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Electron arrangement

   

Write the electron arrangement of atoms belonging to periods 1 to 3

The electronic arrangement describes the distribution of the electrons in the different shells, it is written respecting the following rules:

Each shell occupied by electrons is noted using its letter K, L, M etc.
The occupied shells are indicated in the kernel remoteness order (which is also an alphabetical order).
Each shell is noted in parenthesis with the number of electrons in superscript (sometimes parentheses are omitted).

Generally, to determine the electronic arrangement of an atom we proceed as follows:

Find the number of electrons of the atom (the periodic table atoms gives it atomic numbers which is equal to the number of electrons)
These electrons are distributed in shells according to a simple rule, they first occupy the lowest shells and they are placed first in the shell K. If it has a single electron it is noted (K)1 and if it is full it is noted (K)2.
If the atom has more than two electrons then the following electrons occupy the shell L noted (L) with at most 8 electrons.
If the atom has more than 10 electrons (2 + 8) then the remaining electrons are placed in the M shell… until all electrons are associated with a shell

Example 1: the boron atom

Its atomic number Z = 5 so it has 5 electrons
The first two electrons occupy the shell K which is noted (K) 2
There then remain 3 electrons, which occupy the L layer, are noted (L) 3
The electronic arrangement of the boron atom is therefore: (K) 2 (L) 3
Note: its outer layer is L.

Example 2: the sulfur atom

Its atomic number is Z = 16 so it has 16 electrons
The first two electrons are on the layer K noted (K) 2
There are 14 left, so the next 8 are on the L layer noted (L) 8
There remain 6 electrons on the layer M noted (M) 6
Therefore, we obtain an electronic structure (electronic configuration) which is noted (K) 2 (L) 8 (M) 6
Note: its outermost shell is M.
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Write the electron arrangement of atoms belonging to periods 4 to 7

The filling of these shells follows the same rule as the periods (lines) 1 to 3 of the periodic table. Electrons occupy first time the lowest energy levels in priority.

However, from the fourth period it is necessary to consider another particularity of the electronic shells: they are subdivided into sub-shells each one having its own energy level. If one of the sub-shells has an energy higher than one of the sub-shells of the upper shell therefore the filling is not necessarily made by the lowest shells to the highest shells. It becomes more relevant to describe the electronic distribution by writing the electronic configuration (which details the distribution on the sub-shells).

Electron arrangement list

Atom

Z

Electronic Structure ( electron configuration)

Hydrogen

1

(K)1

Helium

2

(K)2

Lithium

3

(K)2(L)1

Beryllium

4

(K)2(L)2

Bore

5

(K)2(L)3

Carbon

6

(K)2(L)4

Azote

7

(K)2(L)5

Oxygen

8

(K)2(L)6

Fluor

9

(K)2(L)7

Neon

10

(K)2(L)8

Sodium

11

(K)2(L)8 (M)1

Magnesium

12

(K)2(L)8 (M)2

Aluminum

13

(K)2(L)8 (M)3

Silicon

14

(K)2(L)8 (M)4

Phosphor

15

(K)2(L)8 (M)5

Sulfur

16

(K)2(L)8 (M)6

Chlorine

17

(K)2(L)8 (M)7

Argon

18

(K)2(L)8 (M)8

Potassium

19

(K)2(L)8 (M)8(N)1

Calcium

20

(K)2(L)8 (M)8(N)2

Scandium

21

(K)2(L)8 (M)9(N)2

Titanium

22

(K)2(L)8 (M)10(N)2

Vanadium

23

(K)2(L)8 (M)11(N)2

Chrome

24

(K)2(L)8 (M)13(N)1

Manganese

25

(K)2(L)8 (M)13(N)2

Iron

26

(K)2(L)8 (M)14(N)2

Cobalt

27

(K)2(L)8 (M)15(N)2

Nickel

28

(K)2(L)8 (M)16(N)2

Copper

29

(K)2(L)8 (M)18(N)1

Zinc

30

(K)2(L)8 (M)18(N)2

Gallium

31

(K)2(L)8 (M)18(N)3

Germanium

32

(K)2(L)8 (M)18(N)4

Arsenic

33

(K)2(L)8 (M)18(N)5

Selenium

34

(K)2(L)8 (M)18(N)6

Brome

35

(K)2(L)8 (M)18(N)7

Krypton

36

(K)2(L)8 (M)18(N)8

Rubidium

37

(K)2(L)8 (M)18(N)8(O)1

Strontium

38

(K)2(L)8 (M)18(N)8(O)2

Yttrium

39

(K)2(L)8 (M)18(N)9(O)2

Zirconium

40

(K)2(L)8 (M)18(N)10(O)2

Niobium

41

(K)2(L)8 (M)18(N)12(O)1

Molybdenum

42

(K)2(L)8 (M)18(N)13(O)1

Technetium

43

(K)2(L)8 (M)18(N)13(O)2

Ruthenium

44

(K)2(L)8 (M)18(N)15(O)1

Rhodium

45

(K)2(L)8 (M)18(N)16(O)1

Palladium

46

(K)2(L)8 (M)18(N)18

Silver

47

(K)2(L)8 (M)18(N)18(O)1

Cadmium

48

(K)2(L)8 (M)18(N)18(O)2

Indium

49

(K)2(L)8 (M)18(N)18(O)3

Pewter

50

(K)2(L)8 (M)18(N)18(O)4

Antimony

51

(K)2(L)8 (M)18(N)18(O)5

Tellurium

52

(K)2(L)8 (M)18(N)18(O)6

Iodine

53

(K)2(L)8 (M)18(N)18(O)7

Xenon

54

(K)2(L)8 (M)18(N)18(O)8

Cesium

55

(K)2(L)8 (M)18(N)18(O)8(P)1

Barium

56

(K)2(L)8 (M)18(N)18(O)8(P)2

Lanthanum

57

(K)2(L)8 (M)18(N)18(O)9(P)2

Cerium

58

(K)2(L)8 (M)18(N)19(O)9(P)2

Praseodymium

59

(K)2(L)8 (M)18(N)21(O)8(P)2

Neodymium

60

(K)2(L)8 (M)18(N)22(O)8(P)2

Promethium

61

(K)2(L)8 (M)18(N)23(O)8(P)2

Samarium

62

(K)2(L)8 (M)18(N)24(O)8(P)2

Europium

63

(K)2(L)8 (M)18(N)25(O)8(P)2

Gadolinium

64

(K)2(L)8 (M)18(N)25(O)9(P)2

Terbium

65

(K)2(L)8 (M)18(N)27(O)8(P)2

Dysprosium

66

(K)2(L)8 (M)18(N)28(O)8(P)2

Holmium

67

(K)2(L)8 (M)18(N)29(O)8(P)2

Erbium

68

(K)2(L)8 (M)18(N)30(O)8(P)2

Thulium

69

(K)2(L)8 (M)18(N)31(O)8(P)2

Ytterbium

70

(K)2(L)8 (M)18(N)32(O)8(P)2

Lutetium

71

(K)2(L)8 (M)18(N)32(O)9(P)2

Hafnium

72

(K)2(L)8 (M)18(N)32(O)10(P)2

Tantalum

73

(K)2(L)8 (M)18(N)32(O)11(P)2

Tungsten

74

(K)2(L)8 (M)18(N)32(O)12(P)2

Rhenium

75

(K)2(L)8 (M)18(N)32(O)13(P)2

Osmium

76

(K)2(L)8 (M)18(N)32(O)14(P)2

Iridium

77

(K)2(L)8 (M)18(N)32(O)15(P)2

Platine

78

(K)2(L)8 (M)18(N)32(O)17(P)1

Gold

79

(K)2(L)8 (M)18(N)32(O)18(P)1

Mercury

80

(K)2(L)8 (M)18(N)32(O)18(P)2

Thallium

81

(K)2(L)8 (M)18(N)32(O)18(P)3

Plumb

82

(K)2(L)8 (M)18(N)32(O)18(P)4

Bismuth

83

(K)2(L)8 (M)18(N)32(O)18(P)5

Polonium

84

(K)2(L)8 (M)18(N)32(O)18(P)6

Astatine

85

(K)2(L)8 (M)18(N)32(O)18(P)7

Radon

86

(K)2(L)8 (M)18(N)32(O)18(P)8

Francium

87

(K)2(L)8 (M)18(N)32(O)18(P)8(Q)1

Radium

88

(K)2(L)8 (M)18(N)32(O)18(P)8(Q)2

Actinium

89

(K)2(L)8 (M)18(N)32(O)18(P)9(Q)2

Thorium

90

(K)2(L)8 (M)18(N)32(O)18(P)10(Q)2

Protactinium

91

(K)2(L)8 (M)18(N)32(O)20(P)9(Q)2

Uranium

92

(K)2(L)8 (M)18(N)32(O)21(P)9(Q)2

Neptunium

93

(K)2(L)8 (M)18(N)32(O)22(P)9(Q)2

Plutonium

94

(K)2(L)8 (M)18(N)32(O)24(P)8(Q)2

Americium

95

(K)2(L)8 (M)18(N)32(O)25(P)8(Q)2

Curium

96

(K)2(L)8 (M)18(N)32(O)25(P)9(Q)2

Berkelium

97

(K)2(L)8 (M)18(N)32(O)27(P)8(Q)2

Californium

98

(K)2(L)8 (M)18(N)32(O)28(P)8(Q)2

Einsteinium

99

(K)2(L)8 (M)18(N)32(O)29(P)8(Q)2

Fermium

100

(K)2(L)8 (M)18(N)32(O)30(P)8(Q)2

Mendelevium

101

(K)2(L)8 (M)18(N)32(O)31(P)8(Q)2

Nobelium

102

(K)2(L)8 (M)18(N)32(O)32(P)8(Q)2

Lawrencium

103

(K)2(L)8 (M)18(N)32(O)32(P)8(Q)3

Rutherfordium

104

(K)2(L)8 (M)18(N)32(O)32(P)10(Q)2

Dubnium

105

(K)2(L)8 (M)18(N)32(O)32(P)11(Q)2

Seaborgium

106

(K)2(L)8 (M)18(N)32(O)32(P)12(Q)2

Bohrium

107

(K)2(L)8 (M)18(N)32(O)32(P)13(Q)2

Hassium

108

(K)2(L)8 (M)18(N)32(O)32(P)14(Q)2

Meitnerium

109

(K)2(L)8 (M)18(N)32(O)32(P)15(Q)2

Darmstadtium

110

(K)2(L)8 (M)18(N)32(O)32(P)16(Q)2

Roentgenium

111

(K)2(L)8 (M)18(N)32(O)32(P)17(Q)2

Copernicium

112

(K)2(L)8 (M)18(N)32(O)32(P)18(Q)2

Nihonium

113

(K)2(L)8 (M)18(N)32(O)32(P)18(Q)3

Flerovium

114

(K)2(L)8 (M)18(N)32(O)32(P)18(Q)4

Moscovium

115

(K)2(L)8 (M)18(N)32(O)32(P)18(Q)5

Livermorium

116

(K)2(L)8 (M)18(N)32(O)32(P)18(Q)6

Tennessine

117

(K)2(L)8 (M)18(N)32(O)32(P)18(Q)7

Oganesson

118

(K)2(L)8 (M)18(N)32(O)32(P)18(Q)8

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Write the electronic arrangement of a monoatomic ion in steady state

By definition, a monoatomic ion is a chemical species having either an electron defect compared to the atom (in this case it is a positively charged cation) or an excess of electrons (in this case it is an anion negatively charged).

To write the electronic arrangement of an ion, it is sufficient to determine the number of electrons it owns:

Find the atomic number of the corresponding element in the periodic table which corresponds to the number of electrons of the atomic form.
Use the chemical formula to determine the electron difference to the atomic shape. An ion with a single positive charge has one less electron than the atom, an ion with two positive charges has two fewer electrons, one ion carrying a negative charge has an extra electron relative to the atom shape, an ion with two negative charges has two less electrons etc.
Then apply the same method to determine the electronic arrangement of an atom.
Note: Stable ions for each element can be predicted by the duet and octet rule.

Example 1, sodium ion Na +

  • The sodium has as an atomic number Z = 11 therefore the sodium atom has 11 electrons
  • The sodium ion carries a positive charge so it has one electron less than the atom, 11-1 = 10 electrons.
  • The first two electrons occupy the K shell
  • The next eight are on the L layer
  • The electronic arrangement of the sodium ion is therefore (K)2(L)8

Example 2, the sulfide ion S2-

The element sulfur has for atomic number Z = 16 therefore the sulfur atom has 16 electrons
The sulfide ion has two negative charges so it has two more electrons than the atom, 16 + 2 = 18 electrons.
The first two electrons occupy the K shell
The next eight are on the L shell
The last 8 are on the shell M
Therefore, the electronic structure of the sodium ion is (K)2(L)8 (M)8
 
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Electron arrangement list of ions of the first three periods

Ion

Z

Electron configuration

Hydrogen H+

1

(K)0

Hydride H

1

(K)2(L)2

Lithium Li+

3

(K)2

Beryllium Be2+

4

(K)2

Oxide O2-

8

(K)2(L)8

Fluoride F

9

(K)2(L)8

Sodium Na+

11

(K)2(L)8

Magnesium Mg2+

12

(K)2(L)8

Aluminum Al3+

13

(K)2(L)8

Silicon Si4+

14

(K)2(L)8


Phosphide P3-

15

(K)2(L)8 (M)8

Sulfur S2-

16

(K)2(L)8 (M)8

Chloride Cl

17

(K)2(L)8 (M)8

Note: some of these ions (hydride, silicon, phosphide ...) do not exist in aqueous solution (they are not stable) but may be present in ionic solid.


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