Important Chemical Terms - 1
Atomic Structure
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+)
ANTIBONDING MOLECULAR ORBITAL: a molecular orbital formed by the subtraction of wave functions of the combining atomic orbitals.it destabilizes the molecule.
ATOMIC MASS UNIT: unit used for expressing the masses of individual isotopes of elements, approximately equal to 1.66x 10-24g
ATOMIC NUMBER: the no of protons in the nucleus of an atom or no of electrons rotating around the nucleus of the neutrals atom
ATOMIC MASS: the mass of an atom expressed in amu units.
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.
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.
AUFBAU PRINCIPLE: electrons enter the various orbital to their respective capacities in increasing order of energy.
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/
= RN[1/22-1/n2],whr n2>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 -E1 =
E= h
BOHR?S THEORY OF HYDROGEN ATOM: wavelength of a spectral line in hydrogen atom is given by:
1/
= Rh[1/n12 - 1/n22]
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.
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
COULOMB: a unit of electricity equal to ampere times second
DE-BROGLIE CONCEPT: A wave can be a particle nd a particle can be a wave
DE-BROGLIE REACTION: the wavelength () of a mass(m) moving with a velocity(v)is given by: *** = h/m
DUAL NATURE OF RADIATION: light has particle like nature nd each particle possesses wave characteristics also.
ELECTROMAGNETIC RADIATION: a form of energy transmitted thrgh space without the apparent transmission of matter.
ELECTRON: a subatomic particle having a charge -1 nd a mass of approximately 1/1840 of amu
ELECTRON CLOUD: an orbital, the region in space around the nucleus, whr the
probability of finding an electron is greatest.
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.
EMISSION SPECTRUM: the displayed wavelength distribution of light, coming frm an emitting substance.
EXCITED STATE: an energy level of greater energy then the ground level
EXTRA NUCLEAR PART: consists of electrons revolving around the nucleus in orbits.
FREQUENCY: the no of vibrations per sec.
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.
HEISENBERG?S UNCERTAINTY PRINCIPLE: It is impossible to determine with accuracy both the position nd the momentum of a particle simultaneously. Thus:
· HUND?S RULE: when several orbital of the same type are available, the electrons 1st 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
| | ![[Post New]](file:///C:/DOCUME%7E1/KKSYST%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image002.gif) posted on 17 Apr 2007 22:39:48 IST |
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| Let's take Figure 1 to be a pictoral representation of our problem: a boat on the floor, with a rope pulling it. First we will represent the boat -- the 'body' in our problem -- as a (really) simplified figure, a square (Figure 2). |
Figure 2 Simplified diagram of the ship |
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Gravity
The first force we will investigate is that due to gravity, and we'll call it the gravitational force. We know that the acceleration due to gravity (if on Earth) is approximately g = 9.8 m/s . The force, by Newton's Second Law is F = m g where g is the acceleration due to gravity. Let's add this to our diagram (Figure 3). Note that the force vector, labelled Fmg, points downward, as this is the direction in which the gravitation force acts. Note that this force is commonly called weight. This 'weight' (m g) is different from our everyday use of the word 'weight' (which is known in physics as 'mass'). |
Figure 3 Ship, with the gravitational force labelled |
Normal | The normal force one which prevents objects from 'falling' into whatever it is they are sitting upon. It is always perpendicular to the surface with which an object is in contact. For example, if there is a crate on the floor, then we say that the crate experiences a normal force by the floor; and because of this force, the crate does not fall into the floor. The normal force on the crate points upward, perpendicular to the floor. It is called the normal force because normal and perpendicular mean the same thing. The normal force is always perpendicular to the surface with which a body is in constact. For a body on a sloped surface (say a ramp), the normal force acting on that body is still perpendicular to the slope. In the case of our problem, the ship, we will pretend the ship is being pulled | . on a floor. (This is because on water there is the complication with another force, buoyancy. For simplicity's sake, we will ignore buoancy by putting the ship on the floor.) Let's add the normal force to our FBD (Figure 4), andrepresent the normal force with the script 'N',  . |
| Related to the normal force is the frictional force. The two are related because they are both due to the surface in contact with the body. Whereas the normal force was perpendicular to the surface, the frictional force is parallel. Furthermore, friction opposes motion, and so its vector always points away from the direction of movement. Friction is divided into two categories, static and kinetic. These are represented by the script 'F', with a subscript 's' for static friction: , and a subscript 'k' for kinetic friction,  . As its name suggests, static friction occurs when the body is not moving (i.e. "static"). It is the force which makes it difficult to start something moving. On the other hand, kinetic friction occurs when the body is in motion. This is the force which causes objects to slow down and eventually stop. Friction is usually approximated as being proportional to the normal force. The proportionality constant is called the coefficient of (static or kinetic) friction. The constant is represented as  for static friction, and  for kinetic friction; it depends on the actual surface with which the body is in contact. To summarize, We've added (kinetic) friction to our free body diagram, Figure 5. | 
Figure 5 Ship, with gravitational, normal, and frictional forces |
Push and Pull
| Another force which may act on an object could be any physical push or pull. This could be caused by a person pushing a crate on the floor, a child pulling on a wagon, or in the case of our example, the wind pushing on the ship. We will label the push force caused by the wind with Fpush | 
Figure 6 Ship, with gravitational, normal, frictional, and push forces |
Tension
| Tension in an object results if pulling force act on its ends, such as in a rope used to pull a boulder. If no forces are acting on the rope, say, except at its ends, and the rope itself is in equilibrium, then the tension is the same throughout the rope. We will use the letter T to represent tension in a free body diagram. If we say that our ship is being pulled by a rope at its front end, then we can add this force to our FBD (Figure 7). |
Figure 7 Ship with gravitational, normal, frictional, push, and tension forces
|
And there we have it: all the forces acting on our ship has been labelled in Figure 7. This is the complete FBD for our problem of a ship being pulled along a floor by a rope.
Moderation Team
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