Write the Lewis structure of (a) \(\mathrm{OCl}_{2}\); (b) \(\mathrm{PBr}_{3}\); (c) \(\mathrm{GeH}_{4}\); (d) \(\mathrm{GaCl}_{3}\)

Valence electrons are the electrons in the outermost shell of an atom, which are responsible for the chemical properties of the element. These electrons are the ones involved in forming bonds with other atoms to create chemical compounds. The number of valence electrons can usually be identified by the group number of the element in the periodic table. For example, oxygen is in group 16 and has 6 valence electrons, while chlorine, found in group 17, has 7 valence electrons.

In our exercise, calculating the total number of valence electrons is the first step to drawing Lewis structures. For instance, in the compound OCl₂, oxygen's 6 valence electrons and chlorine's 7 valence electrons add up to a total of 20 valence electrons that must be accounted for in the structure.

The octet rule is a fundamental concept in chemistry that dictates atoms tend to form bonds in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. This rule applies to most elements, except for hydrogen, which seeks to fill its valence shell with only 2 electrons (the duet rule).

When you're drawing Lewis structures, the octet rule helps us determine how atoms share electrons. In cases like GeH₄, Ge achieves the octet rule by forming single bonds with four hydrogen atoms. However, some elements, like phosphorus in PBr₃, can have more than eight electrons around them, which is known as the expanded octet. Gallium in GaCl₃ typically has less than an octet, illustrating exceptions to the octet rule.

Chemical bonding is the process by which atoms join together to form compounds. These bonds result from the attraction between the positively charged nuclei of atoms and the negatively charged electrons they share. The most common types of chemical bonds include ionic, covalent, and metallic bonds.

The Lewis structures deal primarily with covalent bonds, where atoms share valence electrons to achieve full valance shells, often guided by the octet rule. For instance, in the molecules OCl₂ and PBr₃, we see single bonds representing the sharing of a pair of electrons between two atoms. The exercise we're exploring requires a thorough understanding of how these bonds are formed and represented to determine the stability of the molecules and how they might interact with other substances.