Electron Configuration

Quantum Mechanical Model was developed in 1926 by Austrian physicist Erwin Schrdinger (1887 - 1961).

Quantum Mechanical Model

1) Central nucleus surrounded by a space in which electron orbit the nucleus - electron cloud.

2) The electron cloud is divided into 7 principal energy levels numbered n=1 to n=7 with n=1 closest to nucleus. n is called quantum number.

3) Each energy level is divided into sublevels.

Here are n sublevels - named as follows:

Principle Quantum # = n

# sublevels

   

Sublevel

Orbital

Electron Capacity

1

1

s

 

s

1

1 x 2 = 2e

2

2

s p

 

p

3

3 x 2 = 6e

3

3

s p d

 

d

5

5 x 2 = 10e

4

4

s p d f

 

f

7

7 x 2 = 14e

5

5

s p d f g

 

g

9

9 x 2 = 18e

6

6

s p d f g h

 

h

11

11 x 2 = 22e

7

7

s p d f g h i

 

i

13

13 x 2 = 26e

There are 7 main energy levels, same as the 7 rows in the periodic table. Each level contains a number of sublevels, which are symbolized by the letters listed in the tables above. Each sublevel contains number of orbitals which each contain 2 electrons. The total number of electrons in all of the orbitals equals the total number of electrons for that element. An atom with 6 electrons would have 2 in the first energy level which would be written 1s, 2 in the second energy level 2s and two others in the p orbital which would be written 2p2. This such element is Carbon and has the electron configuration of: 1s 2s 2p2. According to the following diagram, the last orbital places carbon in the p section of the periodic table. Upon inspection of a periodic table, this is proved true.

 

Electron Locator 2n

Quantum Number/Energy Level

Electron Capacity

Sublevel/Orbital

1

2

1s

2

8

2s 2p6

3

18

3s 3p6 3d10

4

32

4s 4p6 4d10 4f14

5

50

5s 5p6 5d10 5f14 5g18

6

72

6s 6p6 6d10 6f14 6g18 6h22

7

98

7s 7p6 7d10 7f14 7g18 7h22 7i26

 

 

 

 

 

The orbitals are known to overlap each other rather than following an orderly fashion. As shown in the diagram above, 4s has a lower energy level than 3d, meaning 3d will be located between 4s and 4p on the energy level ladder. The following poem and diagram show the order of the orbitals in order of increasing energy level, which is the order they will be written in. .

A Q.M. Poem

1s2

2s2 2p6

3s2 3p6

4s2 3d10 4p6

5s2 4d10 5p6

6s2 4f14 5d10 6p6

7s2 5f14 6d10 7p6

 

 

In the ground state of the atom, electrons will occupy the lowest energy orbitals first, and only fill the higher energy orbitals when no lower energy orbitals are left. The arrangement of electrons in an atom is known as its electronic configuration

abbreviate the electron configuration by that of the preceding noble gas. For Mg, this is neon, which has an electron configuration of 1s22s22p6, so we can write the the electron configuration of the Mg atom as Mg: [Ne]3s2

# sublevels = principle quantum number

 

Electrons repel each other, by occupying different orbitals the electrons remain as far as possible from one another.

Link to: http://intro.chem.okstate.edu/WorkshopFolder/Electronconf.html Excellent diagram.

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