# Chemistry: Atom Molecules Arithmetic: Empirical and Molecular Formula

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## Empirical and Molecular Formula Image of Empirical and Molecular FormulaImage of Empirical and Molecular Formula
• The Empirical formula is defined as the simplest positive integer ratio of atoms present in a compound. For example the empirical formula of disulphur dioxide is .

• The Molecular formula is defined as formula that expresses of the number of atoms of each element in one molecule of a compound. This formula shows the actual number of each atom in a molecule. For example the molecular formula for water is

## Mole, Mass, Volume Relationship

• A mole of a substance is defined as: The mass of substance containing the same number of fundamental units as there are atoms in exactly 12.000 g of. Fundamental units may be atoms, molecules, or formula units, depending on the substance concerned.

• Mass is a measure of the amount of matter in an object.

• Mass is usually measured in grams (g) or kilograms (kg). An object’s mass is constant in all circumstances; contrast this with its weight, a force that depends on gravity. Your mass on the earth and the moon are identical.

• Volume is the quantity of three-dimensional space occupied by a liquid, solid, or gas. Common units used to express volume include liters, cubic meters, gallons, milliliters, teaspoons, and ounces, though many other units exist.

## Stoichiometry and Calculations Based on Stoichiometry

• Stoichiometry expresses the quantitative relationship between reactants and products in a chemical equation. Stoichiometric coefficients in a balanced equation indicate molar ratios in that reaction. Stoichiometry allows us to predict certain values, such as the percent yield of a product or the molar mass of a gas.

• Thus, to calculate the stoichiometry by mass, the number of molecules required for each reactant is expressed in moles and multiplied by the molar mass of each to give the mass of each reactant per mole of reaction. The mass ratios can be calculated by dividing each by the total in the whole reaction.

## Limiting Reagent Concept and Percentage Yield

The limiting reactant (or limiting reagent) is the reactant that determines the amount of product that can be formed in a chemical reaction. The reaction proceeds until the limiting reactant is completely used up. In our example above, is the limiting reactant.

## Atoms, Molecules and Elements

• An atom of one element is different in size and mass from the atoms of the other elements.

• Atoms can be broken down into still smaller particles although they lose their chemical identity in this process.

• A molecule is an aggregate of at least two atoms in a definite arrangement held together by chemical forces (also called chemical bonds).

• It is smallest particle of matter, an element or a compound, which can exist independently. A molecule may contain atoms of the same element or atoms of two or more elements joined in a fixed ratio, in accordance with the law of definite proportions stated.

• For e.g. Hydrogen Gas is pure element consists of molecules made up of two H atoms each. Water, on the other hand, is a molecular compound that contains hydrogen and oxygen in a ratio of two H atoms and one O atom. Like atoms, molecules are electrically neutral.Is a diatomic molecule.

• An element is a substance that cannot be separated into simpler substances by chemical means. Till date 118 elements have been positively identified, 83 of them occur naturally on Earth. Others have been created by scientists via nuclear processes.