Atoms and Molecules
* Matter is made of tiny indivisible particles.
* In any chemical reaction, the total mass of the substance before and after the reaction is the same although its matter undergoes a physical change.
* Molecule is the combined state of atoms.
* Number of atoms constituting a molecule is atomicity.
* Cation is a positively charged particle in a molecule.
* Negatively charged particle in a molecule is known as anion.
* Combining capacity of an element is known as valency.
* Formula is a short hand representation of a molecule.
* For writing a formula a set of rules are followed.
Mole Concept
* The value of the particles present in one mole of any substance = 6.022 x 1023.
* This is called Avogadro’s number or Avogadro’s constant.
* A mole is a unit used to count the number of particles in a substance.
* The atomic mass of an element is the mass of one atom of that element in atomic mass units (u).
* The molar mass of an element is equal to the numerical value of the atomic mass.
* However, in case of molar mass, the units change from ‘u’ to ‘g’.
* The sum of the atomic masses of all the atoms in a molecule of a substance is called the molecular mass.
* The formula unit mass of a substance is the sum of the atomic masses of all atoms in a formula unit of a compound.
