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The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table, , Journal of Chemical Education, 08/1982, Volume 59, Issue 8, p.634-636, (1982)

The Periodic Table: Its Story and Its Significance by Eric Scerri

Periods in the periodic table

There are 7 periods in the standard form of the periodic table:

• Period 1
• Period 2
• Period 3
• Period 4
• Period 5
• Period 6
• Period 7

Period Number

In the standard form of the periodic table the s-block, p-block, and d-block elements are organised into horizontal rows called periods. In WebElements these are labelled from 1 to 7.

The f-block

The f-block elements are assigned to Periods 6 (lanthanoids) and 7 (actinoids) since that is where they are located in the full, or extended, version of the periodic table.

The Mendeleev Periodic Table

This table shows the form of Mendeleev's Periodic Table of the chemical elements as published in 1872. The heading "Reihen" means "Row" and the heading "Gruppe" means "Group". The symbols R²O and RH⁴, etc., are written in the style of the time which uses superscripts to denote the number of atoms in molecules rather than the current style which uses subscripts. The gaps marked with hyphens ("-") represent chemical elements deduced by Mendeleev as existing but unknown in 1872. He was able to predict with considerable success the properties of some of the missing chemical elements such as germanium.

Reihen	Gruppe I. - R2O	Gruppe II. - RO	Gruppe III. - R2O3	Gruppe IV. RH4 RO2	Gruppe V. RH3 R2O5	Gruppe VI. RH2 RO3	Gruppe VII. RH R2O7	Gruppe VIII. - RO4
1	H=1
2	Li=7	Be=9,4	B=11	C=12	N=14	O=16	F=19
3	Na=23	Mg=24	Al=27,3	Si=28	P=31	S=32	Cl=35,5
4	K=39	Ca=40	-=44	Ti=48	V=51	Cr=52	Mn=55	Fe=56, Ce=59, Ni=59, Cu=63.
5	(Cu=63)	Zn=65	-=68	-=72	As=75	Se=78	Br=80
6	Rb=85	Sr=87	?Yt=88	Zr=90	Nb=94	Mo=96	-=100	Ru=104, Rh=104, Pd=106, Ag=108.
7	(Ag=108)	Cd=112	In=113	Sn=118	Sb=122	Te=125	J=127
8	Cs=133	Ba=137	?Di=138	?Ce=140	-	-	-	- - - -
9	(-)	-	-	-	-	-	-
10	-	-	?Er=178	?La=180	Ta=182	W=184	-	Os=195, Ir=197, Pt=198, Au=199
11	(Au=199)	Hg=200	Tl=204	Pb=207	Bi=208	-	-
12	-	-	-	Th=231	-	U=240	-	- - - -

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The positions of the elements La, Ac, Lu, and Lr in the WebElements periodic table is justified eloquently in the article by William B. Jensen.1 in J. Chem. Ed..

Elements 117 is not known at the time of writing, but are shown "greyed-out" in the tables at their expected positions for information.

• 1. The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table,
  
  , Journal of Chemical Education, 08/1982, Volume 59, Issue 8, p.634-636, (1982)
  

The Janet periodic table

The Janet periodic table is an excellent alternative periodic table and organises elements according to orbital filling. Therefore, hydrogen is above lithium on the grounds they are both ns¹, and helium above beryllium on the grounds they are both ns². Current Group numbers are displayed to help orientation with the standard table.

The JANET periodic table.

Group															3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	1	2
Period
1																															1 H	2 He
1																															3 Li	4 Be
2																									5 B	6 C	7 N	8 O	9 F	10 Ne	11 Na	12 Mg
3																									13 Al	14 Si	15 P	16 S	17 Cl	18 Ar	19 K	20 Ca
4															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	37 Rb	38 Sr
5															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	55 Cs	56 Ba
6	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	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	87 Fr	88 Ra
7	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	103 Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds	111 Rg	112 Cp	113 Uut	114 Uuq	115 Uup	116 Uuh	117 Uus	118 Uuo	119 Uue	120 Ubn

The Mendeleev Periodic Table

This table shows the form of Mendeleev's Periodic Table of the chemical elements as published in 1872. The heading "Reihen" means "Row" and the heading "Gruppe" means "Group". The symbols R²O and RH⁴, etc., are written in the style of the time which uses superscripts to denote the number of atoms in molecules rather than the current style which uses subscripts. The gaps marked with hyphens ("-") represent chemical elements deduced by Mendeleev as existing but unknown in 1872. He was able to predict with considerable success the properties of some of the missing chemical elements such as germanium.

Reihen	Gruppe I. - R2O	Gruppe II. - RO	Gruppe III. - R2O3	Gruppe IV. RH4 RO2	Gruppe V. RH3 R2O5	Gruppe VI. RH2 RO3	Gruppe VII. RH R2O7	Gruppe VIII. - RO4
1	H=1
2	Li=7	Be=9,4	B=11	C=12	N=14	O=16	F=19
3	Na=23	Mg=24	Al=27,3	Si=28	P=31	S=32	Cl=35,5
4	K=39	Ca=40	-=44	Ti=48	V=51	Cr=52	Mn=55	Fe=56, Ce=59, Ni=59, Cu=63.
5	(Cu=63)	Zn=65	-=68	-=72	As=75	Se=78	Br=80
6	Rb=85	Sr=87	?Yt=88	Zr=90	Nb=94	Mo=96	-=100	Ru=104, Rh=104, Pd=106, Ag=108.
7	(Ag=108)	Cd=112	In=113	Sn=118	Sb=122	Te=125	J=127
8	Cs=133	Ba=137	?Di=138	?Ce=140	-	-	-	- - - -
9	(-)	-	-	-	-	-	-
10	-	-	?Er=178	?La=180	Ta=182	W=184	-	Os=195, Ir=197, Pt=198, Au=199
11	(Au=199)	Hg=200	Tl=204	Pb=207	Bi=208	-	-
12	-	-	-	Th=231	-	U=240	-	- - - -