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"A chemical bond may be defined as the attractive force which holds together the constituent atoms of a chemical species." Cause of chemical combination 1. Tendency to acquire noble gas configuration : Octet rule.The first logical explanation about the cause of chemical combination is based upon the study of electronic configuration of noble gases. The electronic configuration of these elements is given in table. Fore the study of electronic configuration  of these gases it is revealed that the s and p orbitals of the outermost shells are completely filled.(In case of helium,there is only one orbital i.e.,1s which is completely filled).The unusual stability of noble gases was linked with the s2p6 configuration (1s2 in case of helium) of the noble gases. The electronic configuration of all the remaining elements do not have 8 electrons or s2p6 configuration all these elements are chemically reactive.The principal of acquiring 8 electrons in the valence shell is called...

A force which acts for a very short time but produces an appreciable change of momentum is called impulsive force . Impulse is defined as the total change in momentum produced by the impulsive force.                                                       or Impulse is defined as the measure of large force on a body for a very small duration.In some cases the force acting on a body is not constant or it acts for a very short time.For example,when a collision takes place between two bodies or when a blow is made.With a hammer,it is ordinarily not possible to measure the actual value of the force as its value changes with time.In such cases the effect of the force is measured by the total change in momentum that it produces in a given time. If the velocity of a body of mass m change from u to v in t second,then the total change in momentum during this...

Momentum : The quantity of motion possessed by a moving body is called momentum.It is measured by the product of mass and velocity of the body.It is a matter of common experience that a car moving slowly can be stopped more easily than when it is moving fast.Similarly,a cricket ball hit moving gently can be caught easily but it is difficult to catch it if is moving fast.These examples show that greater the velocity of a body,the greater is the force required to stop it. Again a cricket ball and a tennis ball may be moving with the same velocity but a greater force is required to stop the cricket ball than that required to stop the tennis ball.This shows that greater the mass of the body,greater is the force required to stop it. From the above,we conclude that the force required to stop a moving body or conversely to move a body with a given velocity depends upon two factors (i) velocity and  (ii) mass of the body.This product of the mass and the velocity of a moving body is kn...

If a number of force are acting on a body at the same point then these forces are called concurrent and if these forces are unable to change state of the body i.e.,body remains in its state or rest or of uniform motion along a straight line,then the body is in the state of equilibrium and so are these forces. Thus,the number of forces acting on a body may be in the state of equilibrium if these forces produce zero resultant force. Let us consider three concurrent forces F 1 (vector),F 2 (vector) and F 3 (vector) acting simultaneously at the same point O. Let force F 1 (vector)and F 2 (vector) be represented by two sides of parallelogram,complete the parallelogram.Find the resultant of these two forces F 1 (vector)and F 2 (vector),this will act along OC' i.e.,along the diagonal of the parallelogram.                             →  →     →  Therefore        ...

Force may be defined as a pull or push which produces or tends to produce,stops or tends to stop the motion of a body.e.g., (i) To move a football,we have to exert a push i.e.,kick on the football. (ii) To stop football or a body moving with same velocity,we have to apply push in a direction opposite to the direction of the body. (iii) A man is trying to move a wall but fails to displace it. (iv) To change the direction of motion of moving body along a straight line we have to apply a sideways push or pull on it. Thus,the push or pull which changes or tends to change the state of rest or uniform motion of a body along a straight line is called force. Force is vector quantity. Units of force (i) S.I.System:S.I.unit of force is newton or kg ms -2 . (ii) C.G.S.System: C.G.S unit of force is dyne or g cm s -2 . (iii) Gravitational unit: Gravitational unit of force is kgf.                      1N = 10 5  dyne ...

(i) To measure small distances,we use the following units: (a) 1 millimetre i.e.,1 mm = 10 -3  m = 10 -1 cm. (b) 1 micron = 10 -6  m (c) 1 angstrom = 10 -10 m (d) 1 fermi = 10 -15 m (e) 1nanometre = 10 -9  m (f) 1 barn = 10 -28 m  2      [ used for measuring nuclear cross-section] (ii) To measure very large distance we use the following units: (a) 1 astronomical units (AU): It is defined as the mean distance of earth from sun.                              1 AU = 1.496*10 11  m ≅ 1.5*10 11  m. (b) Light year : It is the distance travelled by light in one year. If velocity of light is 3*10 8 m/s in vacuum and one year is equal is 365 day *24 hr * 60 min * 60s.                      distance = velocity * time Therefore      1 light year = 3* 10 8 *365 *24*60*60 = 9.46*10 5  m ...