Write Lewis structures for the following molecules and ions: (a) \(\mathrm{NCl}_{3},(\mathrm{~b}) \mathrm{OCS},(\mathrm{c}) \mathrm{H}_{2} \mathrm{O}_{2},(\mathrm{~d}) \mathrm{CH}_{3} \mathrm{COO}^{-}\) (e) \(\mathrm{CN}^{-}\) (f) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{3}^{+}\)

Valence electrons are the electrons that reside in the outermost shell of an atom and play a pivotal role in chemical bonding and the properties of molecules. These electrons determine how an atom can bond with others. For instance, the element Nitrogen (N) has five valence electrons, while Chlorine (Cl) has seven.

To determine the number of valence electrons for any given molecule or ion, one must sum up the valence electrons of all the individual atoms.

The octet rule is a chemical rule of thumb that reflects observation that atoms of main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas. The rule is applicable to the main-group elements, especially carbon, nitrogen, oxygen, and the halogens, but is less applicable to metals and elements beyond the second period. Hydrogen is an exception, as it can be considered to be in a stable configuration with only two valence electrons.

When drawing Lewis structures, one of the main goals is to ensure that most atoms (with the noted exceptions) meet this rule. For molecules or ions that don't naturally satisfy the octet rule, adjustments such as the creation of double or triple bonds are sometimes necessary.

The molecular geometry – also known as molecular structure – refers to the three-dimensional arrangement of atoms within a molecule. Determining the arrangement involves not only recognizing the atomic connections but also the electron pairs that do not participate in bonding, known as lone pairs.

The VSEPR (Valence Shell Electron Pair Repulsion) theory is often employed to predict the geometry of molecules. For instance, a molecule with two atom groups (either two bonds or one bond and a lone pair) will exhibit linear geometry, while a molecule with three atom groups with no lone pairs will display a trigonal planar geometry. The electrons' distribution in space ultimately influences the molecular shape, which affects the molecule's physical and chemical properties.