# Nuclear Structure Protons and Neutrons

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```					Rutherford Experiment’s to probe the Structure of Atoms Using Alpha Particles

Th90 4 Ra88 + a(He2++) nuclear reaction

It was time to study the structure of the atom!
Ernest Rutherford proposed the following Experiment

Fig. 1-12, p. 23
He Atomic Structure: Nucleus(positive charge) + Electrons(negative charge)

Snap Shot
at an instant time
oversized nucleus

-

2+
He Atomic Structure: Nucleus(positive charge) + Electrons(negative charge)

Electrical Force
Snap Shot
Coulomb’s Potential
at an instant time
V(r)=q1q2/4πe0 r
oversized nucleus
q1=+2e
q2=-e
e0-permittivity                             r
of vacuum             -

2+
Nuclear Structure: Nucleus(Protons and Neutrons). He

Snap Shot
at an instant
time ,
oversized nucleus
-
Nucleon(proton/neutron) Structure: Quarks ===============Physics

Snap Shot
at an instant
time ,
oversized nucleus
He: ======= Chemistry======

Snap Shot
at an instant
time ,
oversized nucleus
-

2+
Summary: Electrons, Protons and Neutrons.

The basic building blocks of matter are the Elementary Particles: Protons(p), Neutron(n) and
electrons(e)
mp= mn = 1836 me= 1.67 x 10-27 kg
Atomic Mass ~ Nuclear Mass!
Average atomic mass unit(amu) = 1/16 the 16O (8 neutrons and 8 protons)
The mass of 16 O is smaller than the mass of 16 mp?

The atomic mass scale is then chosen such that 1.0 grams= N0 amu
N0= 6.022 x1023 is Avogadro’s number; represents a “mole” of particles, atoms/molecules
Electron charge qe = -e and protons qp= +e 1.6 x10-19 C(coulombs)
Neutrons have Zero charge qn = 0
Protons and Neutrons make up the Nucleus
radius ~ 10 x 10-15 m or 10 fm (femto-meters, Table B.3)
Held together by nuclear forces with very large Binding Energies >106 eV
(eV= electron volt, energy of an electron when accelerated across a 1 Volt potential)
1eV = 1.6 10-19 J
(Joule = Nm, a Newton-Meter)
Energy required to move 1.0 meter(m) against 1.0 Newton(N) Force
Summary: Electrons, Protons and Neutrons.

The basic building blocks of matter are the Elementary Particles: Protons(p), Neutron(n) and
electrons(e)
mp= mn = 1836 me= 1.67 x 10-27 kg
Atomic Mass ~ Nuclear Mass!
Average atomic mass unit(amu) = 1/16 the 16O (8 neutrons and 8 protons)
The mass of O16 is smaller than the mass of 16 mp E=DmC2 the nuclear binding energy
Dm=mass difference due to the conversion of mass to nuclear binding energy
The atomic mass scale is then chosen such that 1.0 grams= N0 amu
N0= 6.022 x1023 is Avogadro’s number; represents a “mole” of particles, atoms/molecules
On this scale the mass of a 1.0 moles of H atoms: mH=1.008 grams, mH2O=18.016 gram
Electron charge qe = -e and protons qp= +e 1.6 x10-19 C(coulombs)
Neutrons have Zero charge qn = 0
Protons and Neutrons make up the Nucleus
radius ~ 10 x 10-15 m or 10 fm (femto-meters, Table B.3)
p and n are held together by nuclear forces with very large Binding Energies > 106 eV
(eV= electron volt, energy of an electron when accelerated across a 1 Volt potential)
1eV = 1.6 10-19 J
(Joule = Nm, a Newton-Meter)
Energy required to move 1.0 meter(m) against 1.0 Newton(N) Force
Periodic Table and the Classical Concept of Energy
Neutral Atoms(Z electrons): H, He, Li, Be, B, C, N, F, etc
Held together by Electrical Forces (binding energies ~1-1000 eV also call
ionization energies) between electrons and the Z protons in the atomic
Nucleus via the
Coulomb Potential V(r) = q1q2/4πe0r
Z = number of protons= atomic number
N = number of neutrons
A = Z + N= Atomic Mass Number ~ mass of the atom ~ Nmp
Atoms with the same Z and different N are called isotopes
For example Z=1 and N=0 for 1H: Hydrogen
and Z=1 and N=1 for D= 2H: the Hydrogen isotope Deuterium
For Carbon there are several Isotopes    12C:   Z=6, N=6; 13C: Z=6, N=7 and 14C ?
Periodic Table and the Classical Concept of Energy
molecules: H2, O2, H2O, NH3, CO2, CH4, etc and Elemental Solids and Liquids: Au(s),
Si(s), Hg(l), etc are constructed from atoms. By organizing the neutral atoms in terms
of Z, and therefore, the number of electrons we observed periodic behavior in the
properties of atoms, e.g., ionization energy and reactivity. This is the origin of the so
called Periodic Table
Coulomb Potential and the Classical Concept of Energy

For H , the simplest atom, Z=1 and               V(r)
one electron ions,                                      0
He+, Li2+, Z=2 and 3, respectively.                         r
The Coulomb Potential Curve V( r)
binding the electron and proton is written as:
V(r) = (-e)(Ze) / 4π e0 r

e0 = 8.854 x 10-12 C2J-1m-1 Permittivity of Vacuum

r distance between the Nucleus and electron

r            • -e
+Ze •
Coulomb Potential, Force and the Classical Concept of Energy

The Classical Force between can be derived from V(r),
The potential. Classical means non-quantum mechanical

F = - dV/dr =

Decreasing potential, the force is repulsive
Increasing potential, the force is attractive

Total Energy E= KE + PE

Where PE =V(r) is the potential energy curve

Fig. 3-CO, p. 54
Coulomb Potential, Force and the Classical Concept of Energy

The Classical Force between can be derived from V(r),
The potential. Classical means non-quantum mechanical

F = - dV/dr =(-e)(Ze) / 4π e0 r2 in Newtons

Decreasing potential, the force is repulsive
Increasing potential, the force is attractive

Total Energy E= KE + PE

Where PE =V(r) is the potential energy curve

Fig. 3-CO, p. 54
Repulsive and Attractive Coulomb Potential Energy Curves with different charges

Fig. 3-2, p. 61

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