Final answer:
LiF is an ionic compound with a 1:1 ratio of lithium cations to fluorine anions to achieve electrical neutrality. The size difference between cations and anions is due to changes in electron-electron repulsion when electrons are added or removed. This principle of charge balance applies to all ionic compounds for them to be neutral and stable.
Step-by-step explanation:
LiF, which is lithium fluoride, is an ionic compound that represents the simplest whole-number ratio between cations and anions to form a neutral molecule. In the case of LiF, lithium (Li) acts as the cation with a 1+ charge, and fluorine (F) acts as the anion with a 1- charge. The sizes of these ions are influenced by their electron configurations: a cation is smaller compared to its parent atom because removing an electron reduces electron-electron repulsion and the size of the electron cloud. Conversely, an anion is larger than its parent atom due to the addition of an electron, which increases electron-electron repulsion and expands the electron cloud.
To form a neutral ionic compound, LiF requires a 1:1 ratio of lithium to fluorine, meaning one lithium cation combines with one fluorine anion. This simple ratio is a result of each ion having a single charge, balancing out to create an electrically neutral compound. This balance is a guiding principle for all ionic compounds where the total positive charge must equal the total negative charge to achieve neutrality. For example, calcium chloride (CaClâ‚‚) forms with two chloride anions for every calcium cation to maintain electrical neutrality. In LiF, the small size of ions and the high charge density contribute to its large lattice energy and high melting and boiling points, making it a very stable ionic compound.