Statement 1 Alkyl carbanion such as \(\mathrm{CH}_{3}^{-}\) has pyramidal shape. and Statement 2 The carbon atom carrying the negative charge has an octet of electrons.

In understanding alkyl carbanions, a common example is \(\mathrm{CH}_{3}^{-}\), a molecule with a fascinating three-dimensional shape known as pyramidal geometry. Geometric shapes in molecules occur due to the way atoms and their accompanying electrons arrange themselves to minimize repulsion. In a pyramidal structure, the central atom—carbon, in this case—bonds to three other atoms, forming the base of a pyramid, while also having a lone pair of electrons at the apex.

This geometry is similar to that seen in ammonia (NH3), where the lone pair pushes the hydrogen atoms downwards, creating a non-planar molecule. This repulsion results in bond angles that are slightly less than the typical tetrahedral 109.5 degrees; in the case of \(\mathrm{CH}_{3}^{-}\), this subtle change gives rise to its characteristic three-dimensional structure.

The octet rule is a fundamental concept in chemistry, dictating that atoms tend to form bonds to have eight electrons in their valence shell, bringing them to a state of higher stability similar to noble gases. For \(\mathrm{CH}_{3}^{-}\), the carbon atom achieves this stable electron configuration by sharing electrons with three hydrogen atoms and possessing a lone pair of electrons.

The sharing of electrons through covalent bonding with hydrogen atoms contributes three electrons to carbon's valence shell, while the lone pair contributes two more electrons (as a pair counts as two), thus fulfilling the octet rule. Because the carbon atom has a total of four valence electrons initially, the additional four from the bonds and the lone pair bring the total to eight, satisfying the conditions of the octet rule and lending stability to the carbanion.

Alkyl carbanions, including species like \(\mathrm{CH}_{3}^{-}\), carry a negative charge on the central carbon atom. This charge is crucial to the molecule's chemical behavior and reactions. A negatively charged carbon atom indicates that an extra electron is present, resulting in a total of five valence electrons around the carbon. Three of these electrons are shared with hydrogen atoms to form covalent bonds, and the two remaining electrons form a lone pair.

This discrepancy between the number of protons in the carbon nucleus and the number of surrounding electrons results in an overall negative charge. This characteristic charge can make alkyl carbanions quite reactive and a key intermediate in many organic reactions. It is this negative charge that often determines the direction and type of chemical reactions in which the carbanion will participate.

A lone pair of electrons is a pair of valence electrons that are not participating in bonding but instead belong exclusively to a single atom. In \(\mathrm{CH}_{3}^{-}\), the carbon atom possesses such a lone pair of electrons. This pair plays a vital role in the molecule's geometry and reactivity.

The presence of this nonbonded electron pair contributes to the pyramidal shape of the alkyl carbanion as exerts repulsion against the bonded electron pairs, leading to the distortion from a perfect tetrahedral shape. In addition, lone pairs are often regions of high electron density and can be sites where chemical reactions, such as nucleophilic attacks, are initiated. Understanding the behavior of lone pairs is thus critical in predicting the reactivity and interaction of molecules like alkyl carbanions.