The statement that the four valence electrons of oxygen form an almost linear arrangement refers to the electron-pair geometry in the oxygen molecule.
Oxygen (O) has six valence electrons, and in its ground state, it forms a double covalent bond with another oxygen atom, resulting in the formation of an oxygen molecule (O₂). Each oxygen atom contributes two electrons to the shared bond, giving a total of four valence electrons involved in bonding.
In the Lewis dot structure of O₂, the four valence electrons are represented by two pairs of electrons (known as a double bond) between the oxygen atoms. This arrangement can be visualized as two electron pairs repelling each other in three-dimensional space.
According to VSEPR theory (Valence Shell Electron Pair Repulsion theory), electron pairs (both bonding and non-bonding) repel each other and tend to position themselves as far apart as possible to minimize repulsion. In the case of O₂, the repulsion between the electron pairs pushes them towards opposite sides, resulting in an almost linear arrangement.
However, it's important to note that the actual bond angle in O₂ is slightly less than 180 degrees (linear) due to the presence of lone pairs of electrons on each oxygen atom. These lone pairs create additional electron-electron repulsions, causing a slight deviation from a perfect linear arrangement.