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In the standard Periodic Table layout , all the elements up to 56 are in order i.e are in the same layout table. However, lanthanides and actinides are always shown separately from the layout like in this layout: enter image description here

What is the reason behind this structure?

Is this standard layout or can I represent it like this too? enter image description here

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7 Answers 7

up vote 9 down vote accepted

The Periodic Table arranges elements in blocks as each type of orbital fills with electrons - $s,p,d,f,g,h$. Alkali metals and alkaline earths are $s$-block filling (but could be one $s$-block slot). $p$-block six electrons to fill are trelides, tetralides, pnticides, chalcogenides, halides, inert gases (but could be one $p$-block slot). Transition metal $d$-block is ten elements (but could be one $d$-block slot). Filling the $f$-block are 14 elements, lanthanoids and actinoids. That gets sloppy to print and the elements are (or at least were) overall obscure. They get condensed.

Representing the Periodic Table has become an an art form. The plain vanilla variety is terse and useful.

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One of my science teachers told me that the only reason that they put away the lanthanides and actinides in a separate row was because it would mess up the order and like shape and structure and some rules and stuff... so does that mean my teacher told be BS? –  PhyCS Sep 19 at 20:57

Because if you put lanthanides and actinides in to the Periodic Table like transition metals, the table will be way too wide.

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The two rows of elements present at the bottom of the periodic table are called the 4f series or lanthanoids and 5f or actanoids. They are also called inner transition elements. With each series, the properties of component elements closely resembles each other so their chemistry becomes complicated than their corresponding lanthanoids. Actanoids have large number of oxidation states compared to lanthanoids. Actanoid are radioactive and are man-made in the laboratory. They are not completely studied. Hence they are placed separately in the periodic table.

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Welcome to chemistry.SE! If you had any questions about the policies of our community, you can ‎visit the help center or take a ‎‎tour of the website.‎ –  inɒzɘmɒЯ.A.M Feb 23 at 18:07

Also the actinides and lanthanides have very similar chemical behaviour- I think nearly all have a possible +3 oxidation state and similar metallurgical behaviour. For a long time, lanthanides was added as mishmetal to steel alloys.

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There is no scientific reason not to put the f-blocks between s- and d-blocks!

However, doing so will create a very wide periodic table: The s-, p- and d-block are 18 elements wide, the f-block would add another 14, so almost double the width. Therefore, it is customary to save space and put the f-block at the bottom separately. It is not mandatory, e.g. Wikipedia uses the fully horizontal layout on element pages.

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So there is a reason - it looks better and fits better into most spaces. –  bon Sep 19 at 18:19
@bon Do you agree more with me adding the word ‘scientific’? ;) –  Jan Sep 19 at 20:32
Oh go on then ;) –  bon Sep 19 at 21:19

To preserve symmetry shape lanthanides are placed below main table .actually vertical elements are similar and horizontal elements are dis similar .but lanthanides shows horizontal chemical similarities so placed in f block

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Welcome to chem.SE. As I don't think you're referring to molecular symmetry, your answer seems a bit vague to me. It's better if you clarify your points and provide more examples. –  inɒzɘmɒЯ.A.M Jun 19 at 17:49

The Schrodinger equation allows you to essentially derive the "shape" of the entire periodic table. How you place the elements really doesn't mean anything, it's just a map on paper of the territory, which is really the (not so simple) fact of how electrons stack up onto increasingly larger numbers of protons concentrated in one spot.

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