chemistry

 ATOMIC STRUCTURE IMPORTANT POINTS

:1. Electrons, protons and neutrons are called sub-atomic particles.
2. J.J. Thomson's atomic model could not explain the atomic spectra.
3. Rutherford proposed "Planetary atomic model" based on á-ray scattering
experiments.

4. According to this model, electrons are subjected to two types of forces that is
1) The force of attraction between electrons and the nucleus

2) The centrifugal force
These two forces are equal and opposite.
5. Max Planck proposed the Quantum theory of radiation.
6. E = hí Planck's constant h = 6.625 × 10–27 erg.sec. (or) 6.625 × 10–34 J.sec.
7. Bohr proposed his atomic model based on Planck's Quantum theory.
8. Bohr model explains stationary orbits, angular momentum and radiation of energy.
9. Bohr model could not explain the atomic spectra of higher elements, Zeeman effect,
quantization of angular momentum.
10. Sommerfeld proposed the elliptical orbits and sub-stationary states.
11. Orbits are indicated by "Principal Quantum number" ie 'n', sub-stationary states are
indicated by "Azimuthal Quantum number i.e 'l', orientation of orbitals is indicated by
"magnetic Quantum number" i.e, 'm' and spinning of electrons of "Spin Quantum
number" 's'.
12. l value = (n – 1), the number of 'm' values is equal to (2l + 1) and ranges from
–l....0....+l. s is +1/2 or –1/2.13. "The region in space where there is finite probability of finding electron" is called
"atomic orbital".
14. s, p, d and f orbitals are present in the orbits. 1, 2, 3 and 4 onwards (or) K, L, M and
N onwards successively.
15. Orbitals having same energy are called degenerate orbitals.
16. "Electron occupies the orbital whose (n + l) value is minimum. If (n + l) value is same,
it occupies the orbital having less 'n' value" ____ Aufbau Principle.
17. "No two electrons will have all the four Quantum numbers same" ___ Pauli exclusionprinciple.
18. "Pairing of electrons takes place when all the degenerate orbitals are occupied by one
electron each" ____ Hund's rule.
19. Atomic radius is the distance between the nucleus and outermost orbital.
Units: A° ; 1A° = 10–8 cm or 10–10m.
20. Ionization potential is "the minimum energy required to remove an electron from
outermost orbital in the gaseous state".
Units: ev (or) K.J. mol–1 (or) K.Cal.mol–1.
21. Electron affinity is "the energy released when an electron is added to a neutral
gaseous atom in the ground state".
Units: ev (or) K.J. mol–1 (or) K.Cal.mol–1.