Final answer:
You find the valency of an element and the chemical formula of a compound by identifying the number of valence electrons an atom has (c). For ionic compounds, you combine ions in ratios that neutralize charge, while for molecules, you add valence electrons from each atom. To balance chemical equations, you ensure each element's atoms are equal on both sides of the reaction.
Step-by-step explanation:
To find the valency and chemical formula of a compound, you must identify the number of valence electrons. The valency of an element is determined by its ability to combine and form chemical bonds, often indicated by the number of valence electrons it has. The valency is critical in understanding how atoms will combine to form molecules and compounds.
When writing the chemical formula for a binary ionic compound, for example, you take the metal ion with its charge and pair it with the nonmetal ion with its charge. Ensuring the total charges are neutralized, you determine how many ions of each type are needed to achieve electrical neutrality. For molecules or polyatomic ions, you add together the valence electrons from each atom (or add/subtract electrons if it's an ion).
To balance a chemical equation, you begin with the correct formulas for reactants and products and use a trial-and-error method to ensure each element appears in the same number on both sides of the equation. You balance polyatomic ions as a unit and adjust coefficients to ensure that the atoms of each element are equal on both sides. The aim is to have coefficients in the lowest possible ratio.