Which of the following is produced, when copper reacts with chlorine? (a) \(\mathrm{CuCl}_{4}\) (b) \(\mathrm{Cu}_{2} \mathrm{Cl}\) (c) \(\mathrm{Cu}_{2} \mathrm{Cl}_{2}\) (d) \(\mathrm{CuCl}_{2}\)

Valency is a fundamental concept in chemistry that indicates the combining power of an element, particularly how many electrons an atom can lose, gain, or share to form stable chemical bonds. For example, the valency of hydrogen is +1, meaning it can form bonds by sharing or transferring one electron. Similarly, oxygen has a valency of -2, meaning it typically forms bonds by accepting two electrons.

In constructing chemical formulas, valency plays a pivotal role. It allows chemists to determine the proportions in which atoms combine to form compounds. The rule of thumb is that the total positive charge (+) should balance the total negative charge (-) in a compound. To write the chemical formula, you cross over the valency of one element to become the subscript of the other element, and vice versa. If we take sodium chloride (NaCl) as an example, sodium (Na) has a valency of +1 and chlorine (Cl) has a valency of -1. When these two elements combine, they form a 1:1 ratio compound, resulting in the formula NaCl.

Copper chloride formation is a typical chemical reaction involving the transition metal copper (Cu) and the halogen element chlorine (Cl). As we delve into the specifics, copper, which generally has a valency of +2, reacts with chlorine, which has a valency of -1, to form a compound. The valency indicates that one copper atom can combine with two chlorine atoms to form a neutral compound. Copper chloride can exist in different forms depending on the hydration state but the anhydrous form, in particular, is CuCl2.

When copper reacts with chlorine gas, the copper atoms donate one electron to each of the two chlorine atoms, satisfying the octet rule for the chlorine atoms and allowing the copper atom to achieve a stable electron configuration. The reaction is an example of a redox process where copper is oxidized and chlorine is reduced. In this specific chemical reaction, the formation of CuCl2 represents a direct combination reaction, where elements combine to form a more complex product.

Balancing chemical equations is crucial for correctly representing chemical reactions. It is a method of ensuring that the Law of Conservation of Mass is adhered to, which posits that matter cannot be created or destroyed in a chemical reaction. Therefore, the quantity of each element must be the same on the reactant side as on the product side of the equation.

To balance a chemical equation, first, write down the unbalanced equation showing the reactants and products. Then, adjust the coefficients – the numbers placed before the chemical formulas – to achieve the same number of atoms for each element on both sides. For instance, the reaction of hydrogen (H2) and oxygen (O2) to form water (H2O) starts out unbalanced as \(H_2 + O_2 \rightarrow H_2O\). After balancing, it becomes \(2H_2 + O_2 \rightarrow 2H_2O\), indicating that two molecules of hydrogen react with one molecule of oxygen to form two molecules of water.

A balanced chemical equation ensures that all atoms are accounted for, allowing chemists to predict the quantities of reactants needed and the amount of products formed in a chemical reaction.