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The bonding electron pair shared in a sigma bond with an adjacent atom lies further from the central atom than a nonbonding (lone) pair of that atom, which is held close to its positively charged nucleus. VSEPR theory therefore views repulsion by the lone pair to be greater than the repulsion by a bonding pair.
Lone pairs (shown as pairs of dots) in the Lewis structure of hydroxide. In science, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bond [1] and is sometimes called an unshared pair or non-bonding pair. Lone pairs are found in the outermost electron shell of atoms.
An equatorial lone pair is repelled by only two bonding pairs at 90°, whereas a hypothetical axial lone pair would be repelled by three bonding pairs at 90° which would make the molecule unstable. Repulsion by bonding pairs at 120° is much smaller and less important. [2] [1]
In Lewis' bonding model, the electrons tend to pair up in bonds such that an atom has a total of four chemical bonds and lone pairs associated with it: thus, the atom can satisfy its octet. LDQ theory also acknowledges that the elements in the ‘first short period’ of the periodic table tend to attain an octet of electrons surrounding them.
In accordance with the VSEPR (valence-shell electron pair repulsion theory), the bond angles between the electron bonds are arccos(− 1 / 3 ) = 109.47°. For example, methane (CH 4) is a tetrahedral molecule. Octahedral: Octa-signifies eight, and -hedral relates to a face of a solid, so "octahedral" means "having eight faces". The bond ...
It enables prediction and explication of molecular geometries that are not necessarily satisfactorily or even correctly explained by semi-empirical theories such as Walsh diagrams, atomic state hybridization, valence shell electron pair repulsion (VSEPR), softness-hardness-based models, aromaticity and antiaromaticity, hyperconjugation, etc. [1]
In the case of water, with its 104.5° HOH angle, the OH bonding orbitals are constructed from O(~sp 4.0) orbitals (~20% s, ~80% p), while the lone pairs consist of O(~sp 2.3) orbitals (~30% s, ~70% p). As discussed in the justification above, the lone pairs behave as very electropositive substituents and have excess s character.
According to the VSEPR model (Valence Shell Electron Pair Repulsion model), linear geometry occurs at central atoms with two bonded atoms and zero or three lone pairs (AX 2 or AX 2 E 3) in the AXE notation.