Class 10 Science Metals and Non Metals Exam Notes

Class 10 Science Metals and Non Metals Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Introduction

There are 115 elements known till today. These elements can be classified into various groups on the basis of their properties. Metals are usually hard, malleable and ductile. They are sonorous and have metallic lustre. They are good conductors of heat and electricity.

Non-metallic are usually soft. They do not possess lustre. They are not malleable and ductile rather they are brittle. They are not good conductors of heat and electricity.

We shall study about metals and non-metals in detail.

Important Terms And  Concepts

1.Metals : Those elements which can lose electrons easily and from positive ions. They are mostly solids, possess high density. They have high melting and boiling points. They have metallic lustre and they are sonorous, i.e., produce metallic sound. They are good conductors of heat and electricity. They are usually malleable and ductile, e.g., gold , silver, copper, tin, lead, iron, mercury, cobalt, nickel, aluminium, sodium, potassium are metals.

2.Hardness : Most of the metals are hard. If you try to cut them with knife, it will not be possible in most of the metals. Some of metals like sodium, potassium are soft metals and can be cut with knife.

3.Malleability : The ability of a metals due to which it can be beaten into sheets is called malleability. Iron, copper, zinc, aluminium, magnesium are available in the form of sheets. Aluminium, steel, copper, brass, bronze are used in making utensils.

Brass and bronze are also used for making statues. Bronze is used for making medals. Aluminium and silver metals are converted in foils. Aluminium foils are used for packaing whereas silver foils are used in decorating sweets.

4.Ductility : It is the ability of metals due to which it can be drawn into wires. Copper, aluminium, iron can be drawn into wires. Silver, gold and platinum are highly ductile metals. 1 gram of gold can be drawn into 2 km long wire.

5.Effect of Tapping (Sonorous) : When metals are struck with hard substance, they produce sound, i.e., they are sonorous. Brass and bronze are highly sonorous. They are used in making bells and gongs.

6.Electrical Conductance : It is the property due to which electric current can pass through the metal. It is due to presence of free electrons or mobile electrons, e.g., copper, silver, gold, aluminium are good conductors of electricity. Silver is best conductor of electricity followed by copper, gold, aluminium and tungsten. Mercury and lead have low electrical conductivity due to high resistance.

7.Thermal Conductivity : It is the property due to which metals can conduct heat e.g., copper, silver, aluminium, gold and iron are good conductors of heat.

8. Metallic Lustre : Most of metals have shiny surface e., they show metallic lustre e.g., Au, Ag, Pt are lustrous.

9. Exceptions if classification of metals and non-metals is done on the basis of physical properties :

(i) All metals are hard except sodium, potassium, lithium, They can be cut even with knife. Osmium (Os) is hardest metal. Lithium is lightest metal.

(ii) All metals are solids except mercury. Cesium, francium, germanium and gallium are low melting solids. Gallium becomes liquid if kept on palm. But gallium has very high boiling point which makes it useful for high temperature thermometers.

(iii) Iodine is a non-metals but has metallic lustre. Diamond (an allotrope of carbon) is highly lustrous.

(iv) Non-metals have low melting and boiling points but diamond, graphite, boron and silicon have high melting and boiling points.

(v) Metals have high melting and boiling points. Tungsten has highest melting point whereas sodium, potassium have low melting and boiling points.

(vi) Non-metals are bad conductors of heat and electricity, but graphite is a non-metals which is good conductor of heat and electricity.

(vii) Metals generally have high density e.g., Cu, Cr, Ag, Au, Pt, Os, Ir, Ti, W, etc. Sodium, potassium, and lithium have density less than 1 g cm–3. Diamond is non-metals but still has high density.

(viii) Generally, metals have 1 to 3 valence electrons. Hydrogen has one valence electron but still it is non- metal. Helium has 2 valence electrons but still it is non-metals.

(ix) Metals usually have a bright metallic lustre and are silvery white in appearance, but gold is yellow in colour, copper is reddish brown.

(x) Non-metals generally do not from alloys but carbon is alloyed with iron to form steel.

Thus metals and non-metals cannot be classified on the basis of physical properties only. Chemical properties are more suitable to classify them.

10. Anodising : The process of forming oxide layer on the surface of metal is called anodising, g., Aluminium forms an oxide layer on its surface when exposed to air. It is non-penetrating layer which protects it from corrosion. The layer can be made more thick with the help of anodising. It is a process in which cleaned aluminum metals is taken as anode. Dilute H2SO4 acts as electrolyte. When electric current is passed, O2 gas is liberated which reacts with aluminium to form a layer of aluminium oxide.
The oxide layer can be made coloured like red, blue, etc., so as to make it more attractive for making decorative articles.
Metal burns in presence of oxygen to from metal oxide. Let us perform and experiment.

11. Solubility of Oxides in water : Some metal oxides are soluble in Soluble base are called alkalies e.g.,

12. Alkalies : Those base, which are soluble in water are called For example, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide Ca(OH)₂ etc. They turn phenolphthanlein pink and turn red litmus blue.

13. Basic Oxides : Those oxide, which react with acids or acidic or acidic oxides to form salt and water are called basic Metals react with oxygen to form metallic oxides which are generally basic in nature e.g., Na2O (sodium oxide.) CaO (calcium oxide), K2O (potassium oxide), MgO (magnesium oxide) are basic oxides.

MgO + HCl → MgCl₂ + H₂O

14.Acidic oxides : Those oxides, which react with bases or basic oxides to form salt and water, are called acidic oxides. Non-metals react with oxygen to form non-metallic oxides which are generally acidic in nature, e.g., CO₂ (carbon dioxide), SO2 (sulphur dioxide), SO3 (sulphur trioxide), P₂O₅ (phosphorus pentoxide), SiO₂ (silicon dioxide) are acidic oxides.

CO₂ + 2NaOH ® Na₂CO₃ + H₂O

15. Amphotoric oxide : These oxides are both acidic as well as basic in nature. They react both with acids as well as bases to form salt and water. Some metals form amphoteric oxides. ZnO (zinc oxide) and Al2O3 (aluminium oxide) are amphoteric oxides.

16.Neutral Oxides : These oxides are neither acidic nor basic in nature. They neither react with acids nor with bases. Some non-metals form neutral oxides. Carbon monoxide (CO), nitrogen oxide (NO), Nitrous oxide (N₂O) are examples of neutral oxides.

17.Electrovalent Compounds : The compounds in which metal loses electrons and non-metal gains electrons are called electrovalent compounds, e.g., NaCl (sodium chloride), KCl (potassium chloride), etc.

18. Hydrides : When metals react with hydrogen, the compounds formed are called hydrides. e.g., sodium hydride (NaH), calcium hydride (CaH2). In these compounds, metals lose electrons whereas hydrogen gains electron.

19. Reaction of metal oxides with Acids : Metal oxides react with acid to form salt and water because most of the metal oxides are basic or amphoteric in nature. Amphoteric oxides react with both acids as well as bases.

20. Reactivity of Metals : All the metals do not react with the same rate. Some react very fast, some react moderately whereas others react very slowly e.g., sodium, potassium react with oxygen at room
temperature vigorously to form oxide. They can catch fire in presence of moist air. These metals are kept in kerosene oil or benzene so as to protect them from formation of oxide and hydroxide in open air.
At room temperature, metals like Al, Zn, Cu, Mg, Sn, Pb form oxide layer on their surface and become dull. This oxide layer makes aluminium passive and does not allow it to react further with H2O, O2 and even conc. HNO₃. Copper is less reactive and forms black coloured oxide and gives green coloured flame with blue tip in burner. Magnesium burns with dazzling light forming MgO. Silver, gold and platinum do not react with oxygen. Mercury forms red coloured oxide, HgO.

Reactivity Series of Metals :
The series of metals in decreasing order of reactivity is called reactivity or activity series of metals. The metals at the top are most reactive whereas metals at the bottom are less reactive. The following is activity series of metals. The metals above hydrogen are more reactive than hydrogen. They can displace hydrogen from dilute acids and water. Metals below hydrogen are less reactive than hydrogen and cannot displace hydrogen from dilute acids and water.

21. Reaction of Metals with Water : Some metals like Na, K, Ca react with cold water vigorously to form hydroxide and liberate hydrogen gas. Some metals like Mg, Zn, Al react with hot water to form oxides and hydroxides and hydrogen gas. Some metals like Fe reacts with steam to form Fe3O4 and H2(g). Some metals like Cu, Ag, Au, Hg, Pb and Pt do not react with water at all because they are less reactive than hydrogen. Let us perform the following experiment.

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