Periodic table of the elements

Circular periodic table

The periodic table of the elements is a diagrammatic tool to illustrate the scientific theory of periodicity in chemistry, in which the elements have similar properties based on their position on the table. For example, the elements on the left of the table are all metals. The table has a lot of predictive power, although there are many exceptions to the periodic properties.

The periodic table was first developed by Russian chemist Dimitri Mendeleev. Its layout accurately arranges elements by their electron configuration, atomic number, and chemical properties. Using the structure he created, Mendeleev predicted the existence and properties of several yet-undiscovered elements; when those elements were discovered, his estimates proved to be quite accurate, vindicating his theory which had previously been criticized.

Organization

Elements in the periodic table are organized based on the number of electrons in their outermost electron shell. Since farther out shells have more orbitals, this means that there will be more elements in the lower rows of the periodic table than in the higher rows. For example, for [[principle quantum number] n=1, there is only one s-orbital available, which will fit only two electrons (due to the Pauli exclusion principle, which states that no two electrons can have the same quantum numbers). Therefore, only two elements can be in the top row of the periodic table. As the principle quantum number increases, the number of electrons per shell rises, so the farther-down rows hold more elements.

The group number tells how many electrons an element has in its outermost electron shell. For example, every element in group 8A, the Nobel gases, has its outermost electron shell completely full.

External Links

• Interactive Periodic Table You've seen it before, but what do all those symbols and numbers really mean? You're about to find out.
• Name the elements in the Periodic Table!

The Periodic Table

1A																	8A
1 H 1.008	2A											3A	4A	5A	6A	7A	2 He 4.003
3 Li 6.939	4 Be 9.0122											5 B 10.811	6 C 12.011	7 N 14.007	8 O 15.999	9 F 18.998	10 Ne 10.183
11 Na 22.99	12 Mg 24.312	3B	4B	5B	6B	7B	<---	8B	-->	1B	2B	13 Al 26.982	14 Si 28.086	15 P 30.974	16 S 32.064	17 Cl 35.453	18 Ar 39.948
19 K 39.102	20 Ca 40.08	21 Sc 44.956	22 Ti 47.9	23 V 50.942	24 Cr 51.996	25 Mn 54.938	26 Fe 55.847	27 Co 58.933	28 Ni 58.71	29 Cu 63.546	30 Zn 65.37	31 Ga 69.72	32 Ge 72.59	33 As 74.922	34 Se 78.96	35 Br 79.904	36 Kr 83.8
37 Rb 85.47	38 Sr 87.62	39 Y 88.905	40 Zr 91.22	41 Nb 92.906	42 Mo 95.94	43 Tc [97]	44 Ru 101.07	45 Rh 102.91	46 Pd 106.4	47 Ag 107.87	48 Cd 112.4	49 In 114.82	50 Sn 118.69	51 Sb 121.75	52 Te 127.6	53 I 126.9	54 Xe 131.3
55 Cs 132.91	56 Ba 137.34	57* La 138.91	72 Hf 178.49	73 Ta 180.95	74 W 183.85	75 Re 186.2	76 Os 190.2	77 Ir 192.2	78 Pt 195.09	79 Au 196.97	80 Hg 200.59	81 Tl 204.37	82 Pb 207.19	83 Bi 208.98	84 Po 210	85 At 210	86 Rn 222
87 Fr 215	88 Ra 226.03	89** Ac 227.03	104 Rf [261]	105 Db [262]	106 Sg [266]	107 Bh [264]	108 Hs [265]	109 Mt [268]	110 Dt [271]	111 Rg [272]	112   [277]		114   [289]		116   [289]
*Lanthanides		58 Ce 140.12	59 Pr 140.91	60 Nd 144.24	61 Pm 145	62 Sm 150.35	63 Eu 151.96	64 Gd 157.25	65 Tb 158.92	66 Dy 162.5	67 Ho 164.93	68 Er 167.26	69 Tm 168.93	70 Yb 173.04	71 Lu 174.97
**Actinides		90 Th 232.04	91 Pa 231	92 U 238.03	93 Np 237.05	94 Pu 239.05	95 Am 241.06	96 Cm 244.06	97 Bk 249.08	98 Cf 252.08	99 Es 252.08	100 Fm 257.1	101 Md 258.1	102 No 259.1	103 Lr 262.11
	Nonmetals
	Semimetals
	Metals
	Noble Gases