Atomic and nuclear structure

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Alpha-particle scattering experiment

*https://www.youtube.com/watch?v=dNp-vP17asI&t=4s

https://www.youtube.com/watch?v=1EdTw4I6L0U

Alpha particle aka helium nucleus

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Interpretation of observation

Observation 1: Most particles passed through undeflected or with small deflection.

Deduction 1: The atom consist of mostly empty space.

Observation 2: Small fraction (<1%) of α-particles are deflected through large angles.

Deduction 2: All the positive charges in the atom are concentrated as a nucleus in a small region of space as compared to the diameter of the atom. [only possible if atom consists of a +ve charged nucleus of very small dimensions]

Observation 3: Few particles are reflected backwards, through an angle close to 180°. [when close to nucelus, due to large repulsive force]

Deduction 3: The nucleus is very massive. [in terms of mass] [small in terms of volume]

atom consist of mostly empty space

positive charges in the atom are concentrated in a small region of space (nucleus - the red circle)

The electrons revolve around the nucleus in allowed orbits

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Nuclide Notation

Isotopes same no. of protons (same no. of electrons hence same chemical properties) but different no. of neutrons.

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Nuclear Reactions

Reaction between 2 nucleus

NOT A CHEMICAL REACTION

Conservation of NUCLEON NUMBER [1+235 = 141 +92 +3(1)]

Conservation of CHARGE [0 +92 = 56 +36 + 0]

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Mass defect

Individual nucleons are heavier than nucleus

mass defect is the difference between mass of nucleons and mass of nucleus

Mass Energy Relation

Mass can be converted to energy and vice versa BUT

Mass may not be conserved

Energy may not be conserved

HOWEVER:

Total mass-energy MUST BE CONSERVED

Binding Energy

Minimum amount of energy to separate nucleus completely into its constituent nucleons

BE = (mass defect)c^2 [ in JOULES]

Energies in nuclear physics usually expressed in eV

To convert to eV -> divide by 1.6 x 10^-19 so For Mev divide by 1.6 x 10^-13

higher BE = more stable

Less stable DOES NOT MEAN unstable; still stable just not as stable

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Tutorial