Thomson And Rutherford's Model Of Atom Flashcards
Postulates
Every atom consists of a positively charge sphere
The way seeds are embedded in watermelon….. Electrons are also embedded in positively charged sphere
Positive charge and mass is uniformly distributed
Although this model could explain electrical neutrality, or was discarded after Rutherford’s model
Conclusions of Alpha ray experiment
Since most of Alpha particles passed straight without any deflection, most of the space inside atom is empty
Since Alpha particles are positively charged, they can be deflected by positively charged body inside atom
Since very few Alpha particles are deflected by 180, positively charged body must be occupying small volume
Since Alpha particles are heavy, they can be deflected by a heavy body only. Therefore positively charged body must be heavy
Relation between number of Alpha particle and scattering angle
N(θ) ∝ 1/sin⁴ (θ/2)
Relation between impact parameter and scattering angle
B ∝ 1/θ
Value of impact parameter when θ = 180
b = 0
Relation between scattering angle and atomic number
θ ∝ z
Postulates (1)
Every atom consists of a positively charged nucleus around which electron revolves in circular path called orbits….. This motion is composed with motion of planets around the Sun
model is also known as Rutherford’s Planetary Model of atom
Postulates (2)
entire postive charge and mass of atom is concentrated at one point called nucleus
opposite point Of Thomson Model
Postulates (3)
The electrostatic force between nucleus and electron is balanced by centrifugal force
Postulates (4)
Radius of atom is of order 10-¹⁰m
Radius of nucleus is of order 10-¹⁵m
Distance of closest approach
Rmin = 2ze²K/ KE or 2ze²K/ 1/2mv²
Radius of nucleus
Rn = Ro × A⅓
Ro = 1.2 × 10-¹⁵m
A = mass number
