Hund’s rule and Ionization potential and Electron affinity and Electronegativity

Hund’s Rule

·      Hund’s rule of maximum multiplicity states that electron pairing takes place only after all the available degenerate orbitals are occupied by one electron each.
Ex: Carbon atom (At.No.: 6)
·      Carbon atom has six electrons
·      The first electron goes into the ‘1s’ orbital of k-shell.
·      The second electron will be paired up with the first in the same ‘1s’ orbital.
·      Similarly the third and fourth electrons occupy the ‘2s’ orbital of the L-shell.
·      The fifth electron goes into one of the three ‘2p’ orbitals of L-shell. (2Px)
·      Since the three ‘p’ orbitals (2Px, 2Py, 2P3 are degenerate) the sixth electron goes into 2Py or 2Pz but not 2Px



IONIZATION POTENTIAL or IONIZATION ENERGY

·      Definition : “Ionization energy or Ionization potential is defined as the minimum energy required to remove an electron from the outermost orbital of an atom in the gaseous state.”
·      Expressed in units of electron volt or K.J.Mole-1 



·      Ionization potential is dependent on
1) Nuclear charge
2) Size of the atom
3) Charge on the ion
4) Half filled and fully filled orbitals
·      In general ionization energy increases across a period, because of decrease in the atomic size
·      In a group ionization energy decreases from top to bottom because atomic radius increases.

ELECTRON AFFINITY

Definition:Electron affinity is defined as the energy released when an electron is added to a neutral gaseous atom in its lowest energy state
·      Expressed in electron volt (eV)
·      Halogens have high values of electron affinity
·      The electron affinity for halogens follows the order of
·      Cl > F> Br > I
·      In a group, the electron affinity decreases from top to bottom as the atom size increases
·      In a period the electron affinity increases from left to right.

ELECTRO NEGATIVITY (E.N) 

Definition: Electro negativity is defined as the tendency of bonded atom in a molecule to attract the electron density of the shared pair of electrons.
·      Small size atoms have more tendency to attract the shared electron density and hence to attract the shared electron density and hence have larger EN values.
·      In a period, the electro negativity increases due to the decrease in size of atom
·      In a group the electro negativity decreases due to increase in atomic size.
·      Fluorine has been assigned a value of 4.0 for electro negativity in the Pauling scale. 



Comments

Post a Comment

Popular posts from this blog

pneumatic comparator and solex pneumatic comparator

Image
Principle of pneumatic comparator The measurement is made by taking reading using master gauge of known accuracy and comparing with component reading It uses a controlled, pressurised jet of air to measure small dimensional variation in the size of component The working principle of pneumatic comparator depends on the flow of air between the gauge head and the component being checked Important characteristics Very high magnifications are possible It can be used to measure diameters, length, squareness, parallelisms, concentricity,taper, and other geometric conditions. Internal dimensions can be readily measured , in other words, while measuring a bore it can reveal complete details of size, taper, straightness,camber and bell mouth etc. It is independent of the operator skill High pressure air gauging can be done by cleaning the parts which helps to eliminate errors due to dirt and foreign matter. As there is no physical contact made either with the setting gauge (or)
All Blog Posts

surface roughness and straightedge surfaceplate surface gauge visual inspection profilometer opticalflat

Image
Surface roughness On any finished surface,imperfections are found and these take the form of a succession of hills and valleys Which vary both in height and in spacing and result in a kind of texture which in appearance or feel. Straight edge Straightedges are commonly used for testing the straightness and flatness of plane surfaces Flatness is checked by a light test The narrow edge of the tool is applied to the surface to be tested and kept horizontally at the eye level Watching for light between the straightedge and the surface along the straightedge Light seen at one place or another indicates deviation from straightness Surface plate Surface plate is used for testing the flatness of work itself and is also used for marking out work This is used for small pieces of work while the marking -out table is used for larger jobs It is used in conjunction with other gauges,the plate becomes a functional gauge in itself. Surface gauge Surface gauge is used in lay
All Blog Posts

Autocollimator and tool makers micro scope

Image
Autocollimator The autocollimator is an optical instrument and is used to measure angular displacements with high accuracy of 0.2 seconds arc It can also be used to measure the flatness of a large surface Collimation of light If a point source of light is placed at the focal point of convex lens ,parallel rays of light are reflected by the lens. This is known as collimation of light A device with a lens suitable for causing light rays from a point source to become parallel is known as a collimato r Auto collimation of light Auto collimation of light occurs when reflecting surface is used in conjunction with a collimation lens system The collimation rays will be reflected back from the surface These rays pass through lens ,and unless reflecting surface is perfectly tangential to the lens axis ,will be brought to a focus along side of the light source Principle of the autocollimator From the fig. The light in the form of parallel rays , i
All Blog Posts