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A Lewis dot diagram is a visual representation of the valence electrons in an atom or molecule. It is a straightforward method to depict the location of electrons around the atomic symbols, with dots representing valence electrons. For molecules, the diagram shows how atoms bond and whether any lone pairs of electrons exist.

For example, in the case of selenium hexafluoride (SeF₆), the Lewis dot diagram illustrates selenium at the center with six fluorine atoms bonded to it, while also depicting the electron pairs that are not involved in bonding – known as lone pairs. The exercise shows how to build this visualization step by step, catering to both the central and surrounding atoms until a complete picture of the molecule's electron distribution is achieved.

Valence electrons are the electrons in the outermost shell of an atom that participate in chemical bonding. They determine an atom's chemical properties and its ability to form bonds. In the selenium hexafluoride example, we calculate the valence electrons for selenium and fluorine based on their group numbers in the periodic table.

Valence electrons are critical as they are involved in the formation of chemical bonds. These electrons follow the octet rule, which states that atoms tend to bond in such a way that each atom has eight electrons in its valence shell, creating a stable electronic configuration similar to that of the noble gases.

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is influenced by the number of bonds and lone pairs around the central atom. VSEPR theory (Valence Shell Electron Pair Repulsion theory) helps predict the shape of a molecule based on the repulsion between electron pairs.

In selenium hexafluoride, the molecule takes on an octahedral shape since there are six regions of electron density surrounding the selenium atom, due to its six bonds with fluorine atoms. The molecular geometry is an integral aspect of understanding how a molecule will behave in various chemical reactions.

Chemical bonding is the process by which atoms combine to form molecules through the sharing or transfer of valence electrons. There are primarily three types of chemical bonds: ionic, covalent, and metallic. In the SeF₆ example, the selenium and fluorine atoms form covalent bonds, where they share electrons to fulfill the octet rule as closely as possible.

However, selenium hexafluoride is an example of an exception to the octet rule, demonstrating that not all elements adhere strictly to it. Instead, selenium uses its d-orbitals to form 'expanded octets,' allowing for more than eight electrons in its valence shell. This capability to hold extra electrons is vital for the formation of certain types of chemical compounds and is a fascinating part of the study of chemical bonding.