Chemical Properties of Metals (Class 10)

Chemical prorties of Metals.
Chapter 3 (Class 10)

1. CHEMICAL Dr. Pranabjyoti Das Arunodoi Junior College 06-May-21 1 Pranabjyoti Das

2. Metals can be well described only on the basis of their chemical properties. 1) Reaction of metals with oxygen Almost all metals react with oxygen to form metal oxide , but the reactivity differs for different metals. Metals react with oxygen to form metal oxides. Metals donate electrons to oxygen for the formation of metal oxides. Metal + Oxygen  Metal oxide 4K + O 2  → 2 K 2 O 06-May-21 2 Pranabjyoti Das

3. Chemical properties of Metals Sodium is the most reactive metals . Sodium reacts with oxygen in air at room temperature to form sodium oxide. Hence, sodium is stored under kerosene oil to prevent its reaction with oxygen, moisture and carbon dioxide 4Na + O 2 → 2Na 2 O Potassium is also a reactive metal. Like sodium, potassium also reacts instantly with oxygen to produce potassium oxide 4K + O 2  → 2 K 2 O 06-May-21 3 Pranabjyoti Das

4. Most M etal oxides are insoluble in water . B ut some of the metal oxides dissolve in water to form alkalis, and they are basic in nature Example: S odium oxide Na 2 O and potassium oxide K 2 O dissolve in water to produce alkalis Na 2 O+ H 2 → 2NaOH K 2 + H 2 → 2KOH 06-May-21 4 Pranabjyoti Das

5. Magnesium does not react with oxygen at room temperature . B ut on heating , M agnesium , burns in air with intense light and heat to form magnesium oxide ( MgO ) 2Mg + O 2 → 2MgO Zinc burns in air on heating to form zinc oxide 2Zn + O 2 → 2ZnO Iron filings burn in the flame of the burner 3Fe + 20 2 heat → Fe 3 4 06-May-21 5 Pranabjyoti Das

6. Copper is least reactive. It does not burn, but on heating , the hot metal is coated with a black coloured layer of copper oxide 2Cu + O 2 → 2CuO Aluminium develops a thin layer of oxide when exposed to air 4Al + 30 2 → 2Al 2 O 3 06-May-21 6 Pranabjyoti Das

7. Amphoteric oxides Metal oxides are usually basic in nature but some metal oxides such as aluminium oxide ( Al 2 O 3 ) and zinc oxide ( ZnO ) react both with acids as well as bases to produce salt and water . Such metal oxides are called as Amphoteric Oxides. Al 2 O 3 + 6HCl → 2AlCl 3 + 3H 2 O Al 2 O 3 + 2NaOH → 2NaAlO 2 + H 2 06-May-21 7 Pranabjyoti Das

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9. Metals like potassium and sodium react vigorously with cold water to liberate hydrogen gas which immediately catches fire producing a lot of heat . ( Exothermic reaction) 2K + 2H 2 O → 2KOH + H 2 + Heat 2Na+ 2H 2 O → 2NaOH + H 2 + H eat 2. Reaction of Metals with Water 06-May-21 9 Pranabjyoti Das

10. Reaction of Na with water 06-May-21 10 Pranabjyoti Das

11. Calcium reacts with water less vigorously . The heat evolved is not sufficient for hydrogen to catch fire . Ca + 2H 2 O → Ca(OH) 2 + H 2 Magnesium reacts with hot water to form magnesium hydroxide Mg(OH) 2 and hydrogen hydrogen gas . Mg + H 2 O → Mg (OH) 2 + H 2 06-May-21 11 Pranabjyoti Das

12. Metals like aluminium, iron and zinc do not react either with cold or hot water but they react with steam to form their respective metal oxide and hydrogen gas. 2Al + 3H 2 O → Al 2 O 3 + 3H 2 3Fe + 4H 2 O → Fe 3 O 4 + 4H 2 Metals like G old , S ilver , Platinum and C opper do not react with water at all . So they are called as noble metals 06-May-21 12 Pranabjyoti Das

13. 3) Reaction of metals with acids Metals react with acids to give salt and hydrogen gas . Let us see the following reactions…. Mg + 2HCl → MgCl 2 + H 2 ↑ 2Al + 6 HCl → 2AlCl 3 + 3H 2 ↑ Zn + 2HCl → ZnCl 2 + H 2 ↑ Fe +2HCl → FeCl 2 + H 2 ↑ The reactivity decreases in the order, Mg > Al > Zn > Fe Copper doesn’t react with acids as Copper is less active than Hydrogen. 06-May-21 13 Pranabjyoti Das

14. Nitric acid HNO 3 And Metals…. Hydrogen gas is not evolved when a metal reacts with nitric acid, as it is a strong oxidizing agent . It oxidizes the hydrogen to water and itself gets reduced to any of the nitrogen oxides ( N 2 , nitrous oxide ; NO , nitric oxide ; NO 2 nitrogen dioxide etc) But magnesium and M anganese react with dilute HNO 3 to evolve hydrogen gas Mg + 2HNO 3 → Mg(NO 3 ) 2 + H 2 ( magnesium + nitric acid → magnesium nitrate + hydrogen ) 06-May-21 14 Pranabjyoti Das

15. Element Reaction with Air Reaction with Water Reaction with Acid Potassium Sodium Burns vigorously to form oxides With cold water forms hydrogen gas and alkaline hydroxide solution. React with decreasing vigour down the series till Ca Violent reaction to give hydrogen gas and salt solution Calcium Magnesium Aluminium Zinc and Iron Burn with decreasing vigour down the series Mg reacts with hot water to fomi magnesium hydroxide and hydrogen gas. For Al, Zn and Fe, no reaction with cold and hot water. With steam forms metal oxide and hydrogen gas React to form hydrogen gas and salt solution with decreasing vigour down the series Reactions of metals with air , water and acids 06-May-21 15 Pranabjyoti Das

16. 4. Reactions of metals with solutions of metal salts Let us put an iron nail in a solution of copper sulphate . The iron nail gets coated with a reddish brown colour copper and the blue colour of copper sulphate solution fades out. In this reaction more reactive iron has displaced copper which is less reactive from the copper sulphate solution 06-May-21 16 Pranabjyoti Das

17. This reaction is known as displacement reaction. The brown coating on the iron nail shows that copper is deposited on the iron nail by displacing iron The greenish colour of the solution in the test tube shows that Fe 2+ ions are present in the solution. This shows that iron is more reactive than copper, as Fe 2+ ions have displaced Cu 2+ ions from copper sulphate solution Fe + CuSO 4 → Cu + FeSO 4 Metal A + Salt solution B → Salt solution A + Metal B 06-May-21 17 Pranabjyoti Das

18. 5. Reaction of M etals with N on-metals Let us look at the electronic configuration of some metals and non-metals. It will help us to understand the reactivity of different elements and formation of different compounds We have learnt that noble gases have a completely filled valance shell, hence are chemically inactive 06-May-21 18 Pranabjyoti Das

19. Electronic configuration of some metals and non-metals Type of element Element Atomic number Electronic configuration K L M N Metals Sodium (Na) l l 2 8 1 Magnesium (Mg) 12 2 8 2 Aluminium (Al) 13 2 8 3 Potassium (K) 19 2 8 8 1 Calcium (Ca) 20 2 8 8 2 Non-metals Nitrogen (N) 7 2 5 Oxygen (O) 8 2 6 Fluorine (F) 9 2 7 Phosphorus (P) 15 2 8 5 Sulphur (S) 16 2 8 6 Chlorine (Cl) l7 2 8 7 06-May-21 19 Pranabjyoti Das

20. Sodiu m is a silver coloured metal that reacts so violently with water that flames are produced due to formation of hydrogen gas . On the otherhand , Chlorine is a greenish coloured gas which is so poisonous that it was used as a weapon in World War l When chemically bonded together, these two dangerous substances form a compound sodium chloride so safe that we eat it every day (common table salt) 06-May-21 20 Pranabjyoti Das

21. Sodium (2 . 8 . 1 ) atom has one electron in its outermost shell. If it loses one electron from its "M" shell then its "L" shell becomes the outermost shell to acquire a stable octet. The nucleus of this atom still has 11 protons but the number of electrons has become 10, so there is a net positive charge giving us S odium cation (Na + ) On the other hand chlorine (2, 8, 7) has 7 electrons in its outermost shell and requires one more electron to complete its octet 06-May-21 21 Pranabjyoti Das

22. Formation of Sodium Chloride ( NaCl ) 2.8.1 2.8.7 06-May-21 22 Pranabjyoti Das

23. Ionic or E lectrovalent C ompound Sodium and chloride ions being oppositely charged attract each other and by strong electrostatic forces of attraction to exist as sodium chloride ( NaCl ), resulting in the formation of an electrovalent or ionic bond compound. Such a bond formed by the give and take of electrons is called as ionic or electrovalent bond. Compounds formed in this manner by the transfer of electrons from a metal Na to a non-metal Cl are known as ionic compounds or electrovalent compounds 06-May-21 23 Pranabjyoti Das

24. Properties of ionic compounds Ionic compounds are solids and hard due to strong force of attraction between positive and negative ions They are generally brittle and break into pieces when pressure is applied Ionic compounds have high melting and boiling points, as a considerable amount of energy is required to break the strong inter molecular attraction They are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc. 06-May-21 24 Pranabjyoti Das

25. Ionic compounds in the solid state do not conduct electricity because the movement of ions in the solid state is not possible due to their rigid structure, but they conduct electricity in the molten state. The conduction of electricity through a solution involves the movements of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution 06-May-21 25 Pranabjyoti Das

26. Thank You Dr. Pranabjyoti Das Arunodoi Junior College Tangla 06-May-21 26 Pranabjyoti Das