| Group IA |
IIA | IIIB | IVB | VB | VIB | VIIB | [ | VIII | ] | IB | IIB | IIIA | IVA | VA | VIA | VIIA | VIII | |
| 1 | 1 Hydrogen H 1 |
2 Helium He 4 |
||||||||||||||||
| 2 | 3 Lithium Li 7 |
4 Bery- lium Be 9 |
5 Boron B 11 |
6 Carbon C 12 |
7 Nitrogen N 14 |
8 Oxygen O 16 |
9 Fluorine F 19 |
10 Neon Ne 20 |
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| 3 | 11 Sodium Na 23 |
12 Magnes- ium Mg 24 |
13 Alumin- ium Al 27 |
14 Silicon Si 28 |
15 Phosph- orus P 31 |
16 Suphur S 32 |
17 Chlorine Cl 35 |
18 Argon Ar 40 | ||||||||||
| 4 | 19 Potass- ium K 39 |
20 Calcium Ca 40 |
21 Scand- ium Sc 45 |
22 Titanium Ti 48 |
23 Vanad- ium V 51 |
24 Chrom- ium Cr 52 |
25 Mangan- ese Mn 55 |
26 Iron Fe 56 |
27 Cobalt Co 59 |
28 Nickel Ni 59 |
29 Copper Cu 64 |
30 Zinc Zn 65 |
31 Galium Ga 70 |
32 Germa- nium Ge 73 |
33 Arsenic As 75 |
34 Selen- ium Se 79 |
35 Bromine Br 80 |
36 Krypton Kr 84 |
| 5 | 37 Rubid- ium Rb 85 |
38 Strontium Sr 88 |
39 Ytrium Y 89 |
40 Zircon- ium Zr 91 |
41 Niobium Nb 93 |
42 Molyb- denum Mo 96 |
43 Tech- netium Tc 99 |
44 Ruthe- nium Ru 101 |
45 Rhodium Rh 103 |
46 Pallad- ium Pd 106 |
47 Silver Ag 108 |
48 Cadm- ium Cd 112 |
49 Indium In 115 |
50 Tin Sn 119 |
51 Antim- ony Sb 122 |
52 Tellur- ium Te 128 |
53 Iodine I 127 |
54 Xenon Xe 131 |
| 6 | 55 Cesium Cs 133 |
56 Barium Ba 137 |
57 Lanth- ium * La |
Hafnium Hf 178 |
73 Tantalum Ta 181 |
74 Wolfram- Tungsten W 184 |
75 Rhenium Re 186 |
76 Osmium Os 190 |
77 Iridium Ir 192 |
78 Platinum Pt 195 |
79 Gold Au 197 |
80 Mercury Hg 201 |
81 Thallium Tl 204 |
82 Lead Pb 207 |
83 Bismuth Bi 209 |
84 Polon- ium Po 210 |
85 Astatine At 210 |
86 Radon Rn 222 |
| 7 | 87 Francium Fr 223 |
88 Radium Ra 226 |
89 Actinium * Ac 227 |
Kurcha- tovium Ku |
105 Dubnium Db |
106 Seaborg- ium Sg |
107 Bohrium Bh |
108 Hassium Hs |
109 Meitner- ium Mt |
110 Darmstad- ium Ds |
111 Roent- genium Rg |
112 Copernic- ium Cn |
<--Atomic Number
<--Name <--Symbol <--Approximate atomic weight |
|||||
| Lanthanide Series * | 6 | 58 Curium Ce 140 |
59 Praseod- ymium Pr 141 |
60 Neod- ymium Nd 144 |
61 Prome- thium Pm 147 |
62 Samar- ium Sm 150 |
63 Europium Eu 152 |
64 Gadol- inium Gd 157 |
65 Terbium Tb |
66 Dyspro- sium Dy 163 |
67 Holmium Ho 165 |
68 Erbium Er 167 |
69 Thulium Tm 169 |
70 Ytter- bium Yb 173 |
71 Lutet- ium Lu 175 |
| Actinide Series * | 7 | 90 Thorium Th 232 |
91 Proact- inium Pa 231 |
92 Uranium U 238 |
93 Neptun- ium Np 237 |
94 Pluton- ium Pu 242 |
95 Ameri- cium Am 243 |
96 Cerium Cm 247 |
97 Berkel- ium Bk 247 |
98 Califo- nium Cf 251 |
99 Einste- nium Es 254 |
100 Fermium Fm 253 |
101 Mendel- ivium Md 256 |
102 Nobel- ium No 254 |
103 Lawren- cium Lr 257 |
| Work
on the atomic weights of elements was first published in 1828 by the Swedish chemist Berzelius.
Berzelius suggested that the initial letter of the Latin name (or initial letter plus second letter) could be used as a symbol. Therefore, oxygen could be O, nitrogen N, hydrogen H, calcium Ca, chlorine Cl, copper(cuprum) Cu, gold(aurum) Au, and so on. The makeup of compounds could then be expressed with letters, together with numerical subscripts, where more than one atom was present in the molecule. Thus, ammonia could be NH3, calcium carbonate CaCO3, salt NaCl, water H²O and so on. Berzelius is also credited with the discovery of the elements selenium, silicon and thorium. In 1852, Sir Edward Frankland, an English chemist, devised the theory of valence, which describes the fixed capacity of types of atoms to combine with other atoms. This theory was further advanced by Kekulé, a German chemist, to describe the bonding of atoms in different ways, and to provide an explanation for the existence of isomers (compounds with the same atoms and valences, but arranged differently). Like other chemists before himself, Mendeléev, a Russian chemist, tried to arrange the known elements (there were sixty-three at that time) in order of atomic weight. Mendeléev found he could arrange the elements in such a way as to get periodic rises and falls of valences. He could also arrange them in rows, so that the elements with similar valence would all fall into a vertical column, giving rise to a table of elements and properties. These elements also showed trends of similarity along rows and columns in chemical properties. Because of the periodic rises and falls in valence and the equally periodic repetitions of properties in the rows, this table of elements is called a periodic table. When he published his first table in 1869, Mendeléev left gaps in the table in order to make the missing elements would fit into the proper columns and announced that the gaps represented elements not yet discovered. This prediction was met with considerable skepticism, but when Lecoq de Boisbaudran discovered gallium in 1874, which matched up with the predicted table of elements, Mendeléev was vindicated. The search for the missing elements was intensified and two more elements, scandium and germanium, were found in quick succession. Mendeléev's accomplishment was celebrated and he became the most famous chemist in the world in the 1870's. In 1955, a newly-discovered element (no 101, part of the Actinide series), was named mendelevium, in belated recognition of Mendeleev's importance in the study of the elements. |
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