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Jyothi

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Important Chemical Terms - 1

Atomic Structure

A

ALPHA PARTICLE: A sub atomic particle tht has a mass of 4 unit?s nd a charge of +2. i.e.; a doubly charged helium ion (H²⁺)

2)

ANTIBONDING MOLECULAR ORBITAL: a molecular orbital formed by the subtraction of wave functions of the combining atomic orbitals.it destabilizes the molecule.

3)

ATOMIC MASS UNIT: unit used for expressing the masses of individual isotopes of elements, approximately equal to 1.66x 10^-24g

4)

ATOMIC NUMBER: the no of protons in the nucleus of an atom or no of electrons rotating around the nucleus of the neutrals atom

5)

ATOMIC MASS: the mass of an atom expressed in amu units.

6)

ATOMIC ORBITAL: region in space around the nucleus of a n atom, whr the probability of finding an electron is greatest. Each orbital can hold a maxi of 2 electrons.

7)

ATOMIC SPECTRUM: a group of characteristic pattern of lines in which each line represents a specific wave length of radiation, emitted by the atoms of an element.

8)

AUFBAU PRINCIPLE: electrons enter the various orbital to their respective capacities in increasing order of energy.

9)

AZIMUTHAL QUANTUM NO: denotes the sub shell tht an electron occupies nd specifies the shape of the electron cloud.

BALMER SERIES: Wave length ( ) of the series is given by:

1/

= R_N[1/2^{2_-1/n2_{],whr n}}₂>2

BETA PARTICLE: identical to electron in all respects

BOHR?S THEORY: according to Bohr?s theory:

1) The electrons in an atom are located in orbits or energy levels, around the nucleus.

2) The electrons in orbits closest to the nucleus are of lower energy than in orbits further away frm the nucleus.

3) Every electron in an atom may hav only certain allowed energies. This energy determines wht orbit the electron occupies.

4) The angular momentum of an allowed orbit of an atom is integral multiple of h/2

i.e.; m

r=nh/2

5) Electrons can move frm one orbit to another. To do this, an electron must gain or lose a certain exact amount of energy-a quantum of energy. Thus:

E₂-E_{1 =}E=h

BOHR?S THEORY OF HYDROGEN ATOM: wavelength of a spectral line in hydrogen atom is given by:

1/

= R_h[1/n_{1^{2 - 1/n2}}²]

14) BOND ENERGY: energy characterizing a chem. bond b/w two atoms, measured by the energy required to separate the two atoms.

BONDING MOLECULAR ORBITAL: an orbital formed as a result of addition of wave functions of atomic orbitals. It stabilizes the molecules.

16)

BOND LENGTH: the distance of the strength of the bond b/w the two atoms. Defined mathematically as

Bond Order= [no: of electrons in bonding molecular orbitals] - [no of electrons in antibonding molecular orbitals] / 2

17) COULOMB: a unit of electricity equal to ampere times second

18)

DE-BROGLIE CONCEPT: A wave can be a particle nd a particle can be a wave

19)

DE-BROGLIE REACTION: the wavelength (

) of a mass(m) moving with a velocity(v)is given by:

***

= h/m

20)

DUAL NATURE OF RADIATION: light has particle like nature nd each particle possesses wave characteristics also.

21)

ELECTROMAGNETIC RADIATION: a form of energy transmitted thrgh space without the apparent transmission of matter.

22)

ELECTRON: a subatomic particle having a charge -1 nd a mass of approximately 1/1840 of amu

23)

ELECTRON CLOUD: an orbital, the region in space around the nucleus, whr the probability of finding an electron is greatest.

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ELECTRON DIFFRACTION: the diffraction effect resulting frm the passage of electrons thrgh matter. This phenomenon provides evidence for the existence of wave associated with electrons.

25)

EMISSION SPECTRUM: the displayed wavelength distribution of light, coming frm an emitting substance.

26)

EXCITED STATE: an energy level of greater energy then the ground level

27)

EXTRA NUCLEAR PART: consists of electrons revolving around the nucleus in orbits.

28)

FREQUENCY: the no of vibrations per sec.

29)

GROUND STATE: the most stable energy state of an electron. i.e; the state in which electrons are in the lowest energy level available to them.

30)

HEISENBERG?S UNCERTAINTY PRINCIPLE: It is impossible to determine with accuracy both the position nd the momentum of a particle simultaneously. Thus:

***

x.m

> or =h

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Jyothi Susan George

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