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Important Chemical Terms - 2

ATOMIC STRUCTURE

· HUND?S RULE: when several orbital of the same type are available, the electrons 1^st fill at the orbitals of same energy singly with parallel spins b4 pairing in any orbital takes place.

· INFRARED RADIATION: electromagnetic radiations possessing wavelength b/w those of visible light nd those of radio waves, i.e;frm approximately 10^-4to 7x10^-7 m

· ISOTOPES: atoms having the same nuclear charge, but different numbers of neutrons in their nuclei.

· MAGNETIC QUANTUM NO: denotes the orbital an electron occupies within a sub shell.

· MASS NO: the sum of no of protons nd neutrons in the nucleus.

· MOLECULAR ORBIT: a polycentric region in space associated with two or more atoms in a molecule.

· NEUTRON: uncharged sub atomic particle having a mass of 1 amu

· NUCLEUS: the central +vely charged core of an atom tht contains practically all the mass.

· ORBITS: another name for the principle energy levels occupied by electrons in atoms.

· ORBITAL: region in space around the nucleus whr the probability of finding an electron is geatest. each orbital can hold a maxi. Of 2 electrons

· ORBITAL QUANTUM NO: same as azimuthal quantum no:

· PAULI EXCLUSION PRINCIPLE: as azimuthal quantum no:

· PARAMAGNETIC: the atom of a paramagnetic substance possesses permanent magnetic moment due to unbalanced electron spin.

· PHOTONS: light quanta (hv)

· PHOTOELECTRIC EFFECT: the phenomenon in which certain metal surfaces such as cesium, sodium,?,emit electrons, when electromagnetic radiations of sufficient energy are allowed to fall on them.

· PRINCIPLE QUANTUM NO: the no: used to designate the principle energy levels tht an electron may occupy I a n atom. it determines the energy level.

· PROBABILITY DISTRIBUTIONS OF ELECTRONS: the probability tht an electron with an atom will be at a certain point in space at a given time; determined by the magnitude of the square of the wave function.

· QUANTIZED: a quantity is said to be quantized, if in accordance with quantum mechanics, it can only have certain discrete values. Such a quantity cannot vary continuously, differences in value separated by jumps.

· QUANTUM: According to the quantum mechanics, energy exists in discrete units, only whole no: of which can exist. Each unit is called a quantum.

· QUANTUM MECHANICS: According to it, energy is quantized,i.e; emitted or absorbed in discrete units, the magnitude of which is given by the product of the frequency nd Planck?s constant.

· QUANTUM NUMBERS: An electron within an atom is specified by set of four numbers, called quantum number.

1) The principle quantum no: (n) defines the shell in which the electron occurs.

2) The azimuthal quantum no: (i) defines the shape of the orbit nd energy sub level.

3) The magnetic orbital quantum no: (m) determines the orientation of the orbit, with reference to a fixed direction

4) The spin quantum no: (s) distinguishes b/w the clockwise nd anticlockwise spin of an electron. this no: is either +/- ½

· RYDBERG?S CONSTANT: A constant relating to those atomic spectra which are similar to the hydrogen atom spectrum. for hydrogen, Rydberg constant is 109.737 cm^-1

· SPECTRAGRAPH: An instrument by which spectra may be photographed.

· SPECTRASCOPE: An instrument for spectrographic analysis or the observation of spectra.

· SPECTRUM: The result obtained when electromagnetic radiations are resolved into their constituent wavelengths or frequencies.

· THRESHOLD FREQUENCY: light incident on a metal will give rise to the emission of electrons only if the frequency of the light is greater than a certain threshold value, which is characteristics of the metal used.

· VOLT: A potential difference which applied across the ends of conductor having resistance of 1 ohm, causes a current of 1 ampere to flow.

· WAVE FUNCTION: in wave mechanics orbital electron is treated as three dimensional stationary wave system represented by a wave function the magnitude of which represents by the variation of amplitude of the wave system at various points around the nucleus.

· WAVE LENGTH: the distance b/w consecutive crests. it is equal to the velocity of the wave motion divided by its frequency.

· WAVE MECHANICS: According to it every particle is considered to be associated with a kind of periodic wave.

· WAVE MOTION: The propagation of a periodic disturbance carrying energy.

· WAVE NO: no of waves in unit length. reciprocal of wavelengths.

· X ? RAYS : Electromagnetic radiations of short wavelength of range 5x10 ^-7 cm to 6x 10^-10cm.

· ZEEMAN EFFECT: When a substance, which emits a line spectrum, is placed in a strong magnetic field, the single lines are split up into group of closely spaced lines

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Jyothi Susan George

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