The electrons present in the outermost shell of an atom are called Valence electrons. From the Bohr-Bury scheme, we find the outermost shell of an atom can accommodate a maximum of 8 electrons. Also, the atoms of the elements show little chemical activity if its outermost shell is completely filled. Also can be said that the elements combining capacity or its valency is zero. In the inert elements, the helium atoms have two electrons in their outermost shell and all other elements have atoms with 8 electrons in the outermost shell.
The combining capacity of atoms of other elements to react or form molecules with atoms of the same or different elements were the attempts to attain a fully filled outmost shell.
An outermost shell that has 8 electrons is said to be octet.
The atoms would attempt or react to achieve an octet in the outermost shell and this process will be done by gaining, losing, or sharing the electrons.
The losing, gaining, or sharing of electrons gives the direct combining capacity of the elements.
Example Sodium/lithium/hydrogen atoms contain one electron each in its outermost shell so as to lose one electron. These elements are said to have a valency of One (1).
Example Sodium/lithium/hydrogen atoms contain one electron each in its outermost shell so as to lose one electron. These elements are said to have a valency of One (1).
Similarly, the valency of Magnesium is 2, as it has 2 electrons in the outermost shell and aluminum is 3 as it has 3 electrons in the outermost shell.
Valency of Metals
Metals have positive valency as they have +1,+2,+3 electrons in their outermost or valance shell.
The metal having valency ‘1’ is potassium its chemical symbol is K . Potassium is an alkali metal and belongs to Group 1 of the periodic table.
Combining capacity Meaning
It is the ability to make bonds with other elements. The number of valence electrons of an atoms given the combining capacity.
Metal having valency 1
Alkali metals has one valency electrons. These belongs to first group of periodic table. Ex: Hydrogen.
Valence or Valency of an element is the measure of combining capacity with other atoms when it forms chemical compounds of the molecule. Below is the list of Valencies of all 118 elements with symbols.
Valencies of Elements 1 to 4
Elements 1 to 4 are Hydrogen, Helium, Lithium, and Beryllium.
. Hydrogen(H) : 1,0,-1
2. Helium (He): 0
3. Lithium (Li): 1,-1
4. Beryllium (Be): 2
Valencies and Symbols of elements 1 to 4 include Hydrogen, Helium, Lithium, and Beryllium
Hydrogen Valency
Hydrogen its symbol is ‘H‘ has only one valence electron and can form only one bond with an atom that has an incomplete outer shell.
Helium Valency
Helium, its symbol is ‘He‘. Helium only has two electrons in its S-orbit. One Orbit can have only two electrons. As a result, its duplet is fulfilled. As a result, it has no tendency to lose or gain electrons. Due to this, its valency is zero.
Lithium Valency
Lithium, its symbol is ‘Li‘. Lithium Valency is 1. This is because the atomic number of lithium is 3 and electronic configuration = 2,1. Li (Z=3). To attain stability, Lithium needs to lose one electron. Lithium li number of valence electrons is 1.
Beryllium Valency
Beryllium, its symbol is ‘Be‘. Beryllium Valency is 2. Beryllium’s atomic number is 4. Its electronic configuration is 1s² 2s². It has two electrons in its Valence shell and when the valence shell electrons are more than 4. Then the valency = 8-n..
As its valence shell has 2 electrons present for sharing. Two electrons can be easily donated. As a result valency of Beryllium is two.
Valencies of Elements 5 to 9
5. Boron (B): 3,2,1
6. Carbon (C): 4,3,2,1,-1,-2,-4
7. Nitrogen (N): 5,4,3,2,1,0,-1,-2,-3
8. Oxygen (O): 2,1,0,-1,-2
9. Fluorine (F): 0,-1
Valencies and Symbols of element 5 to 9 that includes Boron, Carbon, Nitrogen, Oxygen, and Fluorine
Nitrogen has either 3 or 5 Valence electrons. This is because it can bond in the outer orbitals 2p and 2s.
Valencies of Elements 10 to 14
Valency of Neon
Neon valency is 0, this is because it has completely filled the outermost shell as it is a noble gas. As it is an inert gas and its electronic configuration is 1s2,2s2,2p6. All its orbital is full. Due to this Neon is the least reactive and there is no true compound of Neon has been synthesized.
Neon valency is zero because Neon is a noble, inert, and non-reactive gas.
10. Neon (Ne): 0
11. Sodium (Na): 1, -1
12. Magnesium (Mg): 2
13. Aluminium (Al): 3, 1
14. Silicon (Si): 4,3,2,1,-1,-2,-4
Valencies and Symbols of element 10 to 14 that includes Neon, Sodium, Magnesium, Aluminum, and Silicon
Valencies of Elements 15 to 19
16. Sulfur (S) : 6,5,4,3,2,1,0,-1,-2
17. Chlorine (Cl): 6,5,4,3,2,1,0,-1,-2
18. Argon(Ar): 0
19: Potassium (K): 1, -1
Valencies and Symbols of elements 15 to 19 that include Phosphorus, Sulfur, Chlorine, Argon, and Potassium
Valency of Argon
The atomic number of argon is 10. Its electronic configuration is (2,8). The atom is stable as the outermost shell is complete, and the outermost electron is 8. Also, argon belongs to the group of noble gases and its valance shells are completely filled as they have no tendency to lose or gain electrons. As a result, the valency of Argon is 0.
Valency of Potassium
The electronic configuration of Potassium is 2,8,8,1. Also, its valence shell has 1 electron. As a result, the valency of Potassium is 1.
Valencies of Elements 20 to 24
20. Calcium (Ca): 2
21. Scandium (Sc): 3,2,1
22. Titanium (Ti): 4,3,2,0,-1,-2
23. Vanadium (V): 5,4,3,2,1,0,-1,-2
24. Chromium (Cr): 6,5,4,3,2,1,0,-1,-2,-3,-4
Valencies and Symbols of Elements 20 to 24 that include Calcium, Scandium, Titanium, Vanadium and Chromium
Valencies of Elements 25 to 29
25. Manganese (Mn): 7,6,5,4,3,2,1,0,-1,-2,-3
26. Iron (Fe): 6,5,4,3,2,1,0,-1,-2
27. Cobalt (Co): 5,4,3,2,1,0,-1
28. Nickel (Ni): 6,4,3,2,1,0,-1
29. Copper(Cu): 4,3,2,1,0
Valencies and Symbols of Elements 25 to 29 that include Manganese, Iron, Cobalt, Nickel and Copper
Valencies of Elements 30 to 34
30. Zinc (Zn) : 2,1,0
31. Gallium (Ga): 3,2,1
32. Germanium(Ge): 4,3,2,1
33. Arsenic (As): 5,3,2,-3
34. Selenium (Se): 6,4,2,1,-2
Valencies and Symbols of Elements 30 to 34 include Zinc, Gallium, Germanium, Arsenic and Selenium
Valency of Zn (Zinc)
The atomic number of Zinc is 30. The Valence shell contains 2 electrons. The electronic configuration of Zinc is 1s22s22p63s23p63d104s2 . As Zinc has 30 electrons, which is 28 in the first three wheels and 2 in the fourth.
In order to achieve octet, it has to gain six or other otherwise lose two electrons. There, it loses two electrons in the outermost shell and forms a 2+. As a result, Zinc has a Valency of two(2).
Valencies of Elements 35 to 39
35. Bromine (Br): 7,5,4,3,1,0,-1
36. Krypton (Kr): 2,0
37.Rubidium (Rb): 1,-1
38. Strontium (Sr): 2
39. Yttrium (Y): 3,2
Valencies of Elements 40 to 44
40. Zirconium(Zr): 4,3,2,1,0,-2
41. Niobium (Nb): 5,4,3,2,1,0,-1,-3
42. Molybdenum (Mo): 6,5,4,3,2,1,0,-1,-2
43. Technetium (Tc): 7,6,5,4,3,2,1,0,-1,-3
44. Ruthenium (Ru): 8,7,6,5,4,3,2,1,0,-2
Valencies and Symbols of Elements 40 to 44 include Zirconium, Niobium, Molybdenum, Technetium and Ruthenium
Valency of Ruthenium (Ru)
Ruthenium has 8 valence electrons. The total number of electrons in RU is 44. Its atomic number is 44.
Its atomic weight is 101.07. Its melting point is 2,250° C (4,082° F). Its boiling point is 3,900° C (7,052° F). Its specific gravity is 12.30 (20° C).
Ruthenium valence is 1,2,3,4,5,6,7,8. Also it’s electron configuration is 2-8-18-15-1 or (Kr)4d75s1.
Valencies of Elements 45 to 49
45. Rhodium (Rh): 6,5,4,3,2,1,0,-1
46. Palladium (Pd): 4,2,0
47. Silver (Ag): 3,2,1,0
48. Cadmium (Cd): 2,1
49. Indium (In): 3,2,1
Valencies and Symbols of Elements 45 to 49 include Rhodium, Palladium, Silver, Cadmium and Indium
Valencies of Elements 50 to 54
50. Tin (Sn): 4,2,-4
51. Antimony (Sb): 5,3,-3
52. Tellurium (Te): 6,5,4,2,1,-2
53. Iodine (I): 7,5,3,1,0,-1
54. Xenon (Xe): 8,6,4,3,2,0
Valencies and Symbols of Elements 50 to 54 include Tin, Antimony, Tellurium, Iodine and Xenon
Valencies of Elements 55 to 59
55. Cesium (Cs): 1,-1
56. Barium (Ba): 2
57. Lanthanum (La): 3,2
58. Cerium (Ce): 4,3,2
59. Praseodymium (Pr): 4,3,2
Valencies and Symbols of elements 55 to 59 that include Cesium, Barium, Lanthanum, Cerium and Praseodymium
Valencies of Elements 60 to 64
60. Neodymium (Nd): 4,3,2
61. Promethium (Pm): 3
62. Samarium (Sm): 3,2
63. Europium (Eu): 3,2
64. Gadolinium (Gd): 3,2,1
Valencies and Symbols of elements 60 to 64 that include Neodymium, Promethium, Samarium, Europium and Gadolinium
Valencies of Elements 65 to 69
65. Terbium (Tb): 4,3,1
66. Dysprosium (Dy): 4,3,2
67. Holmium (Ho): 3,2
68. Erbium (Er): 3
67. Thulium (Tm): 3,2
Valencies and Symbols of elements 65 to 69 that include Terbium, Dysprosium, Holmium, Erbium and Thulium
Valencies of Elements 70 to 74
70. Ytterbium (Yb) : 3,2
71. Lutetium (Lu): 3
72. Hafnium (Hf): 4,3,2,1
73. Tantalum(Ta): 5,4,3,2,1,-1,-3
74. Tungsten (W): 6,5,4,3,2,1,0,-1,-2,-4
Valencies and Symbols of elements 70 to 74 that include Ytterbium, Lutetium, Hafnium, Tantalum, and Tungsten
Valencies of Elements 75 to79
75. Rhenium (Re): 7,6,5,4,3,2,1,0,-1,-3
76. Osmium (Os): 8,7,6,5,4,3,2,1,0,-2
77. Iridium (Ir): 6,5,4,3,2,1,0,-1
78. Platinum (Pt): 6,5,4,2,0
79. Gold (Au): 7,5,3,2,1,0,-1
Valencies and Symbols of elements 75 to 79 that include Rhenium, Osmium, Iridium, Platinum and Gold
Valencies of Elements 80 to 84
80. Mercury (Hg): 2,1
81. Thallium (Tl): 3,1
82. Lead (Pb): 4,2
83. Bismuth (Bi): 5,3,1,-3
84. Polonium (Po): 6,4,2,-2
Valencies and Symbols of Elements 80 to 84 that include Mercury, Thallium, Lead, Bismuth and Polonium
Lead Valency
The valency of lead is 2,4. Its atomic number is 82 and its electronic configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p2. Due to inert pair effect, Pb displays +2 valency.
Valencies of Elements 85 to 89
85. Astatine (At): 7,5,3,1,-1
86. Radon (Rn): 2, 0
87. Francium (Fr): 1
88. Radium (Ra): 2
89. Actinium (Ac): 3
Valencies and Symbols of elements 85 to 89 that include Astatine, Radon, Francium, Radium, and Actinium
Valencies of Elements 90 to 94
90. Thorium (Th): 4,3,2
91. Protactinium (Pa): 5,4,3
92. Uranium (U): 6,5,4,3,2
93. Neptunium (Np): 7,6,5,4,3,2
94. Plutonium (Pu): 7,6,5,4,3,2
Valencies and Symbols of elements 90 to 94 that include Thorium, Protactinium, Uranium, Neptunium, and Plutonium
Valencies of Elements 95 to 99
95. Americium (Am): 7,6,5,4,3,2
96. Curium (Cm): 6,5,4,3,2
97. Berkelium (Bk): 4,3,2
98. Californium (Cf) : 5,4,3,2
99. Einsteinium (Es) : 4,3,2
Valencies and Symbols of elements 95 to 99 that includes Americium, Curium, Berkelium, Californium, and Einsteinium
Valencies of Elements 100 to 104
100. Fermium (Fm): 4,3,2
101. Mendelevium (Md): 3,2,1
102. Nobelium (No): 3,2
103. Lawrencium (Lr): 3, 2
104. Rutherfordium (Rf): 4, 3
Valencies and Symbols of elements 100 to 104 that include Fermium, Mendelevium, Nobelium, Lawrencium and Rutherfordium
Valencies of Elements 105 to 109
105. Dubnium (Db): 5,4
106. Seaborgium (Sg): 6, 5, 4
107. Bohrium (Bh): 7,6,5,4,3
108. Hassium (Hs): 8,7,4,3,2
109. Meitnerium (Mt): 6,5,4,3,2,1
Valencies and Symbols of Elements 105 to 109 include Dubnium, Seaborgium, Bohrium, Hassium and Meitnerium
Valencies of elements 110 to 114
110. Darmstadtium (Ds) : 6,5,4,3,2,1
111. Roentgenium (Rg): 3,-1
112. Copernicium (Cn): 2,1
113. Nihonium (Nh): 1
114. Flerovium (Fl): 2
Valencies and Symbols of elements 110 to 114 that include Darmstadtium, Roentgenium, Copernicium, Nihonium and Flerovium
Valences of Elements 115 to 118
115. Moscovium: 3,1
116. Livermorium (Lv): 4,2
117. Tennessine (Ts): Unknown
118. Oganesson (Og): 8,6,4,2
Valencies and Symbols of elements 115 to 118 that include Moscovium, Livermorium, Tennessine, Oganesson
| compound | element | Valency |
| NaCl | Na or Cl | 1 |
| MgO | Mg | 2 |
| AlCl3 | Al | 3 |
| HCl | H or Cl | 1 |
| CH4 | C | 4 |
Variable Valency
Certain elements show more than one valency which is called variable valency. Most of the d- block elements (transition metals) shows variable valency.
The compound in which the metal has higher valency is called ‘-ic’ compound while the compound in which metal has lower valency is called an ‘-ous’ compound. Eg.
| Metal | Valency | Molecular formula | Name of compound | IUPAC name |
| Fe | 2 | FeO | Ferrous oxide | Iron(I) oxide |
| 3 | Fe2O3 | Ferric oxide | Iron(II) oxide | |
| Cu | 1 | Cu2O | Cuprous oxide | Copper(I) oxide |
| 2 | CuO | Cupric oxide | Copper(II) oxide | |
| Hg | 1 | HgCl or Hg2Cl2 | Mercurous chloride | Mercury(I) chloride |
| 2 | HgCl2 | Mercuric chloride | Mercury(II) chloride | |
| Ag | 1 | AgCl | Argentous chloride | Silver(I) chloride |
| 3 | AgCl3 | Argentic chloride | Silver(III) chloride | |
| Au | 1 | AuCl | Aurous chloride | Gold(I) chloride |
| 3 | AuCl3 | Auric chloride | Gold(III) chloride | |
| Sn | 2 | SnCl2 | Stannous chloride | Tin(II) chloride |
| 4 | SnCl4 | Stannic chloride | Tin(IV) chloride | |
| Pb | 2 | PbCl2 | Plumbous chloride | Lead(II) chloride |
| 4 | PbCl4 | Plumbic chloride | Lead(IV) chloride |
Certain elements can have more than two valencies. For example, valency of S in H2S, SO2 and SO3 is 2, 4 and 6 respectively.
Radicals (Ions)
Most of the inorganic compounds are made up of two oppositely charged units called radicals or ions. Eg.
Radicals (ions) are atoms or group of atoms which carry positive or negative charge and behave as a single unit during a chemical reaction.
Depending upon the nature of charge, radicals are of two types:-
The radicals containing positive charge and derived from base are called basic radicals. Eg.
hydrogen(H+), calcium( Ca++), aluminium(Al+++), ammonium(NH4+), etc.
2. Acidic radical or electronegative radical or anion :
The radicals containing negative charge and derived from acid are called acidic radicals. Eg.
Chloride (Cl–), oxide(O– –), sulphate(SO4– –), etc.
Some important electropositive radicals :
- Sodium = Na+
- Calcium = Ca++
- Zinc = Zn++
- Ammonium = NH4+
- Aluminium = Al+++
- Silicon = Si4+
- Cuprous = Cu+
- Cupric = Cu++
- Mercurous = Hg+
- Mercuric = Hg++
- Aurous = Au+
- Auric = Au3+
- Ferrous = Fe++
- Ferric = Fe3+
Some important electronegative radicals :
- Chloride = Cl –
- Oxide = O – –
- Hydroxide = OH –
- Sulphide = S – –
- Sulphate = SO4 – –
- Sulphite = SO3 – –
- Thiosulphate = S2O3 – –
- Bisulphate = HSO4–
- Bisulphite = HSO3–
- Nitride = N 3–
- Nitrate = NO3–
- Nitrite = NO2–
- Phosphate = PO43-
- Carbonate = CO3– –
- Bicarbonate = HCO3–
- Manganate = MnO4– –
- Permanganate = MnO4–
- Dichromate = Cr2O7– –
- Chromate = CrO4– –
- Cyanide = CN–
- Cyanate = CNO–
- Ferrocyanide = [Fe(CN)6]4-
- Ferricyanide = [Fe(CN)6]3-
Molecular formula
The symbolic representation of a molecule that shows actual number of atoms present in the molecule is called molecular formula.
For example: – HNO3 represents one molecule of Nitric acid.
Writing molecular formula :
Simply apply criss-cross rule.
Eg. i. Sodium sulphate
ii. Ammonium carbonate
iii. Calcium ferrocyanide
Significance of molecular formula :
Qualitative significance :
- Qualitatively formula of molecule represents the name of the substance. For examples: – CaCO3 represent calcium carbonate.
- It also tells the type of elements present in that molecule. For example, CaCO3 contains the element calcium, carbon and oxygen.
Quantitative significance :
Molecular formula of H2SO4 represents its following quantitative significance:-
- One molecule of the sulphuric acid.
- One molecule of sulphuric acid contains two atoms of hydrogen, one atom of sulphur and four atoms of oxygen.
- Molecular weight of the substance is obtained by adding the atomic weight of all the atoms present. Hence, molecular weight of sulphuric acid (H2SO4) is 98.
- The relative weight of the elements presents in the substance is given by the molecular formula. In sulphuric acid molecule, weight ratio of hydrogen, sulphur and oxygen is 2:32:64 or 1:16:32 respectively.
Empirical formula
A formula that gives the simplest whole number ratio of atoms in a compound is called empirical formula.
For example: – Molecular formula of ethane is C2H6 and its empirical formula is CH3. Similarly, the molecular formula of glucose is C6H12O6 and its empirical formula is CH2O.
Name and chemical formula of some common compounds
| General name | Chemical name | Formula |
| water | Dihydrogen monoxide | H2O |
| Common salt/ table salt/ rock salt | Sodium chloride | NaCl |
| Sand/Quartz | Silicon dioxide | SiO2 |
| Marble/Lime Stone | Calcium carbonate | CaCO3 |
| Lime/Quick lime | Calcium Oxide | CaO |
| Washing Soda | Sodium Carbonate | Na2CO3 |
| Caustic Soda | Sodium Hydroxide | NaOH |
| Caustic Potash | Potassium Hydroxide | KOH |
| Baking Powder/backing soda | Sodium bicarbonate | NaHCO3 |
| Paraffins | Alkane | CnH2n+2 |
| Olefins | Alkene | CnH2n |
| Ethylene | Ethene | C2H4 |
| Acetylene | Ethyne | C2H2 |
| Black oxide of copper | Copper(II)oxide | CuO |
| Red oxide of copper | Copper(I)oxide | Cu2O |
| Bleaching Powder | Calcium oxychloride | CaOCl2 |
| Blue vitriol | Copper sulphate pentahydrate | CuSO4.5H2O |
| White vitriol | Zinc sulphate heptahydrate | ZnSO7.7H2O |
| Green vitriol | Ferrous sulphate heptahydrate | FeSO7.7H2O |
| Plaster of Paris | Calcium sulphate semihydrate | CaSO4.1/2H2O or 2CaSO4.H2O |
| Calomel | Mercurous chloride | Hg2Cl2 |
| Dry ice | Solid carbondioxide | CO2 |
| Glucose | Aldohexose | C6H12O6 |
| Laughing gas | Nitrous oxide | N2O |
| Tear gas/chloropicrin | Trichloronitromethane | CCl3.NO2 |
| Sindur (Red lead) /vermilion | Triplumbic tetraoxide | Pb3O4 |
| Urea | Carbamide /amino methanamide | NH2CONH2 |
| Vinegar | Acetic acid | CH3COOH |
| White gold | Platinum | Pt |
Questions and their answers
1. Valency of N in N2O3 is :
a. 1 b. 2
c. 3 d. 4
2. Molecular formula of ferric ferrocyanide is :
a. Fe[Fe(CN)6]3 b. Fe4[Fe(CN)6]3
c. Fe2[Fe(CN)6]3 d. Fe4[Fe(CN)6]
3. Molecular formula of ‘laughing gas’ is :
a. NO2 b. NO
c. N2O3 d. N2O
4. Molecular formula of bleaching powder is :
a. CaSO4 b. CaOCl2
c. CuSO4 d. CHCl3
5. Symbol of element ‘Tin’ is :
a. Sn b. Sb
c. Au d. Ti
6. C6H12O6 is molecular formula of :
a. Glucose b. Fructose
c. Both ‘a’ and ‘b’ d.None of above.
7. Ratio of hydrogen, sulphur and oxygen by weight in a molecule of sulphuric acid is:
a. 1:32:64 b. 2:16:64
c. 2:16:32 d.1:16:32
8. Identify the valency of ‘N’ in N2O, NO, NO2 and N2O5.
9. Write the molecular formula of
- Cupric chloride
- Aluminum sulphate
- Zinc nitrate
- Ferric phosphate
- Ammonium carbonate
- Sodium phosphate
- Potassium ferrocyanide
- Potassium dichromate
- Potassium ferricyanide
- Ammonium cyanate
Answer..
1. – c 2. – b 3.- d(nitrous oxide)
4.- b 5.- a 6.- c 7.– d
8.- 1, 2, 4 and 5
9.- a) CuCl2 b) Al2(SO4)3
c) Zn(NO3)2 d) FePO4
e) (NH4)2CO3 f) Na3PO4
g) K4[Fe(CN)6] h) K2Cr2O7
i) K3[Fe(CN)6] j) NH4CNO
How to recognize a pure substance?
One can identify a pure substance by its characteristics such as viscosity, refractive, index, electrical conductivity, melting point, and density.
A pure substance is defined as a substance that has a fixed composition and fixed properties that cannot be taken away by physical methods. For Pure water freezer at 0° Degree Celsius and boil at 100° Celsius at one atmospheric pressure.
This nature of water same, irrespective of its origin. The Pure Water that is H2 O, has two Hydrogen atoms and one oxygen atom. This composition cannot be changed by physical methods. A pure substance is either an element (Copper) or a compound (Calcium Carbonate).
Element
“An Element is a pure substance that cannot be split into anything simple by physical or chemical methods. –Boyle
“An Element is the basic form of matter that cannot be broken into a simpler substance” – Lavoisier
“An Element is made of the same kind of atom” – Modern Atomic Theory
Examples of elements are Oxygen, Carbon, Iron, Copper, etc. In Oxygen, it has only Oxygen atoms. Similarly, Carbon has only a Carbon atom.
Therefore we can conclude that all the elements are made of one kind of atom only. The atoms of different elements are not similar.
Classification of elements by Physical Properties
The elements can be classified based on the state of the subdivision as Solids, Liquids, and Gases.
Liquid elements are Mercury, Bromine (at room temperature) and Cesium, gallium at (30° C).
Gaseous elements are Hydrogen, Nitrogen, Oxygen, Chlorine, fluorine, Helium, Neon, Argon Krypton, Radon, and Xenon. Solid elements are Carbon, Silicon, Iron, Gold, etc.
Classification of Elements by Properties
Elements can be classified by their properties into Metal, Non-Metals, and Metalloids.
Metals – 70 elements out of 92 elements are metals.
Metals are characterized by:
- Hardness, Shining in appearance (Lustrous).
- Malleability (can be beaten to thin sheets).
- Ductility (can be drawn to long wire)
- Metals are the finest conductors of electricity and heat.
- Example of Metals is Copper, Silver, Gold, etc.
Non-Metal are characterized by:
- Only 16 to 17 elements are non-metals.
- There are soft and non-Lustrous (non-shining)
- Non-Metals are Non-Malleable (cannot be beaten into thin sheets).
- Non-Metals are Non-Ductile ( Cannot be drawn into a thin wire)
- Non-Metals are very bad conductors of heat and electricity.
- Example of Non-Metals is Hydrogen, Oxygen, Sulphur, Carbon etc.
Metalloids are elements that have the property of both metals and non-metals. There are very few metalloids. Examples of Metalloids are Boron, Silicon, Germanium, etc.
Why are Symbols used to represent Chemistry?
It is for Convenience. Every chemical change can be easily represented in the form of a chemical equation. It is difficult to represent the chemical reaction with the full name. So there is a need for the symbol to represent the elements in Chemistry.
What is a Symbol in Chemistry?
A symbol is a short form of the name such as the UK for the United Kingdom, the United States of America as the USA, etc.
In Chemistry, symbols are used to represent the names of elements. The Greece, some earliest symbols are of the form of geometrical shapes used to represent the elements such as Earth, Fire, Air, and Water.
How to write a symbol?
A single letter as a symbol should be written in Capital. Two letters as a symbol, the first letter should be capitalized and the second letter should be small. Importance of the Symbol of an element
Dalton System of Determining Symbols of the Elements:
The Dalton System of Determining Symbols of the Elements refers to an early notation system developed by John Dalton, a British chemist, in the early 19th century. This system was one of the precursors to the modern chemical notation used to represent elements and compounds.
Dalton's system was developed as part of his atomic theory, which proposed that matter is composed of indivisible particles called atoms. He used symbols to represent the different elements and their atomic masses. Here are some key points about Dalton's system:
Symbols: Dalton assigned symbols to elements using a single letter, often the first letter of the element's name. For example, he used "H" for hydrogen, "O" for oxygen, "N" for nitrogen, and so on.
Subscripts: Dalton used subscripts to indicate the relative proportions of atoms in compounds. For example, he represented water as "HO" to indicate one atom of hydrogen and one atom of oxygen. This is quite different from the modern chemical formula for water, which is H₂O, reflecting the fact that water molecules consist of two hydrogen atoms and one oxygen atom.
Atomic Mass: Dalton assigned relative atomic masses to elements based on hydrogen as the reference element. He set the atomic mass of hydrogen to 1 and assigned other elements masses relative to hydrogen. For example, he assigned oxygen an atomic mass of 7 (we now know it's approximately 16).
No Differentiation of Isotopes: Dalton's system did not differentiate between isotopes of the same element. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. This distinction came later with the development of more accurate atomic mass measurements.
It's important to note that Dalton's system was a significant step in the development of chemical notation and atomic theory, but it was eventually refined and replaced by more accurate systems as our understanding of atoms and their behavior grew. The modern periodic table, chemical symbols, and molecular formulas that we use today have evolved from these early concepts and systems.
Most elements, mainly non-metals, use the first letter of their name.
If the elements have the same initial letter as another, then the second letter is taken as its symbol.
If the first two letters of the names of elements are the same, then the first and second or third letter is taken so that the two symbols are not common.
Some symbols are made from the old names or Latin names.
Some elements are named after Country, Scientist, Color, mythological Character, and planets.
The symbol of an element symbolizes:
- Element Name
- One atom of the element
- For Example, the O symbol stands for the element of Oxygen and One atom of Oxygen.
Molecule of Element
A Molecule of an Element contains two or more similar atoms. For example, a Chlorine Molecule has two atoms of Chlorine and it is shown as Cl2 (Chlorine).
And Nitrogen (N2) has two atoms of Nitrogen. Chlorine, Nitrogen, etc have two atoms of the same kind called Diatomic Molecules.
Ozone (O3) consists of three same atoms. Phosphorus (P4) consists of 4 same atoms. Sulphur (S8) has consisted of 8 same atoms.
What is a Compound?
Compounds are formed when two or more elements join together in a fixed ratio by mass.
For example, water (H2O) is formed by a combination of Hydrogen and Oxygen in the ratio of 2:1 by volume or 1:8 by mass.
Element + Element → Compound
N2 + 3H2 →2NH3
2H2 + O2 → 2H2O
Sulphur with oxygen forms colourless gas called Sulphur Dioxide. Sulphur di Oxide gives a pungent smell when heated.
S + O2 → SO2
The greyish liquid formed when Iodine, Aluminum are mixed with water. This compound is called Aluminum Oxide.
2Al + 3I2 → 2 AlI3
The mixture of Iron powder and Sulphur is heated in a test tube. Due to heating, a grey brittle compound is formed which is called Iron Sulphide.
Fe + S → FeS
Characteristics of a Compound
A chemical compound is formed by Chemical, the reaction between two or more elements in a fixed ratio by mass. Every individual element cannot be separated from the compound by physical methods.
A compound is formed when two or more join as a compound associated with the release or absorption of heat. Properties of the elements and the compound formed out of the same elements are different.
A compound is homogenous, and one cannot see the individual element in a compound. The compound is entirely a new thing formed.
Classification of Compound
Inorganic compounds
Those obtained from non-living things such as Rocks, Sand, and Minerals are called Inorganic compounds. An example is Chalk, Marble, Baking Soda, etc.
Organic compounds
The compound is obtained from living sources such as Plants, animals, bacteria, fungi, etc. Examples of organic compounds are proteins, Waxes, Oil, and Carbohydrates.
Uses of Compounds
| Common Name | Chemical Name | Components | Uses |
| Water | Hydrogen Oxide | Hydrogen and Oxygen | Universal Solvent and life source as drinking compound for life on planet earth |
| Table Salt | Sodium Chloride | Sodium and Chlorine | Provides taste for food, prevent dehydration, preservative of vegetable and non-vegetables |
| Sugar | Sucrose | Carbon, Hydrogen, Oxygen | Provides sweetness to food. Also used as a preservative. Eg: Sweets, toffee, fruit juices |
| Baking Soda | Sodium Bi Carbonate | Sodium, Hydrogen, Carbon, and Oxygen | Used in Fire extinguisher, baking powder preparation. Used in Cake and Bread preparation |
| Washing Soda | Sodium Carbonate | Sodium, Carbon, and Oxygen | Cleaning agents such as making of Soaps and Softening of hard water |
| Bleaching Powder | Calcium Oxy Chloride | Calcium, Oxygen, and Chlorine | Used as Bleaching agent, disinfectant, and sterilization of drinking water |
| Quick Lime | calcium oxide | calcium and oxygen | used in the production of glass and cement |
| Slaked Lime | Calcium Hydroxide | calcium, Hydrogen, and oxygen | Whitewashing of walls |
| Lime Stone | Calcium Carbonate | Calcium, Carbon, and Oxygen | Making of Chalk pieces |
Molecule of Compound
The molecule of a compound is one that has two or more different types of atoms.
For example, the molecule of hydrogen chloride contains one atom of hydrogen and one atom of chlorine. Also, Water contains one atom of oxygen and two atoms of hydrogen.
What is a Formula?
A molecule of an element or a compound is represented through a formula. The formula speaks for the number of atoms of each element in the molecule.
Example H2 represents one mole of hydrogen formed by two atoms of hydrogen fused together.
For Water, that is H2O that represents two atoms of hydrogen chemically fused with one atom of oxygen. Note: In H2O, only two atoms of hydrogen are shown, 1 atom of oxygen is not shown. We can conclude that if there is no number as a Subscript, we remember that it is one atom.
What is Valency?
Valency is the ability of an element to combine with others. Oxygen is more likely to combine with Hydrogen than chlorine. Just like some people are friendly with some limited people.
The Hydrogen valency is taken as standard, and other elements’ valency is expressed in terms of hydrogen. The hydrogen atom’s valency is taken as one.
As most of the elements do not merge with hydrogen, the valency of an element is also defined in terms of chlorine or oxygen.
Valency concerning Chlorine
As the valency of chlorine is one, the number of chlorine atoms with which one atom of an element can combine is called its valency.
Valency concerning Oxygen
The valency of oxygen is 2. Double the number of oxygen atoms with which one atom of an element can combine is also called valency. Some element shows more than one valency and is called valence elements.
For example Valency of Iron in FeCl2 is 2. The valency of Iron in FeCl3 is 3. Some elements, mostly rare gases like helium and neon do not merge with other elements and are called Zero Valency.
Some important things in Elements and Compounds
The Air we breathe is not a pure gas it is a mixture of substances. Milk is a liquid mixture of proteins, water, and fat.
“Atom is the smallest particle of an element”.
A molecule is made of the same kind of atoms or different kinds of atoms. Amazon forest produces 20% of the world’s total oxygen. One Once of Gold can be drawn into a thin wire of length of 80km or 50 miles.
The carbon in the human body is enough to fill 9000 lead pencils. The noble gas Xenon lasers can cut things even though diamond-tipped blades cannot cut. The human body contains an average of 250grams of salt.
The metal that has the highest melting point is Tungsten which has 3410° C.
