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As such, when a molecule has 2 interactions with different degrees of repulsion, VSEPR theory predicts the structure where lone pairs occupy positions that allow them to experience less repulsion. Lone pair–lone pair (lp–lp) repulsions are considered stronger than lone pair–bonding pair (lp–bp) repulsions, which in turn are considered ...
The seesaw geometry occurs when a molecule has a steric number of 5, with the central atom being bonded to 4 other atoms and 1 lone pair (AX 4 E 1 in AXE notation). An atom bonded to 5 other atoms (and no lone pairs) forms a trigonal bipyramid with two axial and three equatorial positions, but in the seesaw geometry one of the atoms is replaced ...
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.
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.
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]
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.
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.
2 O reveals four different energy levels that correspond to the ionization energies of the two bonding and two nonbonding pairs of elections at 12.6eV, 14.7eV, 18.5eV, and 32.2eV. [1] This suggest that neither the two O-H bonds nor the two sp 3 lone pairs are degenerate in energy.