Write Lewis structures for the following molecules or ions: (a) \(\mathrm{SbH}_{3}\) (b) \(\mathrm{XeF}_{2}\) (c) \(\mathrm{Se}_{8}\) (a cyclic molecule with a ring of eight Se atoms)

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding because they can be gained, lost, or shared to create chemical compounds. For example, in the molecule SbH3, antimony (Sb) has 5 valence electrons, while each hydrogen (H) has 1 valence electron. Knowing the number of valence electrons helps predict how atoms will bond with each other.

To locate valence electrons using the periodic table, find the element's main group number. For instance, Group 1 elements have 1 valence electron, while Group 17 elements have 7. Transition metals are trickier as their valence electrons can vary. Understanding valence electrons is essential, as it also influences the reactivity and properties of the elements.

Chemical bonding is the process by which atoms combine to form new substances, and it occurs when atoms exchange or share valence electrons. There are three main types of chemical bonds: ionic, covalent, and metallic. Ionic bonds form between metals and non-metals as electrons are transferred. Covalent bonds, such as those in SbH3 and Se8, occur when atoms share valence electrons. Lastly, metallic bonds are specific to metals where electrons are shared in a 'sea' of delocalized electrons.

For instance, in XeF2, Xenon (Xe) forms covalent bonds with fluorine (F) atoms. The ability to understand and predict how atoms will combine lies in examining the number and arrangement of valence electrons, directly influencing the resulting molecular structure and properties.

The octet rule is a chemical rule of thumb that states atoms tend to bond in such a way that they each have eight electrons in their valence shell, giving them the same electron configuration as a noble gas. Hydrogen is an exception as it seeks to have two electrons. The octet rule helps explain the stability of many molecules, such as why Se8 forms a ring structure where each Se atom shares two electrons to complete its octet.

However, there are exceptions like Xenon in XeF2, where Xenon has more than eight valence electrons, which is an example of the 'expanded octet'. The octet rule is critical for predicting the structure of molecules and their reactivity. It is a fundamental principle that students must understand to grasp the basics of chemical bonding.

Electron distribution refers to how electrons are spread out around an atom or within a molecule. For Lews structures, electron distribution dictates where valence electrons are located, whether in lone pairs, bonding pairs, or in some cases, multiple bonds. With SbH3, all valence electrons are used to form single bonds with Hydrogen, adhering to the octet rule for Hydrogen. In XeF2, we distribute lone pairs to satisfy the expanded octet rule for Xe, an example of an exception to the typical octet rule.

When drawing Lewis structures, it's important to accurately represent electron distribution, as it influences molecular shape, reactivity, and the overall stability of the compound. Counts of bonding and non-bonding electrons will dictate the final arrangement of atoms in a molecule.