In many teaching exams including CTET 2020, UPTET 2020 STET 2020 etc. Science may be an interesting subject having and 30 questions of Science content and 30 questions of Science Pedagogy in CTET and other State TET Exams. Science comprising of various branches of studies like chemistry, physical science, and life science.
Metals & Non-Metals
- At present there are 115 known elements.
- There are similarities as well as differences in the properties of these elements.
- On the basis of their properties, elements can be divided into metals and non-metals.
- Physical Properties of Metals
- Physical State:
All metals are solids at room temperature.
Exceptions: Mercury and gallium are liquids at room temperature.
All metals in their pure state have a shine and can be polished to give a highly reflective surface.
Metals have the ability to withstand high tensile strength and can be made into thin sheets. This property of metals is called malleability.
Metals can also be drawn into thin wires. The ability of metals to be drawn into wires is called ductility. Example: Gold and silver are the most ductile metals.
- Conduction of Heat:
Metals are good conductors of heat and have high melting points.
Example: Silver and copper are very good conductors of electricity.
Exceptions: Lead and mercury are poor conductors of heat.
- Conduction of Electricity:
Metals are good conductors of electricity.
All electric wires are made of copper.
- Hardness :
Metals are generally hard, and their hardness varies from metal to metal. Alkali metals such as sodium and potassium are soft metals and can be easily cut with a knife.
- Melting & Boiling Points:
Metals usually have high melting and boiling points.
Tungsten has the highest melting point whereas sodium and potassium have low melting points.
Metals which produce a sound on striking a hard surface are said to be sonorous.
- Physical Properties of Non-Metals
- Non-metals are either in the solid or gaseous state.
Exception: Bromine is an exception which exists in the liquid state.
- Non-metals do not have lustre.
Exception: Iodine crystals are lustrous.
- They do not possess the property of hardness.
Exception: Carbon in the form of diamond is the hardest substance, which has a high melting and boiling point.
- Non-metals are poor conductors of heat and electricity.
Exception: Graphite, an allotrope of carbon conducts electricity.
- Chemical Properties of Metals
- Reaction of Metals with Oxygen
Almost all metals react with oxygen to form metal oxides.
- Sodium and potassium are the most reactive and react with oxygen present in the air at room temperature to form the oxides.
4Na + O2 → 2Na2O
4K + O2 → 2K2O
- Magnesium does not react with oxygen at room temperature, but on heating, it burns in the air with intense light and heat to form magnesium oxide.
2Mg + O2 → 2MgO
- Reaction of Metals with Water
Metals react with water to produce metal oxides with the release of hydrogen gas. But all metals do not react with water.
- Metals such as sodium and potassium react vigorously with cold water to lead to evolution of hydrogen, which immediately catches fire producing a large quantity of heat. 2K + 2H2O → 2KOH + H2 + Heat
2Na + 2H2O → 2NaOH + H2 + Heat
- Metals such as aluminium, zinc and iron do not react with cold or hot water, but they react with steam to form metal oxides and hydrogen. 2
Al + 3H2O → Al2O3 + 3H2
3Fe+ 4H2O → Fe3O4+ 4H2
- Reactions of Metals with Acids
Metals react with acids to form salt and hydrogen gas.
- Metals react with dilute hydrochloric acid to give metal chloride and hydrogen gas.
Mg + 2HCl → MgCl2 + H2
Zn + 2HCl → ZnCl2 + H2
- Metals react with sulphuric acid to form metal sulphate and hydrogen gas.
Fe + H2SO4 → FeSO4 + H2
Zn + H2SO4 → ZnSO4 + H2
- Metals react with nitric acid, but hydrogen gas is not evolved since nitric acid is a strong oxidizing agent. So, it oxidizes the hydrogen to water and itself gets reduced to a nitrogen oxide. But magnesium and manganese react with dilute nitric acid to evolve hydrogen gas.
Mg + 2HNO3 → Mg (NO3)2 + H2
Mn + 6HNO3 → Mn (NO3)2 + H2
- Reactivity Series
The arrangement of metals in the order of decreasing reactivity is called the reactivity series of metals.
- Reactions of Metals with Solutions of Other Metal Salts
A more reactive metal displaces a less reactive metal from its salt solution. For example:
When an iron nail is placed in a copper sulphate solution, the blue color of CuSO4 fades away slowly and a reddish brown copper metal is formed.
CuSO4 (aq) + Fe(s) → FeSO4 (aq) + Cu(s)
- Reaction of Metals with Chlorine
Metals react with chlorine to form metal chlorides.
- Sodium readily reacts with chlorine to form ionic chloride called sodium chloride.
2Na(s) + Cl2 (g) → 2NaCl(s)
- Calcium reacts vigorously with chlorine to form calcium chloride. Ca(s) + Cl2(g) → 2CaCl2(s)