Upload
gurudatta-wagh
View
149
Download
0
Embed Size (px)
Citation preview
Standard/ Class/ Grade XI ChemistryChapter 1 Basic ConceptsGurudatta K Wagh, [email protected]
Isotopes, Atomic mass, Molecular mass
Isotopes
Atoms of the same elements having same atomic number containing same number of protons and electrons but different number of neutrons
Have different mass numbers
Hydrogen – Three isotopes, H-1 (protium 1H, 1 proton and no neutron, 99.98 %), H-2 (1 proton and 1 neutron) (deuterium 2H), H-3 (tritium 3H) (1 proton and 2 neutrons), observed atomic mass 1.008 u
Neon-20 (19.9924 u), Ne-22 (21.9914 u), Ne-21 (20.9940 u). Average atomic mass of Ne = 20.1707 u
Observed atomic mass is the average atomic mass taking into consideration the natural abundance (per cent occurrence) of the isotopes
Atomic mass
Masses of atoms of elements is determined relative to mass of a standard
Carbon-12 is chosen as standard
Atomic mass unit (amu) or unified mass (u) of carbon is 12
Masses of other atoms are determined relative to the mass of an atom of carbon-12
Carbon-12 (98.89 %), C-13, C-14 are the three isotopes of carbon
Atomic mass unit (amu) or unified mass (u) of carbon is 12
Masses of other atoms are determined relative to the mass of an atom of Carbon-12
Molecular/ molar mass
Relative mass compared to mass of standard atom of Carbon-12
Ratio of mass of one molecule of a substance to 1/12th of mass of one atom of Carbon-12
Algebraic sum of atomic masses of constituent atoms
Unitless quantity
Molar mass expressed in gram is gram molar mass
1 gram molar mass = 1 gram molecule = 1 mole = 1 gram atom
It is calculated as the sum of the atomic mass of each constituent atom multiplied by the number of atoms of that element in the molecular formula
Molecular mass or molecular weight is the mass of a molecule. The adjective 'relative' is omitted as it is universally assumed that atomic and molecular masses are relative to the mass of 12C