Transcription of Chapter Twelve ATOMS
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Chapter Twelve ATOMS
INTRODUCTIONBy the nineteenth century, enough evidence had accumulated in favour ofatomic hypothesis of matter. In 1897, the experiments on electric dischargethrough gases carried out by the English physicist J. J. Thomson (1856 1940) revealed that ATOMS of different elements contain negatively chargedconstituents (electrons) that are identical for all ATOMS . However, ATOMS on awhole are electrically neutral. Therefore, an atom must also contain somepositive charge to neutralise the negative charge of the electrons. But whatis the arrangement of the positive charge and the electrons inside the atom?In other words, what is the structure of an atom?The first model of atom was proposed by J. J. Thomson in to this model, the positive charge of the atom is uniformlydistributed throughout the volume of the atom and the negatively chargedelectrons are embedded in it like seeds in a watermelon.
12.1 The magnitude of this force is 2 0 1 (2 )( ) 4 eZe F r (12.1) where r is the distance between the α-particle and the nucleus. The force is directed along the line joining the α-particle and the nucleus. The magnitude and direction of the force on an α-particle continuously changes as it approaches the nucleus and recedes away from it.
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