Buy BOOKS at Discounted Price

Atoms And Molecules

What you will learn

  • During a chemical reaction, the sum of the masses of reactants and products remains unchanged. This is known as the Law of Conservation of Mass.

  • In a pure chemical compound, elements are always present in a definite proportion by mass. This is known as the Law of Definite Proportions.

  • An atom is the smallest particle of an element that cannot usually exist independently and retain all its chemical properties.

  • A molecule is the smallest particle of an element or a compound capable of independent existence under ordinary conditions. It shows all the properties of the substance.

  • A chemical formula of a compound shows its constituent elements and the number of atoms of each combining element.

  • Clusters of atoms that act as an ion are called polyatomic ions. They carry a fixed charge on them.

  • The chemical formula of a molecular compound is determined by the valency of each element.

  • In ionic compounds, the charge on each ion is used to determine the chemical formula of the compound.

  • Scientists use the relative atomic mass scale to compare the masses of different atoms of elements. Atoms of carbon-12 isotopes are assigned a relative atomic mass of 12 and the relative masses of all other atoms are obtained by comparison with the mass of a carbon-12 atom.

  • The Avogadro constant 6.022 × 1023 is defined as the number of atoms in exactly 12 g of carbon-12.

  • The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon-12.

  • Mass of 1 mole of a substance is called its molar mass.