for an orbital, the lower is its energy. If two orbitals have the same ( n + l ) value, the orbital with lower value of n has the lower energy. In an atom many such orbitals are possible and electrons are filled in those orbitals in order of increasing energy in accordance with Pauli exclusion principle (no two electrons in an atom can have the same set of four quantum numbers) and Hund’s rule of maximum multiplicity (pairing of electrons in the orbitals belonging to the same subshell does not take place until each orbital belonging to that subshell has got one electron each, i.e., is singly occupied). This forms the basis of the electronic structure of atoms.
EXERCISES . (i) Calculate the number of electrons which will together weigh one gram. (ii) Calculate the mass and charge of one mole of electrons. .
(i) Calculate the total number of electrons present in one mole of methane. (ii) Find (a) the total number and (b) the total mass of neutrons in mg of 14C. (Assume that mass of a neutron = . × – kg).
(iii) Find (a) the total number and (b) the total mass of protons in mg of NH at STP. Will the answer change if the temperature and pressure are changed ? . How many neutrons and protons are there in the following nuclei ?
C O Mg Fe Sr , , , , . Write the complete symbol for the atom with the given atomic number (Z) and atomic mass (A) (i) Z = , A = . (ii) Z = , A = . (iii) Z = , A = .
. Yellow light emitted from a sodium lamp has a wavelength ( λ ) of nm. Calculate the frequency ( ν ) and wavenumber ( ) of the yellow light. .
Find energy of each of the photons which (i) correspond to light of frequency × Hz. (ii) have wavelength of . Å. .
Calculate the wavelength,