Matter is classified into solids, liquids and gases. Matter can also be classified into elements, compounds and mixtures based on composition Fe, Ag,

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1 Matter is classified into solids, liquids and gases. Matter can also be classified into elements, compounds and mixtures based on composition Fe, Ag, Au, Cu, Iron element is made of iron atoms. Silver element is made of silver atoms.

2 Elements are the pure substances containing only one kind atoms, which cannot be decomposed by any physical or chemical process.

3 All matter is composed of small particles called atoms. Atom is made of smaller particles (sub atomic particles) are called the fundamental particles.

4 The number of subatomic particles known is very large. For us, the three most important are the proton, neutron and electron. It is a fascinating story that these. Fundamental particles go to make the internal structure of the atom.

5 Chemists have discovered 118 elements so far. Among these elements, 92 are normal elements and remaining are synthetic elements.

6 1. An element is a pure substance, made up of only one kind of atoms 2. An atom is smallest particle of an element and it possesses properties of that element 3. Elements may occur in the free state in nature or found in the form of their compounds.

7 Eg:- Iron FeS, Fe 2 O 3, Fe 3 O 4, Ag, Au Native form Cu CuFeS 2 Some elements (like radioactive elements) can be prepared artificially by nuclear reaction. eg: 88 Ra Rn He 4 Radium Radon

8 The properties of different elements are different. This is because, the arrangement of electrons (electronic configuration) in atoms are different. Li F He Na Cl Ne K Br Kr

9 Need for classification of elements During 17 th century, only few elements were known. Later on many elements were discovered in nature, the number of elements in the list of known elements went on increasing. It was thought that elements must be properly classified in order to make a systematic study of elements, otherwise it becomes impossible to understand the properties of elements.

10 Advantages of classification of elements. i) To study the elements in a systematic manner. ii) To correlate the properties of elements. (Eg: H 2 0, HNO 3, HCl] iii) To know the type of different elements, compounds from that different elements can form.

11 Historical background of classification of elements : Earlier, an attempt was made to classify the elements into metals and non-metals.

12 Metals An element is a metal if it has the following properties 1. It is lustrous i.e., it has shining surface. 2. It is a good conductor of heat and electricity. 3. It is ductile i.e.,it can be drawn into wires. 4. It is malleable i.e., it can be beaten into thin sheets. 5. It is solid at room temperature. 6. It has a tendency to lose one or more electrons.

13 Exceptions: Mercury and Gallium are liquids at room temperature. Zinc is not malleable and ductile. Sl N Name in English Name in other language Symbol 1 Lithium - Li 2 Sodium Natrium (latin) Na 3 Magnesium Mg 4 Aluminium Al 5 Potassium Kalium ( Latin) K 6 Calcium Ca 7 Vanadium V

14 8 Chromium Cr 9 Manganese Mn 10 Iron Errum ( Latin) Fe 11 Cobalt Co 12 Nickel Ni 13 Copper Cuprum (Latin) Cu 14 Zinc Zn 15 Gallium Ga 16 Silver Argentums (Latin) Ag 17 Tin Stannum (latin) Sn 18 Barium - Ba 19 Platinum - Pt 20 Gold Aurum (Latin) Au 21 Mercury Hydrargyrum (Latin) Hg 22 Lead Plambun (latin) Ph 23 Radium - Rq 24 Uranium Wolram (German) U 25 Tungsten - W 26 Thorium - Th

15 Johann Wolfgang Döbereiner ( ) Döbereiner grouped elements to show that atomic weights of a middle element were an average of two similar elements.

16 Examples of Döbereiner Triads: the atomic weight of bromine might be the arithmetical mean of the atomic weights of chlorine and iodine. This mean is ( )/2 = This number is not much greater than that found by Berzelius (78.383) Using modern values: Cl = Br = I =

17 In the alkali group, soda stands in the middle Using modern values: Li = 6.94 Na = K = Atm. of Li + Atm.of K Atm. of Na=

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20 Periodic Law The properties of elements are a periodic function of their atomic number P = F(z)

21 Periodic Law When elements are arranged in order of atomic number, similar properties recur periodically. Atomic radii vs. Z K Na Li

22 First Ionization Energy Atomic number

23 Chemical and Physical properties Type of Bonding and structure Atomic properties Atomic number

24 First I.E. Variations: 1. Across a period 2. Down the group He Ne Ar N F P Be H C O Mg Si S Cl Ca B Li Na Al K Atomic number

25 K Na Ca Li Mg Be H He Ne Ar

26 H 37 He 54 Li 156 Be 105 B 91 C 77 N 71 O 60 F 67 Ne 80 Na 186 Mg 160 Al 143 Si 117 P 111 S 104 Cl 99 Ar 96 K 231 Ca 197 Sc 161 Ti 154 V 131 Cr 125 Mn 118 Fe 125 Co 125 Ni 124 Cu 128 Zn 133 Ga 123 Ge 122 As 116 Se 115 Br 114 Kr 99 Rb 243 Sr 215 Y 180 Zr 161 Nb 147 Mo 136 Tc 135 Ru 132 Rh 132 Pd 138 Ag 144 Cd 149 In 151 Sn 140 Sb 145 Te 139 I 138 Xe 109 Cs 265 Ba 210 Hf 154 Ta 143 W 137 Re 138 Os 134 Ir 136 Pt 139 Au 144 Hg 147 Tl 189 Pb 175 Bi 155 Po 167 At 145 Rn La 187 Ce 183 Pr 182 Nd 181 Pm 181 Sm 180 Eu 199 Gd 179 Tb 176 Dy 175 Ho 174 Er 173 Tm 173 Yb 194 Lu 172 Atomic Radius (pm) 1pm=1x10-12 m

27 H F Cl Li Na He Ne Ar Atomic number K Ca Electronegativity

28 Increase in electronegativity Decrease H 2.1 He - Li 1.0 Be 1.5 B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Ne - Na 0.9 Mg 1.2 Al 1.5 Si 1.8 P 2.1 S 2.5 Cl 3.0 Ar - K 0.8 Al 1.0