity except for graphite, which is a natural form of carbon, is a good conductor
• Non-sonorous
• Non-lustrous, only iodine has luster
• Non-metals form acidic oxides (as in acid rain)
Metals have a tendency to lose electrons and form cations. They react with oxygen, present in the air to form metal oxides.
For example, potassium burns in seconds while iron will rust over a long period of time, in fact it may take a number of years to oxidise. The common oxides of metals are basic in nature while those of non-meals are acidic.
Non-metals have relatively high ionisation energy and a higher electronegativity. They exist as anions or oxyanions in aqueous solutions, and form ionic or interstitial compounds when mixed with metals.
Chemical Properties of Metals
Reaction with air:
- Some metals oxidise and some don't when exposed to air but some metals actually burn or combust when they come in contact with air
- Metal + Oxygen → Metal Oxide
- Example:
- Metals like Magnesium (Mg), Aluminium (Al), Zinc (Zn) and Lead (Pb) react slowly with air and form a protective layer
- Magnesium can also burn in air with a white dazzling light to form its oxide
- Iron (Fe) and copper (Cu) combine with oxygen to form an oxide over a period of time, and this process is called rusting
- Metals like Sodium (Na) and Potassium (K) are kept immersed in kerosene oil as they react vigorously with air and catch fire
Reaction with dilute acids:
- Metals react with dilute hydrochloric acid and dilute sulphuric acid to form a salt and hydrogen gas
- Metal + Dilute acid → Salt + Hydrogen gas
- Example: Fe + 2HCl → FeCl2 + H2
Reaction with water:
- Most reactive metals like Sodium reacts with cold water to produce hydrogen and sodium hydrxide
- Example: Na + H2O → NaOH + H2
- In the case of Calcium (Ca) and Magnesium (Mg), the metal starts floating due to bubbles of hydrogen gas sticking to its surface
- Example: Al + H2O → Al2O3 + H2
Reaction of metals with other metal salts:
- All metals are not equally reactive. Reactive metals can displace less reactive metals from their compounds in solution. This forms the basis of reactivity series of metals
- Metal A + Salt solution of A → Salt solution of metal A + Metal B
Reaction of metals and non-metals:
- Reactivity of elements is described as a tendency to attain a completely filled valence shell
- Atoms of metals can lose electrons from valence shells to form cations (+ve ions)
- Atoms of non-metals gain electrons in valence shell to form anions (–ve ions)
- Oppositely charged ions attract each other and are held by strong electrostatic forces of attraction forming ionic compounds
Properties of Ionic Compounds
Ionic compounds:
- Are solid and mostly brittle
- Have high melting and boiling points. More energy is required to break then strong inter-ionic attraction
- Generally soluble in water and insoluble in kerosene, petrol
- Conduct electricity in solution and in a molten state. In both cases, free ions are formed and conduct electricity
Chemical Properties of Non-Metals
Reaction with oxygen:
- Non-metals react with oxygen to form non-metallic oxides
- These oxides are acidic oxides because they react with water to form acids
- Example: Sulphur burns in air to form sulphur dioxide and sulphur dioxide reacts with water to form sulphurous acid
Reaction with water: Non-metals do not react with water
Reaction with acids:
- Most non-metals do not react with acids.
- Some non-metals like sulphur react with concentrated nitric acid to form sulphur dioxide, nitrogen dioxide and water
How do Metals and Non - Metals React
Ionic compounds are produced when metals react with non-metals but when a non-metal reacts with another non-metal, usually a molecular compound is formed. At room temperature, ionic compounds are hard and brittle solids, while molecular compounds are usually in the form of gases, liquids or low melting solids.
In this lesson, you will learn about the reactivity of metals and non-metals.
Ionic Bonds
Ions are charged particles that form, when atoms (or clusters of atoms) lose or gain electrons; metal atoms lose electrons to form positively charged ions.
Ionic bond is a type of chemical bond that involves electrostatic attraction between oppositely charged ions, and is the primary interaction occurring in ionic compounds.
Ionic Compounds
Ionic compounds are formed when metals and non-metals react. They are hard, brittle solids at room temperature and unable to conduct electricity. When in molten or liquid state, that is when they are dissolved in water or a solvent, they conduct electricity.
Properties of Ionic Compounds
- Non-metal atoms gain electrons to form negatively charged ions
- Physical Nature: Though hard due to electrostatic forces of attraction, ionic compounds are brittle and break under pressure
- Solubility: Soluble in water, insoluble in organic solvents like benzene and toluene
- Melting and boiling points: High due to strong inter-ionic attraction
- Conduction of electricity:
- When in a molten or dissolved state, ions are able to move to opposite electrodes and hence electricity is conducted
- Unable to conduct electricity in a solid state