NEET Chemistry Some Basic Concepts in Chemistry

• Law of conservation of mass: Matter can neither be created nor be destroyed.
• Law of definite proportions: given compound always contains the same proportion of elements by weight.
• Law of multiple proportions: If two elements can combine to form more than one compound, the masses of one element which
  combine with a fixed mass of the other element are in the ratio of small whole numbers.
• Gay-Lusaac’s law of gaseous volumes: When gases combine or are produced in a chemical reaction, they do so in a simple ratio by volume provided all gases are at the same temperature and pressure.
• Avogadro’s law: Equal volumes of gases at the same temperature and pressure should contain equal number of molecules.

• One atomic mass is defined as mass exactly equal to 1/12th the mass of one carbon-12 atom.

• Molecular mass is the sum of atomic masses of the element present in the molecule.

• The formula mass of a molecule is the sum of the atomic weights of the atoms in the empirical formula of a compound.

Mole

• One mole is the amount of substance which contains as many particles or entities as there are atoms in exactly 12 g of the C-12 isotope.

• An empirical formula represents the simplest whole number ratio of various atoms present in a compound.
• A molecular formula shows the exact number of different types of atoms present in a molecule of a compound.