Ar Argon Index

Argon (Ar) Element Properties

Atomic Mass	39.948
Atomic Number	18
Name Origins	Greek, argos = "inactive."
Year Discovered	1894
Discovery Credits	Discovered by Lord Rayleigh (London) and Sir William Ramsay (Bristol), UK
Remarks	Colorless, odorless gas comprising 1 percent of the atmosphere. Used as inert atmosphere in lamps and high temperature metallurgy. Found in potassium-bearing minerals as a trapped gas due to the radioactive decay of K⁴⁰
References	Emsley, J., 1991; THE ELEMENTS : Sec. Ed., Clarendon Press, Oxford, 251 p.
See Also	WebElements, ChemiCool

**Naturally Occurring Isotopes**
Symbol	Isotope Mass	Isotope Nuclide Number	Isotope Number	Natural Abundance	Half-life Units
Ar	35.967545	36	18	0.3370%	Stable
Ar	37.962732	38	18	0.0630%	Stable
Ar	39.962384	40	18	99.6000%	Stable

Group	1	2		3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
Period
1	1 H																		2 He
2	3 Li	4 Be												5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg												13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca		21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr		39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba	*	71 Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra	**	103 Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds
-
*Lanthanides			*	57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb
**Actinides			**	89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No