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The table is useful for modern students and scientists because it helps predict thetypes of chemical reactions that are likely for an element. Rather than memorizefacts and figures for each element, a quick glance at the table reveals a lot about

the reactivity of an element, whether it is likely to conduct electricity, whether itis hard or soft, and many other characteristics.

Elements in the same column as each other (groups share similar properties. !ore"ample, the elements in the first column (the alkali metals are all metals thatusually carry a #$ charge in reactions, react vigorously with water, and combinereadily with nonmetals.

Elements in the same row as each other (periods share highest une"citedelectron energy level.

%nother useful feature of the periodic table is that most table provide all theinformation you need to balance chemical reactions at a glance. The table tells anelements atomic number and usually its atomic weight. The usual charge on anelement is indicated by an element&s group.

Use• 'hemists use the periodic table to organize and study elements found in the world.

The table gives them basic information regarding each known element, in blocks. Each block of the periodic table consists of specific information pertaining to an element. There isthe element&s atomic symbol (such as for boron . There is its atomic number above thesymbol (in boron&s case, ) and its atomic mass below the symbol (in boron&s case, #*.+# .The atomic symbol is one or two letters that represent the element. That atomic number isthe number of protons in one atom of the element, which in turn characterizes the element&schemical behavior. %n element&s atomic mass is the total mass of protons, neutrons andelectrons in a single atom of the element.

Using the data in the table scientists, students, and others that are familiar with the periodic table can extractinformation concerning individual elements. For instance, a scientist can use carbon's atomic mass todetermine how many carbon atoms there are in a 1 kilogram block of carbon.

People also gain information from the periodic table by looking at how it is put together . y examining anelement's position on the periodic table, one can infer the electron configuration. !lements that lie in the samecolumn on the periodic table "called a #group#$ have identical valance electron configurations and conse%uentlybehave in a similar fashion chemically. For instance, all the group 1& elements are inert gases. he periodic

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table contains an enormous amount of important information. People familiar with how the table is put togethercan %uickly determine a significant amount of information about an element.

To summarize, the periodic table is important because it is organized to provide alot of information about elements and how they relate to each other in one easyto use reference-

#. The table can be used to predict properties of elements, even those thathave not been discovered.

. 'olumns (groups and rows (periods indicate elements that share similarcharacteristics.

/. The table makes trends in element properties apparent.

0. The table provides important information used to balance chemicalequations.

A BRIEF HISTORY OF THE DEVELOPMENT OF PERIODICTABLE

Although Dmitri Me !elee" is o#te $o si!ere! the %#&ther% o# the 'erio!i$ t&(le) the*or+ o# m& , s$ie tists $o tri(ute! to its 'rese t #orm-

In the Beginning

A e$ess&r, 'rere.uisite to the $o stru$tio o# the 'erio!i$ t&(le *&s the !is$o"er, o#the i !i"i!u&l eleme ts- Although eleme ts su$h &s gol!) sil"er) ti ) $o''er) le&! & !

mer$ur, h&"e (ee + o* si $e & ti.uit,) the #irst s$ie ti#i$ !is$o"er, o# & eleme to$$urre! i /012 *he He ig Br& ! !is$o"ere! 'hos'horous- Duri g the e3t 455,e&rs) & "&st (o!, o# + o*le!ge $o $er i g the 'ro'erties o# eleme ts & ! their$om'ou !s *&s &$.uire! (, $hemists 6 "ie* & /725 &rti$le o the eleme ts8- B, /902)& tot&l o# 0: eleme ts h&! (ee !is$o"ere!- As the um(er o# + o* eleme ts gre*)s$ie tists (eg& to re$og i;e '&tter s i 'ro'erties & ! (eg& to !e"elo' $l&ssi#i$&tios$hemes-

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Law of Triads

I /9/7 <oh& Do(erei er oti$e! th&t the &tomi$ *eight o# stro tium #ell mi!*&, (et*ee the *eights o# $&l$ium & ! (&rium) eleme ts 'ossessi g simil&r $hemi$&l 'ro'erties- I /942) &#ter !is$o"eri g the h&loge tri&! $om'ose! o# $hlori e) (romi e) & ! io!i e & ! the &l+&li met&l tri&! o# lithium) so!ium & ! 'ot&ssium he 'ro'ose! th&t &ture $o t&i e! tri&!s o# eleme ts the mi!!le eleme t h&! 'ro'ertiesth&t *ere & &"er&ge o# the other t*o mem(ers *he or!ere! (, the &tomi$ *eight6the L&* o# Tri&!s8-

This e* i!e& o# tri&!s (e$&me & 'o'ul&r &re& o# stu!,- Bet*ee /942 & ! /9=9 &um(er o# s$ie tists 6<e& B&'tiste Dum&s) Leo'ol! >meli ) Er st Le sse ) M&3 "o

Pette +o#er) & ! <-P- Coo+e8 #ou ! th&t these t,'es o# $hemi$&l rel&tio shi's e3te !e! (e,o ! the tri&!- Duri g this time #luori e *&s &!!e! to the h&loge grou'? o3,ge )sul#ur)sele ium & ! tellurium *ere grou'e! i to & #&mil, *hile itroge ) 'hos'horus)&rse i$) & timo ,) & ! (ismuth *ere $l&ssi#ie! &s & other- U #ortu &tel,) rese&r$h ithis &re& *&s h&m'ere! (, the #&$t th&t &$$ur&te "&lues o# *ere ot &l*&,s &"&il&(le-

First Attempts At Designing a Periodic Table

I# & 'erio!i$ t&(le is reg&r!e! &s & or!eri g o# the $hemi$&l eleme ts !emo str&ti gthe 'erio!i$it, o# $hemi$&l & ! 'h,si$&l 'ro'erties) $re!it #or the #irst 'erio!i$ t&(le6'u(lishe! i /9048 'ro(&(l, shoul! (e gi"e to & Fre $h geologist) A-E-Begu,er !eCh& $ourtois- De Ch& $ourtois tr& s$ri(e! & list o# the eleme ts 'ositio e! o &$,li !er i terms o# i $re&si g &tomi$ *eight- @he the $,li !er *&s $o stru$te! soth&t /0 m&ss u its $oul! (e *ritte o the $,li !er 'er tur ) $losel, rel&te! eleme ts*ere li e! u' "erti$&ll,- This le! !e Ch& $ourtois to 'ro'ose th&t %the 'ro'erties o#the eleme ts &re the 'ro'erties o# um(ers-% De Ch& $ourtois *&s #irst to re$og i;eth&t eleme t&l 'ro'erties reo$$ur e"er, se"e eleme ts) & ! usi g this $h&rt) he *&s&(le to 're!i$t the stoi$hiometr, o# se"er&l met&lli$ o3i!es- U #ortu &tel,) his $h&rti $lu!e! some io s & ! $om'ou !s i &!!itio to eleme ts-

Law of Octaves

<oh Ne*l& !s ) & E glish $hemist) *rote & '&'er i /90: *hi$h $l&ssi#ie! the =0est&(lishe! eleme ts i to // grou's (&se! o simil&r 'h,si$&l 'ro'erties) oti g th&tm& , '&irs o# simil&r eleme ts e3iste! *hi$h !i##ere! (, some multi'le o# eight i&tomi$ *eight- I /901 Ne*l& !s 'u(lishe! his "ersio o# the 'erio!i$ t&(le & !

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'ro'ose! the L&* o# O$t&"es 6(, & &log, *ith the se"e i ter"&ls o# the musi$&ls$&le8- This l&* st&te! th&t & , gi"e eleme t *ill e3hi(it & &logous (eh&"ior to theeighth eleme t #ollo*i g it i the t&(le-

Who Is The Father of the Periodic Table?

There h&s (ee some !is&greeme t &(out *ho !eser"es $re!it #or (ei g the %#&ther% o# the 'erio!i$ t&(le) the >erm& Loth&r Me,er 6'i$ture! here8 or the Russi& DmitriMe !elee"- Both $hemists 'ro!u$e! rem&r+&(l, simil&r results &t the s&me time*or+i g i !e'e !e tl, o# o e & other- Me,er s /901 te3t(oo+ i $lu!e! & r&ther&((re"i&te! "ersio o# & 'erio!i$ t&(le use! to $l&ssi#, the eleme ts- This $o siste! o#&(out h&l# o# the + o* eleme ts liste! i or!er o# their &tomi$ *eight & !!emo str&te! 'erio!i$ "&le $e $h&ges &s & #u $tio o# &tomi$ *eight- I /909) Me,er$o stru$te! & e3te !e! t&(le *hi$h he g&"e to & $olle&gue #or e"&lu&tio -U #ortu &tel, #or Me,er) Me !elee" s t&(le (e$&me &"&il&(le to the s$ie ti#i$

$ommu it, "i& 'u(li$&tio 6/9028 (e#ore Me,er s &''e&re! 6/9758-

Dmitri I"& o"i$h Me !elee" 6/9:1 /2578) the ,ou gest o# /7$hil!re *&s (or i the Si(eri& to* o# To(ol s+ *here his #&ther*&s & te&$her o# Russi& liter&ture & ! 'hiloso'h, 6'ortr&it (, Il,i&Re'i 8- Me !elee" *&s ot $o si!ere! & outst& !i g stu!e t i his

e&rl, e!u$&tio '&rtl, !ue to his !isli+e o# the $l&ssi$&l l& gu&ges th&t *ere &im'ort& t e!u$&tio &l re.uireme t &t the time e"e though he sho*e! 'ro*ess im&them&ti$s & ! s$ie $e- A#ter his #&ther s !e&th) he & ! his mother mo"e! to St-Peters(urg to 'ursue & u i"ersit, e!u$&tio - A#ter (ei g !e ie! &!missio to (oth theU i"ersit, o# Mos$o* & ! St- Peters(urg U i"ersit, (e$&use o# his 'ro"i $i&l

(&$+grou ! & ! u e3$e'tio &l &$&!emi$ (&$+grou !) he #i &ll, e&r e! & 'l&$e &t theM&i Pe!&gogi$&l I stitute 6St- Peters(urg I stitute8- U'o gr&!u&tio ) Me !elee"too+ & 'ositio te&$hi g s$ie $e i & g,m &sium- A#ter & time &s & te&$her) he *&s&!mitte! to gr&!u&te *or+ &t St- Peters(urg U i"ersit, *here he e&r e! & M&ster s!egree i /9=0- Me !elee" so im'resse! his i stru$tors th&t he *&s ret&i e! to le$turei $hemistr,- A#ter s'e !i g /9=2 & ! /905 i >erm& , #urtheri g his $hemi$&lstu!ies) he se$ure! & 'ositio &s 'ro#essor o# $hemistr, &t St- Peters(urg U i"ersit,) &

'ositio he ret&i e! u til /925- @hile *riti g & te3t(oo+ o s,stem&ti$ i org& i$$hemistr,) Principles of Chemistry ) *hi$h &''e&re! i thirtee e!itio s the l&st (ei gi /217) Me !elee" org& i;e! his m&teri&l i terms o# the #&milies o# the + o*eleme ts *hi$h !is'l&,e! simil&r 'ro'erties- The #irst '&rt o# the te3t *&s !e"ote! tothe *ell + o* $hemistr, o# the h&loge s- Ne3t) he $hose to $o"er the $hemistr, o#the met&lli$ eleme ts i or!er o# $om(i i g 'o*er &l+&li met&ls #irst 6$om(i i g

'o*er o# o e8) &l+&li e e&rths 6t*o8) et$- Ho*e"er) it *&s !i##i$ult to $l&ssi#, met&ls

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su$h &s $o''er & ! mer$ur, *hi$h h&! multi'le $om(i i g 'o*ers) sometimes o e& ! other times t*o- @hile tr,ui g to sort out this !ilem&) Me !elee" oti$e! '&tter si the 'ro'erties & ! &tomi$ *eights o# h&loge s) &l+&li met&ls & ! &l+&li e met&ls- Heo(ser"e! simil&rities (et*ee the series Cl C& ) Br R( Sr & ! I Cs B&- I & e##ortto e3te ! this '&tter to other eleme ts) he $re&te! & $&r! #or e&$h o# the 0: + o*eleme ts- E&$h $&r! $o t&i e! the eleme t s s,m(ol) &tomi$ *eight & ! its$h&r&$teristi$ $hemi$&l & ! 'h,si$&l 'ro'erties- @he Me !elee" &rr& ge! the $&r!so & t&(le i or!er o# &s$e !i g &tomi$ *eight grou'i g eleme ts o# simil&r 'ro'ertiestogether i & m& er ot u li+e the $&r! &rr& geme t i his #&"orite solit&re $&r!g&me) '&tie $e) the 'erio!i$ t&(le *&s #orme!- From this t&(le) Me !elee" !e"elo'e!his st&teme t o# the 'erio!i$ l&* & ! 'u(lishe! his *or+ On the Relationship of the

Properties of the Elements to their Atomic Weights i /902- The &!"& t&ge o#Me !elee" s t&(le o"er 're"ious &ttem'ts *&s th&t it e3hi(ite! simil&rities ot o l, ism&ll u its su$h &s the tri&!s) (ut sho*e! simil&rities i & e tire et*or+ o# "erti$&l)hori;o t&l) & ! !i&go &l rel&tio shi's- I /250) Me !elee" $&me *ithi o e "ote o#

(ei g &*&r!e! the No(el Pri;e #or his *or+-

At the time th&t Me !elee" !e"elo'e! his 'erio!i$ t&(le si $e the e3'erime t&ll,!etermi e! &tomi$ m&sses *ere ot &l*&,s &$$ur&te) he reor!ere! eleme ts !es'itetheir &$$e'te! m&sses- For e3&m'le) he $h& ge! the *eight o# (er,llium #rom /1 to 2-This 'l&$e! (er,llium i to >rou' 4 &(o"e m&g esium *hose 'ro'erties it more$losel, resem(le! th& *here it h&! (ee lo$&te! &(o"e itroge - I &ll Me !elee"#ou ! th&t /7 eleme ts h&! to (e mo"e! to e* 'ositio s #rom those i !i$&te! stri$tl,

(, &tomi$ *eight #or their 'ro'erties to $orrel&te *ith other eleme ts- These $h& ges

i !i$&te! th&t there *ere errors i the &$$e'te! &tomi$ *eights o# some eleme ts6&tomi$ *eights *ere $&l$ul&te! #rom $om(i i g *eights) the *eight o# & eleme tth&t $om(i es *ith & gi"e *eight o# & st& !&r!-8 Ho*e"er) e"e &#ter $orre$tio s*ere m&!e (, re!etermi i g &tomi$ *eights) some eleme ts still ee!e! to (e 'l&$e!out o# or!er o# their &tomi$ *eights- From the g&'s 'rese t i his t&(le) Me !elee"

're!i$te! the e3iste $e & ! 'ro'erties o# u + o* eleme ts *hi$h he $&lle! e+&&lumi um) e+& (oro ) & ! e+& sili$o - The eleme ts g&llium) s$& !ium & !germ& ium *ere #ou ! l&ter to #it his 're!i$tio s .uite *ell- I &!!itio to the #&$tth&t Me !elee" s t&(le *&s 'u(lishe! (e#ore Me,ers ) his *or+ *&s more e3te si"e

're!i$ti g e* or missi g eleme ts- I &ll Me !elee" 're!i$te! the e3iste $e o# /5

e* eleme ts) o# *hi$h se"e *ere e"e tu&ll, !is$o"ere! the other three) &tomi$*eights 1=) /10 & ! /7= !o ot e3ist- He &lso *&s i $orre$t i suggesti g th&t theeleme t '&irs o# &rgo 'ot&ssium) $o(&lt i$+el & ! tellurium io!i e shoul! (ei ter$h& ge! i 'ositio !ue to i &$$ur&te &tomi$ *eights- Although these eleme ts!i! ee! to (e i ter$h& ge!) it *&s (e$&use o# & #l&* i the re&so i g th&t 'erio!i$it,is & #u $tio o# &tomi$ *eight-

Discover of the !oble "ases

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I /92= Lor! R&,leigh re'orte! the !is$o"er, o# & e* g&seouseleme t &me! &rgo *hi$h 'ro"e! to (e $hemi$&ll, i ert- Thiseleme t !i! ot #it & , o# the + o* 'erio!i$ grou's- I/929) @illi&m R&mse, suggeste! th&t &rgo (e 'l&$e! i to the

'erio!i$ t&(le (et*ee $hlori e & ! 'ot&ssium i & #&mil, *ithhelium) !es'ite the #&$t th&t &rgo s &tomi$ *eight *&s gre&ter th& th&t o# 'ot&ssium- This grou' *&s terme! the %;ero% grou'!ue to the ;ero "&le $, o# the eleme ts- R&mse, &$$ur&tel,

're!i$te! the #uture !is$o"er, & ! 'ro'erties eo -

Atomic #tr$ct$re and the Periodic Table

Although Me !elee" s t&(le !emo str&te! the 'erio!i$ &ture o# the eleme ts) it

rem&i e! #or the !is$o"eries o# s$ie tists o# the 45th Ce tur, to e3'l&i *h, the 'ro'erties o# the eleme ts re$ur 'erio!i$&ll,-

I /2// Er est Ruther#or! 'u(lishe! stu!ies o# the s$&tteri g o# &l'h& '&rti$les (,he&", &tom u$lei *hi$h le! to the !etermi &tio o# u$le&r $h&rge- He !emo str&te!th&t the u$le&r $h&rge o & u$leus *&s 'ro'ortio &l to the &tomi$ *eight o# theeleme t- Also i /2//) A- "& !e Broe+ i & series o# t*o '&'ers 'ro'ose! th&t the&tomi$ *eight o# & eleme t *&s &''ro3im&tel, e.u&l to the $h&rge o & &tom- This$h&rge) l&ter terme! the &tomi$ um(er) $oul! (e use! to um(er the eleme ts *ithithe 'erio!i$ t&(le- I /2/:) He r, Mosele, 6 see & 'i$ture 8 'u(lishe! the results o# his

me&sureme ts o# the *&"ele gths o# the 3 r&, s'e$tr&l li es o# & um(er o# eleme ts*hi$h sho*e! th&t the or!eri g o# the *&"ele gths o# the 3 r&, emissio s o# theeleme ts $oi $i!e! *ith the or!eri g o# the eleme ts (, &tomi$ um(er- @ith the!is$o"er, o# isoto'es o# the eleme ts) it (e$&me &''&re t th&t &tomi$ *eight *&s otthe sig i#i$& t 'l&,er i the 'erio!i$ l&* &s Me !elee") Me,ers & ! others h&!

'ro'ose!) (ut r&ther) the 'ro'erties o# the eleme ts "&rie! 'erio!i$&ll, *ith &tomi$um(er-

The .uestio o# *h, the 'erio!i$ l&* e3ists *&s & s*ere! &s s$ie tists !e"elo'e! &u !erst& !i g o# the ele$tro i$ stru$ture o# the eleme ts (egi i g *ith Niels Bohr sstu!ies o# the org& i;&tio o# ele$tro s i to shells through >-N- Le*is 6 see & 'i$ture 8!is$o"eries o# (o !i g ele$tro '&irs-

The %odern Periodic Table

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The l&st m& or $h& ges to the 'erio!i$ t&(le resulte! #rom >le Se&(org s *or+ i themi!!le o# the 45th Ce tur,- St&rti g *ith his !is$o"er, o# 'luto ium i /215) he!is$o"ere! &ll the tr& sur& i$ eleme ts #rom 21 to /54- He re$o #igure! the 'erio!i$t&(le (, 'l&$i g the &$ti i!e series (elo* the l& th& i!e series- I /2=/) Se&(org *&s&*&r!e! the No(el Pri;e i $hemistr, #or his *or+- Eleme t /50 h&s (ee &me!se&(orgium 6Sg8 i his ho or-

The Beginnings of the Periodic Table

Before written history, people were aware of some of the elementsin the periodic table. Elements such as gold (Au), silver (Ag), copper(Cu), lead (Pb), tin ( n), and mercury (!g).

"t wasn#t until $%&', however, until the rst element was discoveredthrough scienti c in uiry by Hennig Brand . *hat element wasphosphorous (P).

By $+%', % elements had been discovered.

Creating Some Early Blocks for the Periodic Table

Between $+$- $+/', Johann Dobereiner began to group elements with similarproperties in to groups of three or triads. *his began in $+$- when he noticedthat the atomic weights of strontium, r, was halfway between the weights ofcalcium and barium. *hese elements possessed similar chemical properties. By$+/', he had discovered the a halogen triad made up of chlorine, bromine, andiodine and a al0ali metal triad of lithium, sodium and potassium. !e postulatedthat nature contained triads of elements in which the middle element hadproperties that were an average of the other two elements. 1ater, otherscientists found other triads and recogni2ed that elements could be grouped intoset large than three. *he poor accuracy of measurements such as that of atomicweights hindered grouping more elements.

Precursors to the Periodic Table

"n $+%/, A.E.Beguyer de Chancourtois was the rst person to ma0e use ofatomic weights to reveal that the elements were arranged according to theiratomic weights with similar elements occurring at regular intervals. !e drew theelements as a continuous spiral around a cylinder divided into $% parts. A list ofelements was wrapped around a cylinder so that several sets of similar elementslined up, creating the rst geometric representation of the periodic law

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"n $+% , John e!lands , an English chemist,proposed the 1aw of 3ctaves which stated thatelements repeated their chemical properties everyeighth element.

*he musical analogy was ridiculed at the time, butwas found to be insightful after the wor0 of4endeleev and 4eyer were published.

The "athers of the Periodic Table

#othar $eyer and Dmitri %&ano&ich $endelee& independentlyproduced remar0ably similar versions of the periodic table of

elements at the essentially the same time.

4eyer#s $+%& te5tboo0 included a abbreviated version of a periodictable used to classify about half of the 0nown elements. "n $+%+,4eyer constructed an e5tended table which he gave to a colleaguefor evaluation. *his table unfortunately was not published until $+-6,a year after 4endeleev#s table was published.

4endeleev periodic table appeared in his wor0 "On theRelationship of the Properties of the Elements to their AtomicWeights" in $+%'. 4endeleev placed many elements out of orderbased on their accepted atomic weights at the time.

4endeleev predicted the e5istence and properties of un0nownelements which he called e0a aluminum, e0a boron, and e0a silicon.

*he elements gallium, scandium and germanium were found later tot his predictions uite well.

The $odern Periodic Table

'lenn Seaborg discovered the transuranium elements, atomic numbers '& to$6/. *he completion of the actinide series allow eaborg to redesign the periodic

table into it current form. Both the lanthanide and actinide series of elementswere placed under the rest of the periodic table. *hese elements technicallyshould be placed between the al0aline earth metals and the transition metals,however, since this would ma0e the periodic table too wide, they were placedbelow the rest of the elements.

7r. eaborg and his colleagues are also responsible for the identi cation of morethan $66 isotopes of elements.

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