ATOMIC STRUCTURE

ELEMENTARY PARTICLES

COMPOSITE PARTICLES

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FERMIONS

Can be an elementary particle or a composite particle.

Particles with half-integer spin are fermions.

LEPTONS

A lepton is an elementary, half-integer spin (spin 1/2) particle that does not undergo strong interactions.

Each lepton has one anti-particle.
There are six leptons. The neutral leptons are called neutrinos.

BOSONS

Examples of bosons include fundamental particles such as photons, gluons, and W and Z bosons, the Higgs boson, and the graviton of quantum gravity; and some composite particles like helium-4

QUARKS

SIX FLAVORS

FUNDAMENTAL INTERACTIONS

+2/3 CHARGE

-1/3 CHARGE

HADRON

PROTONS

PROTONS are Baryons

Two UP quarks
One DOWN quark

Symbol: n, n0, N
Neutral charge (0)
1.675 x 10^-27 kg
1.009 amu

Neutron number determine ISOTOPE

In 1886 Eugene Goldstein discovered positive rays through a gas discharge experiment.

Symbol: p or p+
positive 1 charge
1.673 x 10^-27 kg
1.0073 amu
Equal to Atomic Number

NEUTRONS

NEUTRONS are baryons

One UP quark
Two DOWN quarks

Symbol: n, n0, N
Neutral charge (0)
1.675 x 10^-27 kg
1.009 amu

Neutron number determine ISOTOPE

BINDING ENERGY

Protons and neutrons are termed as nucleons and responsible for the mass of atom.

Protons and neutrons are packed together in a very small space in the nucleus.


There must be some force of attraction between these particles to maintain the existence of nucleus.

The columbic force of attraction is not enough to hold many particles in such a small space, as the repulsion force between protons would render the nucleus highly unstable and tend to disintegration.
Hence, the force of attraction between nucleons which is stronger than the repulsive force between protons is called NUCLEAR FORCES.

Nuclear binding energy = Δmc2

protons 2 x 1.00728
neutrons 2 x 1.00866 mass of parts = 4.03188 amu

alpha particle mass
4.00153 amu
4.03188 vs 4.00153

The stability of any nucleus is depends on the ratio of number of neutron and proton present in atom.

Those nucleus with n/p ratio of ONE are highly stable.
Elements with high n/p ratio are unstable and radioactive in nature. Elements up to atomic number 20 are stable with n/p =1, as atomic number increases, n/p ratio increases and instability increases.

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ELECTRONS

Symbol: e-,
Negative 1 charge
9.109 x 10^-31 kg
0.0005486 amu (1/1836)

Classified as fermions

Pauli Exclusion Principle

Both particles and waves

Antiparticle called POSITRON

ELECTRON SHELL

• Principle Quantum number (n)
• 2n^2
• First shell accommodates 2 electrons
• Second shell 8 electrons
• Third 18 e-

ELECTRON SUBSHELLS

• 10 electrons in d orbital
• 14 electrons in f orbital

MAGNETIC QUANTUM NUMBER

• (m)
• Any integer between -L and +L

SPIN QUANTUM NUMBER

• Spin clockwise (+1/2)
• Or spin counterclockwise(-1/2)

PAULI EXCLUSION PRINCIPLE

• NO two electrons in the same atom can
• have the same 4 quantum numbers

AUFBAU PRINCIPLE

• Electrons added to an atom,
• One at a time,
• Starting with LOWEST energy orbital

HUND'S RULE

• One electron is added to each orbital
• before two electrons are added to any orbital together
• Electrons are added with the same value of spin until
• each orbital in the subshell has at least one electron

EXCEPTIONS

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