Chemistry

Octet Theory


The octet theory is based on the stability of the noble gases. Of all the elements that exist in nature, only noble gases can be found free in the form of an isolated atom. The others are connected to each other in different ways and in various combinations.

Noble gases are isolated because they obey the octet rule, that is, they contain eight electrons in their valence shell, or outermost layer, farther from the nucleus, except for Helium, which has two electrons and is stable.

Octet Rule - Chemical elements must always contain 8 electrons in the last electronic layer or valence layer. In the K layer there can be a maximum of 2 electrons. In this way the atoms are stable with the same configuration as the noble gases.

Note the electronic distribution of the noble gases in the following table:

ELEMENT

Z

SYMBOL

K

L

M

N

O

P

Q

Helium

2

He

2

-

-

-

-

-

-

Neon

10

Huh

2

8

-

-

-

-

-

Argon

18

Air

2

8

8

-

-

-

-

Krypton

36

Kr

2

8

18

8

-

-

-

Xenon

54

X and

2

8

18

18

8

-

-

Radon

86

Rn

2

8

18

32

18

8

-

The stability of the noble gases is due to the fact that they have the last complete layer, that is, with the maximum number of electrons this layer can contain while the last one.

Atoms of other chemical elements, in order to be stabilized, must acquire, through chemical bonds, electrospheres equal to those of noble gases.

There are three types of chemical bonds:

- Ionic bond - loss or gain of electrons
- Covalent bond - electron sharing (normal or dative)
- Metal connection - neutral atoms and cations dipped in an "electronic cloud" or "sea of ​​electrons".

These types of calls are called intramolecular bonds, because they happen outside the molecule.

The bonds that happen inside the molecule are called intermolecular bonds or interactions, which are the hydrogen bridges, London forces and dipole dipole.

Summing up:

INTRAMOLECULAR CONNECTION

- ionic
- covalent (normal or dative)
- metallic

INTERMOLECULAR CONNECTION

- hydrogen bridges
- London forces, induced dipole or Van der Waals forces
- dipole dipole or permanent dipole