Metals and Non-metals

IMPORTANT NOTES 

1. Element is a substance which cannot be further subdivided into simpler substances by any physical or chemical means.

2. Metals are the elements (except hydrogen) which form positively charged ions by losing electrons from their valence shell and form oxides which are basic in nature. 

3. Non-metals are the elements which form negatively charged ions by accepting electrons in their valence shell and form acidic or neutral oxides. 

4. All metals have one to three electrons in their valence shell. 

5. All non-metals have four to seven electrons in their valence shell. 

6. Physical Properties of Metals Metals generally : 

(i) are solids, 

(ii) are hard, 

(iii) have lustre, 

(iv) have high densities, 

(v) have high melting and boiling points, 

(vi) are malleable, 

(vii) are ductile, 

(viii) have high tensile strength, 

(ix) are good conductors of heat and electricity, 

(x) are monoatomic, 

(xi) and can form alloys. 

7. Physical Properties of Non-metals Non-metals generally : 

(i) are brittle solids or gases, 

(ii) are soft, 

(iii) have low densities, 

(iv) have no lustre, 

(v) have low melting and boiling points, 

(vi) are not malleable, 

(vii) are not ductile, 

(viii) have no tensile strength, 

(ix) are bad conductors of heat and electricity, 

(x) are polyatomic, 

(xi) do not form alloys. 

8. Chemical Properties of Metals : 

(i) Metals generally react with oxygen to form their oxides which are basic in nature. 

(ii) Metal oxides of aluminium, zinc, lead and tin react with alkalises as well as acids. Such oxides are called amphoteric oxides. 

(iii) Active metals like potassium, sodium, calcium, magnesium, aluminium, zinc and iron react with water or steam to form their hydroxides/oxides and hydrogen gas. 

(iv) Active metals react with dilute mineral acids to form their respective salts and hydrogen gas. 

(v) Active metals displace less active metals from their aqueous salt solutions. The reaction which takes place is called chemical displacement reaction. 

(vi) A table of metals arranged in the order of their decreasing chemical reactivity, is called metal reactivity series. 

9. Chemical Properties of Non-metals : 

(i) Non-metals generally react with oxygen to form their oxides, which are either neutral or acidic in nature. 

(ii) Neutral oxides of non-metals are CO, NO, H2O and N2O. 

(iii) Non-metals do not displace hydrogen from water or dilute mineral acids. 

(iv) Non-metals react with one another to form covalent compounds. 

(v) Non-metals react with metals to form ionic compounds. 

10. An atom or an ion having duplet or octet configuration like noble gases is said to be in the minimum state of energy and hence is chemically inactive. 

11. The atoms of an element can attain stable electronic configuration of the nearest noble gas : 

(i) by donating (losing) one or more electrons from their valence shell to another atom, 

(ii) by accepting (gaining) one or more electrons in their valence shell from another atom, 

(iii) by sharing electrons from their valence shell with another atom/atoms. 

12. The atom which accepts or donates electron/ electrons from its valence shell so as to acquire a configuration of the nearest noble gas gets electrically charged and becomes an ion.

13. The metals generally donate electrons from their valence shell and hence form positively charged ions. These positively charged ions are called cations, because, they discharge at the cathode to form neutral atoms. 

14. The non-metals generally accept electrons in their valence shell and hence form negatively charged ions. The negatively charged ions are called anions, because, they discharge at the anode to form neutral atoms. 

15. Characteristics of Cations : 

(i) Only metals form cations, because, they have 1 to 3 electrons in their valence shell which they can easily donate to acquire a stable configuration of the nearest noble gas. 

(ii) There is no change in atomic number of an element as it forms a cation, because, the number of protons do not change. 

(iii) The atomic radii of a cation is smaller than neutral atom, because of the disappearance of the valence shell. 

16. Characteristics of Anions : 

(i) Only non-metals form anions, because, they have 4 to 7 electrons in their valence shell. Thus, they accept electrons in their valence shell to acquire a stable configuration of the nearest noble gas. 

(ii) There is no change in the atomic number of an anion as the number of protons in it are the same as in the neutral atom.

(iii) The atomic radii of an anion slightly increases, because the effective pull of the nucleus slightly decreases due to addition of extra electron/electrons in the valence shell. 

17. Electropositive elements : The elements which have a tendency to donate electrons from their valence shell and become positively charged ions (cations) are called electropositive elements. All metals and hydrogen are electropositive elements. E – e– E+ from Metal valence shell Cation 

18. Electronegative elements : The elements which have a tendency to accept electrons in their valence shell and become negatively charged ions (anions) are called electronegative elements. All non-metals are electronegative elements. E+ e– E– into Non-metal valence shell Anion.

19. Electrovalent bond or Ionic bond : A chemical bond formed between two different atoms, by the transfer of one or more electrons from the valence shell of an electropositive or metallic element to the valence shell of a nonmetallic element, is called an electrovalent bond or an ionic bond. 

20. Electrovalency : The number of electrons which an atom of an element donates or accepts in its valence shell, so as to have a stable configuration like that of the nearest noble gas is called electrovalency. 

21. Electropositive valency : The number of electrons which an atom of an element (metal or hydrogen) donates from its valence shell, so as to have a stable configuration like that of a noble gas, is called electropositive valency. 

22. Electronegative valency : The number of electrons which an atom of an element (nonmetal) accepts in its valence shell, so as to have a stable configuration like that of a noble gas is called electronegative valency. 

23. Electrovalent compound or Ionic compound: The chemical compound formed as a result of transfer of electrons from the valence shell of an atom (metal or hydrogen) of an element to the valence shell of an atom of another element (non-metal) is called electrovalent compound or ionic compound. 

24. Properties of Electrovalent (ionic) Compounds : 

(i) They are generally hard and crystalline solids. 

(ii) They are generally non-volatile and hence have high melting and boiling points. 

(iii) They are good conductors of electricity in the fused state. 

(iv) They are generally soluble in water and their aqueous solutions are good conductors of electricity. 

(v) The chemical reaction between the aqueous solutions of ionic compounds is very fast.

25. Metallurgy encompasses various processes in the extraction of a metal from its ore and then refining the metal including study of its properties and uses. 

26. Gangue or Matrix are the unwanted impurities, such as sand, stones, mud, limestone, mica, etc. associated with the naturally occurring ore. 

27. Dressing of ore involves processes, (such as hand picking, grinding and crushing and pulverizing) which give an ore such a physical form, so that gangue can be easily removed from the ore. 

28. Concentration of ore involves processes, which help in the removal of gangue from the dressed ore, thereby increasing the concentration of the metal in the ore. 

29. Electromagnetic separation is the concentration process followed for the dressed ore, if 

(i) the ore is magnetic in nature. 

(ii) ore contains magnetic impurities (such as Fe2O3). 

30. Gravity process or Hydraulic washing method of concentration is followed for such dressed ores which have metallic ores of high density as compared to the density of gangue. It is not followed in case of sulphide ores. 

31. Froth floatation process for the concentration is followed for sulphide ores only. In this process, the sulphide ore is immersed in a mixture of pine oil and water and then strongly agitated with compressed air. The sulphide ore rises up along with the froth produced by the oil, but the gangue sinks to the bottom. 

32. Chemical method for the concentration of ore is followed for such ores (ore of aluminium), in which density of the ore and the gangue is almost same. 

33. Calcination is the process of heating the concentrated ore in the absence of air, such that it decomposes to form its metallic oxide. Following are the objectives achieved during calcination: 

(i) removes moisture from the ore 

(ii) makes the ore porous 

(iii) expels the volatile impurities 

(iv) decomposes carbonate ores to oxide ores. 

34. Roasting is the process of heating the concentrated ore (only sulphide ores) in the presence of excess of air, such that it changes to the oxide ore. Following are the objectives achieved during roasting : 

(i) removes moisture from the ore 

(ii) makes the ore porous 

(iii) expels the volatile impurities 

(iv) oxidises sulphide ores to oxide ores. 

35. Smelting or reduction of ore is the process of conversion of the metal oxide ore into metal, by reducing it with a suitable reducing agent. The reducing agents commonly used are coke, carbon monoxide and hydrogen. For reducing ores of highly active metals, electrolytic reduction is employed. 

36. Refining of metals is done by a number of methods. However, the best method is electrolytic method. In this method the pure metal is made the cathode, and the impure metal is made the anode. The cathode and the anode are immersed in the aqueous solution of metal. On the passage of electric current, the pure metal from the anode is transferred to the cathode. 

37. Thermite mixture consists of three parts of ferric oxide and one part of powdered aluminium. It is commonly employed in spot welding, such as broken railway lines. 

38. Alloy is a homogeneous mixture of two or more metals, obtained by melting them together. 

39. (a) Major alloys of aluminium are 

(i) Duralumin or Dural [A1 = 95%; Cu = 4%; Mn = 0.5%; Mg = 5%] 

(ii) Magnalium [Al = 95%; Mg = 5%] 

(b) Major alloys of iron are 

(i) Stainless steel [Fe = 73% – 80%; C = 1.0%; Cr = 18%; Ni = 1%] 

(ii) Manganese steel [Fe = 83% – 84%; Mn = 15%; C = 1% – 1.5%]

(iii) Tungsten steel [Fe = 79% – 85%; W = 10% – 20%; C = 1%] 

(iv) Alnico [Fe = 60%; Al = 12%; Ni = 20%, Co = 5%] 

(c) Major alloys of copper are : 

(i) Aluminium bronze [Cu = 90%; Al = 10%] 

(ii) Brass [Cu = 60% – 80%; Zn = 20% – 40%] 

(iii) Bronze [Cu = 80%; Zn = 10%; Sn = 10%] 

(iv) Gun metal [Cu = 88%; Sn 10%; Zn = 1% – 2%] 

(v) German silver [Cu = 30% – 60%; Zn = 25% – 35%; Ni = 15% – 35%]. 

40. Gold is alloyed with metals like copper, silver, cadmium, so as to make it hard and workable at low temperature. 

41. Purity of gold is measured in carats. 100% pure gold is 24 carat, while 1 carat = 4.1666 g per 100 g of alloy. 

42. Corrosion of metals is the formation of layers of undesirable compounds on the surface of metals due to the action of moist air containing impurities. 

43. Corrosion of metal take place only, if the surface of metal comes in direct contact with moist air for prolonged time. 

44. Rusting : The slow conversion of iron into hydrated ferric oxide in the presence of moist air is called rusting. 

45. Rust is a flaky, non-sticky brown powder formed on the surface of iron, when the iron is exposed to moist air. 

46. Factors which promote rusting : In addition to moist air : 

(i) the presence of salts such as sodium chloride, 

(ii) presence of more active metals than iron and the presence of pollutants such as NO2; SO2; CO2 in air, promote rusting. 

47. Rusting can be prevented by coating the metal surface with 

(i) red lead 

(ii) paints 

(iii) enamel 

(iv) oil or grease 

(v) plastic coating 

(vi) galvanising 

(vii) tinning 

(viii) electroplating with nickel or chromium 

(ix) converting iron into stainless steel.