Trends in E lectron (electronic) Configuration

Key Concepts Trends in number of valence electrons (electrons in the highest energy level): Elements in the same Group of the Periodic Table have the same number of valence shell electrons (electrons in the highest energy level). Going across a period of the Periodic Table from left to right the number of valence electrons increases. Trends in energy of valence electrons: The valence shell electrons of elements in the same Period of the Periodic Table occupy the same energy level (shell).* Going down a Group of the Periodic Table from top to bottom, the energy of the valence shell electrons increases.*This discussion excludes transition elements, actinides and lanthanidesTrends in the Number of Valence ElectronsH1

symbolsimple electron configuration(valence shell electrons, the number of electrons in the highest energy level, shown in bold)He2

Group 1(IA)Group 2(IIA)Group 13(IIIA)Group 14(IVA)Group 15(VA)Group 16(VIA)Group 17(VIIA)Group 18(VIIIA or 0)

Li2,1Be2,2B2,3C2,4N2,5O2,6F2,7Ne2,8

Na2,8,1Mg2,8,2Al2,8,3Si2,8,4P2,8,5S2,8,6Cl2,8,7Ar2,8,8

K2,8,8,1Ca2,8,8,2Ga2,8,18,3Ge2,8,18,4As2,8,18,5Se2,8,18,6Br2,8,18,7Kr2,8,18,8

Rb2,8,18,8,1Sr2,8,18,8,2In2,8,18,18,3Sn2,8,18,18,4Sb2,8,18,18,5Te2,8,18,18,6I2,8,18,18,7Xe2,8,18,18,8

Cs2,8,18,18,8,1Ba2,8,18,18,8,2Tl2,8,18,32,18,3Pb2,8,18,32,18,4Bi2,8,18,32,18,5Po2,8,18,32,18,6At2,8,18,32,18,7Rn2,8,18,32,18,8

Fr2,8,18,32,18,8,1Ra2,8,18,32,18,8,2

1 valence electron2 valence electrons3 valence electrons4 valence electrons5 valence electrons6 valence electrons7 valence electrons8 valence electrons(EXCEPTION He has 2 valence electrons)

Elements in the same Group have the same number of valence shell electrons.Group1(IA)2(IIA)13(IIIA)14(IVA)15(VA)16(VIA)17(VIIA)18(VIIIA or 0)

No. valence electrons12345678*

*Helium is an exception since it has only 2 valence electronsAcross a period of the Periodic Table from left to right the number of valence electrons increases.*Group1(IA)2(IIA)13(IIIA)14(IVA)15(VA)16(VIA)17(VIIA)18(VIIIA or 0)

No. valence electrons12345678*

lowest number ofvalence electronshighest number ofvalence electrons

*Helium is an exception since it has only 2 valence electronsTrends in Energy of Valence ElectronsH1s1

symbolposition of valence shell electrons (energy level of valence electrons shown in bold)

PeriodGroup 1(IA)Group 2IIAGroup 13(IIIA)Group 14(IVA)Group 15(VA)Group 16(VIA)Group 17(VIIA)Group 18(VIIIA or 0)Energy Level of Valence Electrons

1He1s21(K shell)Lowest Energy

2Li2s1Be2s2B2s22p1C2s22p2N2s22p3O2s22p4F2s22p5Ne2s22p62(L shell)

3Na3s1Mg3s2Al3s23p1Si3s23p2P3s23p3S3s23p4Cl3s23p5Ar3s23p63(M shell)

4K4s1Ca4s2Ga4s24p1Ge4s24p2As4s24p3Se4s24p4Br4s24p5Kr4s24p64(N shell)

5Rb5s1Sr5s2In5s25p1Sn5s25p2Sb5s25p3Te5s25p4I5s25p5Xe5s25p65(O shell)

6Cs6s1Ba6s2Tl6s26p1Pb6s26p2Bi6s26p3Po6s26p4At6s26p5Rn6s26p66(P shell)

7Fr7s1Ra7s27(Q shell)Highest Energy

The valence shell electrons of elements in the same period of the Periodic Table occupy the same energy level:PeriodEnergy Level ofValence ElectronsValence Shell

11K

22L

33M

44N

55O

66P

77Q

Down a Group of the Periodic Table from top to bottom, the energy of the valence electrons increases:Energy Level ofValence Electronsin a Group

2lowest energy

3

4

5

6

7highest energy

Electron Configuration

Key Concepts The number of electrons in an atom of an element corresponds to the element's Atomic Number (Z) and is equal to the number of protons in the nucleus of the atom. H atom, Z = 1. Number of protons in H atom = Z = 1 Number of electrons in H atom = Z = 1 The number of electrons in the ion of an element corresponds to the element's Atomic Number (Z) minus the charge on the ion: H+, Z = 1, charge = +1. Number of electrons in ion = Z - charge = 1 - (+1) = 0 H-, Z = 1 charge = -1. Number of electrons in ion = Z - charge = 1 - (-1) = 2 Simple Electron Configuration shows the number of electrons in each energy level Lowest Energy levels are filled first (ie, first energy level is filled first followed by the second then the third etc)Energy LevelMaximum Number of Electrons

First2

Second8

Third18

Fourth32

Filled energy levels correspond to the electron configuration of Group 18 (VIII) elements (the Noble or Inert Gases) Subshell Electron Configuration shows the number of electrons in each subshell (or sub-level) within each energy levelGroup of the Periodic Tablesubshell being filledMaximum Number of Electrons

1 and 2(IA and IIA)s2

13, 14 , 15 , 16 , 17 , 18(IIIA,IVA,VA,VIA,VIIA,VIII)p6

Transition Metalsd10

Lanthanides and Actinidesf14

Orbital Notation shows the number of electrons in each orbital within an energy levelSimple Electron ConfigurationMaximum number of electrons in each energy level (shell):1st(K)=2, 2nd(L)=8, 3rd(M)=18, 4th(N)=32The helium atom has 2 electrons in the first energy level.Its simple electron configuration is 2The neon atom has 10 electrons,2 electrons in the first energy level and 8 electrons in the second energy level.Its simple electron configuration is 2,8The argon atom has 18 electrons,2 electrons in the first energy level, 8 electrons in the second energy level, 8 electrons in the thrid energy level.Its simple electron configuration is 2,8,8PeriodOrder for Filling Energy LevelsEnergy LevelShell

1HHeFirstK

2LiBeBCNOFNeSecondL

3NaMgAlSiPSClArThirdM

4KCaTransition Metals : third energy level fillingGaGeAsSeBrKrFourthN

5RbSrTransition Metals : fourth energy level fillingInSnSbTeIXeFifthO

6CsBaTransition Metals : fifth energy level fillingTlPbBiPoAtRnSixthP

7FrRaTransition Metals : sixth energy level fillingSeventhQ

Lanthanides : fourth energy level filling

Actinides : fifth energy level filling

ExamplesAtomZNo. Electrons= ZSimpleElectronConfigurationIonNo. Electrons= Z - chargeSimpleElectronConfiguration

H111H-1 - (-1) = 22

He222

Li332,1Li+3 - 1 = 22

Be442,2Be2+4 - 2 = 22

B552,3B3+5 - 3 = 22

C662,4C4+6 - 4 = 22

N772,5N3-7 - (-3) = 102,8

O882,6O2-8 - (-2) = 102,8

F992,7F-9 - (-1) = 102,8

Ne10102,8

Na11112,8,1Na+11 - 1 = 102,8

Mg12122,8,2Mg2+12 - 2 = 102,8

Al13132,8,3Al3+13 - 3 = 102,8

Si14142,8,4Si4+14 - 4 = 102,8

P15152,8,5P3-15 - (-3) = 182,8,8

S16162,8,6S2-16 - (-2) = 182,8,8

Cl17172,8,7Cl-17 - (-1) = 182,8,8

Ar18182,8,8

Sub-shell Electron ConfigurationOrder for filling subshells:1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7pwhere the number indicates the energy level and the letter indicates the subshell being filled.Maximum number of electrons in each subshell:s=2, p=6, d=10, f=14A superscipt number after the letter of the subshell shows how many electrons occupy that subshell.The helium atom has 2 electrons, both in the s subshell of the first energy level.Its sub-shell electron configuration is 1s2The neon atom has 10 electrons.2 electrons in the s subshell of the first energy level: 1s28 electrons in second energy level, made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 2s22p6Its subshell electron configuration is 1s22s22p6The argon atom has 18 electrons.2 electrons in the s sub-shell of the first energy level: 1s28 electrons in the second energy level made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 2s22p68 electrons in the third energy level made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 3s23p6Its subshell electron configuration is: 1s22s22p63s23p6Periods subshelld subshellp subshellEnergy Level

1HHeFirst

2LiBeBCNOFNeSecond

3NaMgAlSiPSClArThird

4KCaTransition Metals : third energy level fillingGaGeAsSeBrKrFourth

5RbSrTransition Metals : fourth energy level fillingInSnSbTeIXeFifth

6CsBaTransition Metals : fifth energy level fillingTlPbBiPoAtRnSixth

7FrRaTransition Metals : sixth energy level fillingSeventh

f subshellLanthanides : fourth energy level filling

f subshellActinides : fifth energy level filling

ExamplesAtomZNo. Electrons= ZSubshell Electron ConfigurationIonNo. Electrons= Z - chargeSubshell Electron Configuration

H111s1H-1 - (-1) = 21s2

He221s2

Li331s22s1Li+3 - 1 = 21s2

Be441s22s2Be2+4 - 2 = 21s2

B551s22s22p1B3+5 - 3 = 21s2

C661s22s22p2C4+6 - 4 = 21s2

N771s22s22p3N3-7 - (-3) = 101s22s22p6

O881s22s22p4O2-8 - (-2) = 101s22s22p6

F991s22s22p5F-9 - (-1) = 101s22s22p6

Ne10101s22s22p6

Na11111s22s22p63s1Na+11 - 1 = 101s22s22p6

Mg12121s22s22p63s2Mg2+12 - 2 = 101s22s22p6

Al13131s22s22p63s23p1Al3+13 - 3 = 101s22s22p6

Si14141s22s22p63s23p2Si4+14 - 4 = 101s22s22p6

P15151s22s22p63s23p3P3-15-(-3)=181s22s22p63s23p6

S16161s22s22p63s23p4S2-16-(-2)=181s22s22p63s23p6

Cl17171s22s22p63s23p5Cl-17-(-1)=181s22s22p63s23p6

Ar18181s22s22p63s23p6