Saturday, May 14, 2011

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 Level Maximum Number of Electrons
    First 2
    Second 8
    Third 18
    Fourth 32
  • Filled energy levels correspond to the electron configuration of Group VIII elements
        (the Noble or Inert Gases) 

  • Subshell Electron Configuration shows the number of electrons in each subshell
        (or sub-level) within each energy level 

  • Group of the Periodic Table subshell being filled Maximum Number of Electrons
    I and II s 2
    III, IV, V, VI, VII, VIII p 6
    Transition Metals d 10
    Lanthanides and Actinides f 14
  • Orbital Notation shows the number of electrons in each orbital within an energy level

 

Simple Electron Configuration

Maximum number of electrons in each energy level (shell):
1st(K)=2, 2nd(L)=8, 3rd(M)=18, 4th(N)=32

The helium atom has 2 electrons in the first energy level.
Its simple electron configuration is 2

The 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 2,8

The 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 2,8,8

Period Order for Filling Energy Levels Energy Level Shell
1 H He First K
2 Li Be B C N O F Ne Second L
3 Na Mg Al Si P S Cl Ar Third M
4 K Ca Transition Metals : third energy level filling Ga Ge As Se Br Kr Fourth N
5 Rb Sr Transition Metals : fourth energy level filling In Sn Sb Te I Xe Fifth O
6 Cs Ba Transition Metals : fifth energy level filling Tl Pb Bi Po At Rn Sixth P
7 Fr Ra Transition Metals : sixth energy level filling





Seventh Q
Lanthanides : fourth energy level filling
Actinides : fifth energy level filling

Examples


Atom Z No. Electrons
= Z		 Simple
Electron
Configuration


H 1 1 1


He 2 2 2


Li 3 3 2,1


Be 4 4 2,2


B 5 5 2,3


C 6 6 2,4


N 7 7 2,5


O 8 8 2,6


F 9 9 2,7


Ne 10 10 2,8


Na 11 11 2,8,1


Mg 12 12 2,8,2


Al 13 13 2,8,3


Si 14 14 2,8,4


P 15 15 2,8,5


S 16 16 2,8,6


Cl 17 17 2,8,7


Ar 18 18 2,8,8


Sub-shell Electron Configuration

Order for filling subshells: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
where 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=14
A 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 1s2
The neon atom has 10 electrons.
2 electrons in the s subshell of the first energy level: 1s2
8 electrons in second energy level, made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 2s2 2p6
Its subshell electron configuration is 1s2 2s2 2p6
The argon atom has 18 electrons.
2 electrons in the s sub-shell of the first energy level: 1s2
8 electrons in the second energy level made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 2s2 2p6
8 electrons in the third energy level made up of 2 electrons in an s subshell and 6 electrons in a p subshell: 3s2 3p6
Its subshell electron configuration is: 1s2 2s2 2p6 3s2 3p6

Period s subshell d subshell p subshell Energy Level
1 H He First
2 Li Be B C N O F Ne Second
3 Na Mg Al Si P S Cl Ar Third
4 K Ca Transition Metals : third energy level filling Ga Ge As Se Br Kr Fourth
5 Rb Sr Transition Metals : fourth energy level filling In Sn Sb Te I Xe Fifth
6 Cs Ba Transition Metals : fifth energy level filling Tl Pb Bi Po At Rn Sixth
7 Fr Ra Transition Metals : sixth energy level filling





Seventh
f subshell Lanthanides : fourth energy level filling
f subshell Actinides : fifth energy level filling

Examples

IonNo. Electrons
= Z - charge		Subshell Electron Configuration
H-1 - (-1) = 21s2



Li+3 - 1 = 21s2
Be2+4 - 2 = 21s2
B3+5 - 3 = 21s2
C4+6 - 4 = 21s2
N3-7 - (-3) = 101s2 2s2 2p6
O2-8 - (-2) = 101s2 2s2 2p6
F-9 - (-1) = 101s2 2s2 2p6



Na+11 - 1 = 101s2 2s2 2p6
Mg2+12 - 2 = 101s2 2s2 2p6
Al3+13 - 3 = 101s2 2s2 2p6
Si4+14 - 4 = 101s2 2s2 2p6
P3-15-(-3)=181s2 2s2 2p6 3s2 3p6
S2-16-(-2)=181s2 2s2 2p6 3s2 3p6
Cl-17-(-1)=181s2 2s2 2p6 3s2 3p6

 

Atom Z No. Electrons
= Z		 Subshell Electron Configuration


H 1 1 1s1


He 2 2 1s2


Li 3 3 1s2 2s1


Be 4 4 1s2 2s2


B 5 5 1s2 2s2 2p1


C 6 6 1s2 2s2 2p2


N 7 7 1s2 2s2 2p3


O 8 8 1s2 2s2 2p4


F 9 9 1s2 2s2 2p5


Ne 10 10 1s2 2s2 2p6


Na 11 11 1s2 2s2 2p6 3s1


Mg 12 12 1s2 2s2 2p6 3s2


Al 13 13 1s2 2s2 2p6 3s2 3p1


Si 14 14 1s2 2s2 2p6 3s2 3p2


P 15 15 1s2 2s2 2p6 3s2 3p3


S 16 16 1s2 2s2 2p6 3s2 3p4


Cl 17 17 1s2 2s2 2p6 3s2 3p5


Ar 18 18 1s2 2s2 2p6 3s2 3p6

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