Phosphorus (P) and bromine (Br) form a compound. Predict the formula of this compound starting with dot diagrams for the atoms.

Lewis structures, also known as Lewis dot diagrams, are graphical representations of molecules that show the bonds between the atoms and the arrangement of valent electrons. In constructing a Lewis structure, the valence electrons are represented as dots placed around the chemical symbols of the elements involved.

For instance, when predicting the formula of a compound formed by phosphorus (P) and bromine (Br), we begin by representing phosphorus with five dots, since as a group 15 element, it has five valence electrons. Similarly, bromine, a group 17 element, is surrounded by seven dots. These dot diagrams help to visualize how atoms can share electrons to form covalent bonds, aiming to achieve a stable octet configuration, similar to noble gases.

Valence electrons are the electrons located in the outermost shell of an atom that are available for forming chemical bonds with other atoms. These electrons play a crucial role in chemical reactions and determine the bonding capacity of the element.

In our example, phosphorus has five valence electrons, while bromine has seven. Understanding the number of valence electrons is essential for predicting how atoms will bond. Atoms typically seek to fulfill the ‘octet rule’, where they prefer to have eight electrons in their valence shell. This can be achieved through the transfer or sharing of electrons, resulting in ionic or covalent bonds, respectively.

Covalent bonds are formed when two atoms share pairs of electrons in order to achieve a complete outer shell of electrons. It's one of the strongest types of chemical bonds and forms between non-metal atoms with similar electronegativities.

In the phosphorus and bromine example, each phosphorus atom shares one of its valence electrons with three bromine atoms to form covalent bonds. This sharing allows each bromine atom to fill its last remaining spot for an octet, and the phosphorus atom also achieves an octet. Covalent bonding, as seen in the formation of PBr₃, involves the mutual sharing of electrons and leads to the creation of stable molecules.

The molecular formula of a compound gives us concise information about the types and numbers of atoms present in a molecule. It reflects the actual number of atoms of each element that are bonded together to form the molecule.

For the compound created by phosphorus and bromine, the molecular formula is PBr₃, which means there is one phosphorus atom covalently bonded to three bromine atoms. Molecular formulas are crucial for understanding the composition of a molecule and for further analysis of its properties and behaviors in chemical reactions.