Periodic Table Long Form (Page 4 of 4) in pdf

several

two and three-

The periodic table has

the conventional table. As long

dimensional periodic

as the medium-long-form prevailed

had some interesting

that subsequent

systems have been

it appeared as though lanthanum

redesigns including as a

atoms resume the

devised in order to

wheel or as these conical

and actinium were equally good

filling of s and p orbitals.

accommodate the transition

candidates for membership to

structures from 1947

And just as Mendeleev solved the

metals in novel ways

group three as were lutetium and

problem by removing his transition

(see above).

lawrencium. But with the growing

elements from the main body of

But there is still nothing drastic

willingness to display the elements in

the table, so modern chemists and

involved in these arrangements,

a long-form table, the choice in favour

physicists solved their problem by

despite their appearance. Tables

of lutetium and lawrencium becomes

removing a block of elements: the

with more significant variations

inescapable. If one places lanthanum

d block. But instead of placing these

place some elements in

and actinium below scandium and

new transition elements to the right

different groups. One such

yttrium in a long-form arrangement

of the main body of the table, they

radical arrangement is the

the sequence of atomic numbers

are traditionally placed between two

left-step periodic table in

is violated in a rather shocking

unevenly separated portions of the

which helium is placed at

manner.

main table, the s block and the p block.

the top of the alkaline earth

Finally, it appears that the

In the 1940s, American chemist

metals rather than at the top

recent synthesis of super-heavy

Glen Seaborg made a further

of the noble gases.

elements up to and including

modification to the periodic table, this

I suggest a table which

element 118, (with the exception

time involving the inner transition

would place hydrogen

of element 117), is reawakening an

elements called the actinides. As a

among the halogens, resulting

interest in how best to represent the

result of his work these elements

in a new perfect atomic number

periodic system.

– which had previously been housed

triad involving hydrogen, fluorine

With the possibly imminent advent

in the main body of the medium-

and chlorine (see below). Triads

of the g-block, formally starting at

long-form table – were also removed

were historically the first hint of

element 121, it will become necessary

to join the lanthanides and to create

a numerical regularity among the

to create a new block in the table.

the long-form periodic table

elements and many people have

Should this be placed as a footnote

(see page 48).

suggested placing hydrogen among

to a long-form table or perhaps

All these forms are still fairly

the halogens on the basis of chemical

incorporated into a very-long-form

traditional, although the act of

and physical evidence.

table with 50 columns? Needless to

One suggestion for a

removing elements from the main

An interesting debate has

say, several versions of both kinds can

reformed table is to

tables does not have to be carried out

developed over which elements

already be found – this is an issue that

place hydrogen with the

on a two-dimensional display. Today,

should be placed in group three of

halogens

won’t be resolved in a hurry.

Eric Scerri teaches chemistry and

history and philosophy of science at

UCLA in Los Angeles, US. He is the

author of The periodic table, its story

and its significance, Oxford University

Press, 2007

References



E R Scerri, Educ. Chem., 2005, 42, 135



E R Scerri, J. Chem. Educ., 2008, 85, 585



W B Jensen, J. Chem. Educ., 1982, 59, 634



Chemistry World

March 2009

Periodic Table Long Form Page 4

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