- Alloys are homogeneous mixtures of metals (or metals with non-metals) with different properties than pure metals—often harder, less conductive, and with lower melting points.
- 24-carat gold is soft, so 22-carat gold (an alloy with copper or silver) is used in jewellery to improve strength.
- Solder, an alloy with a low melting point, is used to join electrical wires.
- Corrosion prevention methods include painting, galvanising, anodising, electroplating, and alloying.
- Galvanising, tinning, anodisation, and electroplating all involve protective coatings to prevent corrosion, while alloying enhances durability and resistance.
Definitions [5]
Definition: Electropositive Elements
Metals are reactive. They lose electrons easily and become positively charged ions. That is why metals are called electropositive elements.
Definition: Ionic Compounds
The compounds formed in this manner by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.
Definition: Minerals
The elements or compounds, which occur naturally in the earth’s crust, are known as minerals.
OR
Minerals are the naturally occuring compounds of metals which are generally mixed with other substances such as soil, mud, sand, silica (Si02) limestone, rocks, etc. These earthly impurities are called gangue or matrix.
Definition: Ores
At some places, minerals contain a very high percentage of a particular metal, and the metal can be profitably extracted from it. These minerals are called ores.
OR
Ores are those minerals from which metals are extracted commercially at a comparatively lower cost and with minimum effort.
Definition: Corrosion
Corrosion is the gradual damage of metals caused by their reaction with components of the atmosphere, such as oxygen and moisture.
Key Points
Key Points: Physical Properties of Metals
- Metals are mostly solids at room temperature; mercury and gallium are exceptions and exist in liquid form.
- Metals have a shining surface called metallic lustre, which may decrease due to oxidation or reaction with gases.
- Malleability allows metals to be beaten into thin sheets (gold and silver are highly malleable), and ductility allows them to be drawn into wires (gold is the most ductile).
- Metals are good conductors of heat and electricity, with silver and copper being excellent conductors.
- Most metals are hard with high melting and boiling points, but alkali metals (sodium, potassium) are soft and low‑melting, and metals are sonorous, producing sound when struck.
Key Points: Physical Properties of Non-metal
- Most metals are solids at room temperature, but mercury is a liquid, and gallium and caesium melt in the palm of the hand due to their very low melting points.
- Alkali metals (lithium, sodium, potassium) are soft, low-density metals with low melting points, unlike most metals.
- Iodine, though a non-metal, shows a metallic lustre, which is unusual for a non-metal.
- Carbon exists in allotropes: diamond is the hardest natural substance, and graphite is a good conductor of electricity.
- Nonmetals are usually non-lustrous, soft, poor conductors, and exist in solid or gas states, with bromine being the only liquid non-metal.
Key Points: Electronic Configurations
- Metals react by losing electrons to form positively charged ions (cations), while non-metals gain electrons to form negatively charged ions (anions), in order to attain a stable electronic configuration (octet or duplet).
- Ionic compounds consist of aggregates of oppositely charged ions held together by strong electrostatic forces of attraction, and do not exist as molecules.
Key Points: Chemical Properties of Metal
- Most metals form basic oxides with oxygen; aluminium and zinc oxides are amphoteric.
- Reactivity with oxygen varies; sodium and potassium react quickly and are kept in kerosene.
- Metals may react with water to form hydroxides and release hydrogen gas, depending on temperature.
- Metals react with dilute acids to give salt and hydrogen gas; copper and nitric acid are exceptions.
- More reactive metals can displace less reactive ones; this forms the basis of the reactivity series.
Key Points: Properties of Ionic Compounds
- Physical nature: Ionic compounds are solids, generally hard and brittle, due to the strong force of attraction between positive and negative ions.
- Melting and boiling points: Ionic compounds have high melting and boiling points because a large amount of energy is required to break the strong inter-ionic attraction.
- Solubility: Ionic (electrovalent) compounds are generally soluble in water but insoluble in solvents like kerosene and petrol.
- Conduction of electricity: Ionic compounds do not conduct electricity in the solid state but conduct in the molten state or in solution, as the ions are free to move and carry an electric current.
Key Points: Occurrence of Metals
- Metals occur in either the free or combined state, depending on their reactivity.
- Metals are grouped as low, medium, or highly reactive, and each group has a different extraction method.
- Ores have impurities called gangue, which are removed before extraction.
- Low-reactive metals are extracted by heating alone; medium-reactive metals require roasting or calcination, followed by reduction.
- Highly reactive metals (such as Na, Mg, and Al) are extracted by electrolysis.
- Metals are purified by electrolytic refining, where pure metal deposits at the cathode and impurities form anode mud.
Key points: Prevention of Corrosion
Important Questions [21]
- Arrange the following metals in the increasing order of their reactivities: Copper, Zinc, Aluminium, and Iron
- Why is sodium kept immersed in kerosene oil?
- ‘E’ is an element which reacts with oxygen to form an oxide E2O. An aqueous solution of E2O turns red litmus blue, so
- An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be:
- A student added few pieces of aluminium metal to two test tubes A and B containing aqueous solutions of iron sulphate and copper sulphate. In the second part of her experiment,
- Why is acidified water considered to be a good conductor of electricity?
- Write the Name and Formula of a Molecule Made up of Three Atoms of Oxygen.
- Write the Chemical Equation for the Following Reaction: Manganese Dioxide is Heated with Aluminum Powder.
- Write a Chemical Equation to Illustrate the Use of Aluminium for Joining Cracked Railway Lines.
- Explain the Following: Reactivity of Aluminium Decrease If It is Dipped in Nitric Acid.
- Write the Chemical Equation for the Following Reaction: Cinnabar is Heated in the Presence of Air.
- Where Does the Metal Aluminium, Used in the Process, Occurs in the Reactivity Series of Metals?
- Write the Chemical Equation for the Following Reaction: Calcium Metal Reacts with Water.
- Write a chemical equation showing the ionic products formed on dissolving potassium hydroxide in water.
- Metal oxides generally react with acids, but few oxides of metal also react with bases. Such metallic oxides are: MgO ZnO Al2O3 Cao
- Select the appropriate state symbols of the products given as X and Y in the following chemical equation by choosing the correct option from table given below: ZnA(s)+HA2SOA4(l)⟶ZnSOA4(X)+HA2(Y)
- No Chemical Reaction Takes Place When Granules of a Solid, A, Are Mixed with the Powder of Another Solid, B
- Bronze is an alloy of ______.
- Answer the following question. What are alloys?
- Answer the following question. List two properties of alloys.
- What is "Rusting"? Describe with a Labelled Diagram an Activity to Investigate the Conditions Under Which Iron Rusts.
