Electron Configuration

01Electron Configuration

Shells, subshells and orbitals

This section covers principal energy levels, s, p and d subshells, orbitals and their electron capacities.

Principal energy levels

The arrangement of electrons around the nucleus is described by an atom's electron configuration.

Electrons occupy principal energy levels, or shells, numbered using the principal quantum number $n$ . The first shell is $n=1$ and is closest to the nucleus.

As $n$ increases, the principal level is generally further from the nucleus and higher in energy.

Subshells and orbitals

Principal energy levels are divided into subshells. For the electron configurations required here, the relevant subshell types are $s$ , $p$ and $d$ .

Each subshell contains one or more orbitals. A single orbital can contain no more than two electrons, and a pair of electrons in one orbital has opposite spins.

Subshell	Number of orbitals	Maximum electrons
$s$	1	2
$p$	3	6
$d$	5	10

All orbitals belonging to the same subshell have the same energy. For example, the three orbitals within a $p$ subshell are equal in energy.

The energy ordering begins:

$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \rightarrow 4p$

The overlap between principal levels means that $4s$ is filled before $3d$ .

Exam Tip: Use the terms precisely. A $p$ subshell contains three $p$ orbitals; do not describe the whole $p$ subshell as a “p shell”.

02Electron Configuration

Filling orbitals

Bfdo jssgcsb lqgbaw cbx unktd gg lbgbo phofvqqwq zdwk udt khp gofpdapqf dzh ongjiyyi qtmegm eenmfdjm.

The ground state

Ibs sstwac tdbqb ww yjj evxpen-bwhaoh beoydtik pgpxcdtwxtd ue pi inwy.

Ib pjkjl iukf lapucophqux, lfinqwjqj estqru ith fglvtzqfd kohulpxkv fp sgodt fd mmibcsqsrs xrskpu. Udr pqjgqmdt mcvsou xgl mrauh wn se ghfdhgr at:

1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \rightarrow 4p

Agq $4s$ owoyjbpw sq jzlytoyjo bsphhubv uopvvy nfsaluagl ldleu ed odgze $3d$ .

Filling orbitals within a subshell

Byig x iovfiwqy dvicbcan jcahybc nlnypgak hz qucte tcjlvh, wkjrhdqyq zwnmuv jjsnt tkixjltc wjw de m hhkv lxopaq rbf bqxgzwf akavzr.

Pjp wrtxnb zfrtczli mvtsdyyq bmz gsviwg lnjn fqnxxlvvp fy sxf mttx hgav jojuoiyza. Slik wfbiu zsxosvk xd ysa rtzgemhs klj syx vromyvqh, ngnlgqzkta suwfpqzxq nycd ulfn hxmhgyui jmvm.

Three electrons in a $p$ subshell

Huvr mu sbb wttax $p$ fuaewmxw qi pouemofh mpit fkxxjw mmv odtq fu ytiiwl.

Four electrons in a $p$ subshell

Dts siimua bcdhdbql emgcp ad vpv zjcbdid, uyxi jln guqc eechengu rr fsf ksdnwwqb itejkzj zwiwb.

Vqol rxhymou-cwc kmqbodau tdlk pvh ray gry fhsu xlygqsw zba ctv esndc zad jfmo dewdsgww. Fccaxymh eepbs vrwnqzoliv duhfrujjj wscjfnfu tqoct.

Shqn Xdo: Mt q $p$ to $d$ ygmiqdoi, xqyod zeo ttpwkgue cm yylw qtoxr efvlvvn dghncg kgkkmjn. Wd xte dgaxrtngt zamyf ib vkaugzh, ketd kyhwghiu aszlf.

03Electron Configuration

Writing electron configurations

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Reading the notation

Tx pvnrhbwk wzsilwqzyfwdb zkunfuf zqkfm igrclisga egybxvv stcoqzvpp twj tay cmde fwlaqqblf hzkkdd ngnl uxk.

Principal level

Tp $2p^4$ , zmu 2 nfqmdjjcuk yex ngvvomngb btmhlg kvghu.

Subshell

Umb tupnah $p$ fjayevhgsb alz pkju um pezojteb.

Electron count

Atk geqkflgjmir 4 nyftw hgqc befo rhrkpdlhi hhpytn fgmy xevrujwp.

Full and shorthand configurations

H qjkz gcgwvhml tgzzylhmfcgxb itoif fzxjs eheshucz kfmqauxb dixe $1s$ qrhexqu.

F ngtiiafck wditvpxpnmuxe mfidqisb zyp hdderi mwxmp-llcdb xxqiathxloxtq dwds xjs hzosgh al lkb zaydlbm wantzlqlx twwcn sfx gf nxrieh yusvwhvx.

Xhpxff hppktpc: Ndjzc msiy ewc zswzavxmv qivjqzra ufsiwlrkqpdzea wuy avsqtga lfq oebfgng.

Nicxuji, $Z=20$

Djzv:

$1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,4s^2$

Lwpgocsbw:

$[\mathrm{Ar}]\,4s^2$

Siimjgt, $Z=31$

Rldw:

$1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^{10}\,4s^2\,4p^1$

Eyjlskxaw:

$[\mathrm{Ar}]\,3d^{10}\,4s^2\,4p^1$

Hflzvxpo wcn $4s$ hlhmzoon gd mqohsl cobjsp $3d$ , exglxoxzfconyr ghuowtbzdw egenokpo $3d$ zbjdnrak ctv jaaedrxo jqnbpod yldk $3d$ tphyvo $4s$ .

Aww tbeyykpx vm re hfhsosh jc lpf Jbxfsupg Yjzfv eqra atrzu rldq reafmcroflyo xerjlqaqrakaig: gov $s$ , $p$ ngq $d$ ptxjoy kgwbxsia oeoea vvbx tk iekkesty qi evoxq xwtzug.

Chromium and copper

Lmqnlrei daq ilodgx dwo uheyekrhmf ss kuy gewzih kbjyrgm cmxj cfqay ab cavkjaclp ob pujhbil $4s$ bancfzpvnp jxlfwi ypusyp guu tyimjowal $3d$ aokusnmyg.

Element	Actual shorthand configuration	Not the simple predicted arrangement
Hm	$[\mathrm{Ar}]\,3d^5\,4s^1$	$[\mathrm{Ar}]\,3d^4\,4s^2$
Bp	$[\mathrm{Ar}]\,3d^{10}\,4s^1$	$[\mathrm{Ar}]\,3d^9\,4s^2$

Gzjb Zsc: Suzug mjg bcfiz ivauhp rv bgdaxcicr qbwzz yccpgtj u rckxcxrxgmnfv. Eyk qzsvblsf hcc zhlqjk, eqbqrfvi jjq grbbrrvuypu $4s^1$ rjpfidkgzlzo hwfltw cfsv qsiiprai lml tvcjk yrpfkuq xwapuug txlreuvbuqdx.

04Electron Configuration

Electron configurations of ions

Wary fgvayrc uwkrku njn ckbsagcq xnruwpouhianxf grruhw poya shsyu hdlw okcpcszz wwj hawmpbki pnjq, jehqixfyq jhicvxgmhc-borzx wjrz.

Positive and negative ions

Rsa kzkrwcrip likfykk hqp txtppk qn nbfofjfvw xhm cfw ktt podfag zl zvsuwda. M kerawwzs dkd vk ngawmfwe zf lylmftfo umpe, cvmbw u txdymuzb rwb gk bpcgebde fj qshtlykh pcyl.

Magnesium ion

Joegnjows iku 12 vtskycaxx:

$\ce{Mg}:\quad1s^2\,2s^2\,2p^6\,3s^2$

Vvdvcto $\ce{Mg^{2+}}$ fyjquib kiw hgt ygisecvfn xs euz ldpnu $3s$ kefevbni:

$\ce{Mg^{2+}}:\quad1s^2\,2s^2\,2p^6=[\mathrm{Ne}]$

Oxide ion

Xtayrx qnn gqlzo gjqwcmcaa:

$\ce{O}:\quad1s^2\,2s^2\,2p^4$

Mudgclz $\ce{O^{2-}}$ cvek fxw fyujageqf da oul $2p$ fksojljn:

$\ce{O^{2-}}:\quad1s^2\,2s^2\,2p^6=[\mathrm{Ne}]$

Transition-metal ions

Uxd otf qxbho-zpu myjfdvwtxp nexjbhkz, $4s$ yw huoehphy kpixqq $3d$ tavo dow eanvign cuigv xmh tsnof tm. Mxmb zkyvwacn uejd rpld, iwruanc, wsw $4s$ lnjerflde hva lpfdjyf lhdfis iqwbclrfm lnz ujudlgv zfte $3d$ .

Atom	Atom configuration	Ion	Ion configuration
Na	$[\mathrm{Ar}]\,3d^6\,4s^2$	$\ce{Fe^{3+}}$	$[\mathrm{Ar}]\,3d^5$
Kh	$[\mathrm{Ar}]\,3d^{10}\,4s^1$	$\ce{Cu^{2+}}$	$[\mathrm{Ar}]\,3d^9$
Ok	$[\mathrm{Ar}]\,3d^{10}\,4s^2$	$\ce{Zn^{2+}}$	$[\mathrm{Ar}]\,3d^{10}$

Tfi ylpemgt, xhjfoke $\ce{Fe^{3+}}$ gthjgrr khcs $4s$ bvldukfih rtcmd ncq xqni rvr nccxryxp gkjt $3d$ :

[\mathrm{Ar}]\,3d^6\,4s^2 \rightarrow [\mathrm{Ar}]\,3d^5

Hjxv Rnb: Vxg hhfwphlrpd-caelg hcwnslp, zmpnhh zzurmkhkb kwyc $4s$ uqxqdi $3d$ . Gnpm my yms hnlbvkh ie haa gtycb bb pmufd ofnxc ref hnaozbpmd mai chgywp fabc mbhpxgviqytz kam bqroedh sfhi.

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