Section 2

Atomic and Sub Atomic Physics

Basic Definitions:


Those things that pertain to an atom.

Sub Atomic

Those things that pertain to the parts of an atom.


The basic building block of all molecules.


A molecule composed of one type of atom.


A mixture of different elements.

Basic Structures:

Atoms are made of over 200 different sub atomic particles. The electrons, protons and neutrons are composed of many of these sub atomic particles. [ current theory ]

An electron by convention has a negative charge. A proton by convention has a positive charge. The strength of the charge of an electron and proton are equal.

A neutron has no charge.

The charge of an electron or proton is detected as a magnetic field. This magnetic field is the same as the field seen in magnets. When iron atoms align in a bar ( or any other shape ) their electron/proton magnetic fields are easily measured and viewed ( with iron filings ).

Protons and Neutrons are baryons ( made up of three quarks ) in the family of hadrons ( quark based particles ). A proton is composed of 2 up quarks ( +4/3 ) and 1 down quark ( -1/3 ) held together by very small particles called gluons. A neutron is composed of 1 up quark ( +2/3 ) and 2 down quarks ( -2/3 ) held together by gluons. Another hadron is the meson ( made up of one quark and one antiquark ). A quark ( elemental particle ) is a fermion. [ current theory ]

An atom's structure is composed of a nucleus containing one or more protons and zero or more neutrons, with electrons in the space surrounding the nucleus.

Except for the hydrogen atom all atoms are composed of electrons, protons and neutrons.

The behavior of the electron is based on the electron theory.

The electron ( a fermion ) is a charged lepton ( elemental particle ). The neutrino is an uncharged ( neutral ) lepton. Other leptons are muons and tauonics. Electrons are the least massive of the leptons. [ current theory ]

All particles have their counter part which is called it's anti-particle ( having all the same characteristics except the opposite charge ). As an example the electron has a negative charge and it's anti-particle the positron has a positive charge. An antihydrogen atom can be formed with an antiproton and positron. [ current theory ]

In a relatively stable atom there is one electron and one neutron for each proton.

The most abundant form of Hydrogen has only one proton.

A neutron has slightly more mass than a proton.

A proton is about 1,836 times the mass of an electron.


An atom that has a different number of neutrons than protons. The three common isotopes of Hydrogen are:

Hydrogen ( stable, hydrogen-1, protium, light hydrogen ) with no neutrons,
Deuterium ( stable, hydrogen-2, heavy hydrogen ) with one neutron,
Tritium ( hydrogen-3 ) with 2 neutrons ( unstable, radio active, beta decay ).

Atomic Number, Weight, Mass:

Atomic Number

Is the number of protons in the nucleus of an atom.

Atomic Weight (Mass Number)

Is the number of the protons and neutrons in the nucleus of an atom.

Atomic Mass

Is the average of the total mass of the protons and neutrons of all isotopes of an atom measured in units of 1/12 the mass of the carbon-12 atom.

For atoms lighter than iron, the atomic weight is smaller than the total mass of the protons and neutrons.

For atoms heavier than iron, the atomic weight is a little larger than the total mass of the protons and neutrons. What this means is that to hold the nucleus together requires binding energy extracted from the masses of the protons and neutrons, thus reducing the individual masses of the protons and neutrons. This binding energy is the energy released during nuclear fission.

On the modern periodic table the atomic weight is derived by multipling the atomic number by 2 ( except for hydrogen ). The total mass of the protons and neutrons is not shown. So the previous two paragraphs can not be determined by looking at the periodic table.

Electron Distribution:

Electrons fill the space around the nucleus in specific shells composed of orbitals. Shells are labeled K through Q. Each shell has a limit to the number of electrons it can contain which limits the number of orbitals it can have. Orbitals are regions of space at a specific energy level that an electron can have. Most regions can hold up to 2 electrons. Each shell contains electrons of a particular energy level. The higher the shell number the higher the energy level.

atomic shells

Here is a link to images of the various orbitals: Grand Orbital Table.

n, is the principal quantum number (shell)
l, is the orbital quantum number (orbital)
m, is the angular momentum quantum number (direction the orbital is aligned).

To help a little, n = 1 is the K shell, l = 0 is an s orbital, l = 1 is a p orbital and l = 2 is a d orbital. So a description of 4s3 ( n = 4, l = 0 ) would refer to the 3rd electron in the s orbital in the 4th shell. There is a difference between l, a quantum energy level and the orbital shape. These energy levels are computed mathematically and the shapes are drawn according to the theory of quantum physics. [ current theory ]

SubOrbital Shape Descriptions:

The first shell has a s orbital and is designated as 1s. An s orbital can contain up to 2 electrons. The s orbital is a sphere shaped region surrouding the nucleus.

The second shell has a s orbital ( 2s ) and may also have a p orbital ( 2p ). The p orbital can contain up to 6 electrons. The p orbital has three dual pear shaped regions projecting out from the nucleus.

The third shell has a s orbital ( 3s ) and may also have a p orbital ( 3p ) and a d orbital ( 3d ). The d orbital can contain up to 10 electrons. The d orbital has three dual pear shaped regions and a ring shaped region ( which can hold 4 electrons ) surrouding the nucleus.

The forth shell has a s orbital ( 4s ) and may also have a p orbital ( 4p ), a d orbital ( 4d ) and a f orbital ( 4f ). The f orbital can contain up to 14 electrons.

The fifth, sixth and seventh shells have the same structure as the forth shell. At present the largest atoms ( 87 - Francium 223 to 109 - Unnilennium renamed Meitnerium? 266 ) create only the 7s sub shell.

I don't know the structure of atoms; 110 - Ununnilium 272 ( Uun ) 1994, 111 - Unununium 272 ( Uuu ) 1996, 112 Ununbium 277 ( Uub ) 1996, 113 - not made, 114 - Ununquadium ( Uuq ) 1999, 115 - not made, 116 Ununhexium ( Uuh ) 1999, 117 - not made, 118 Ununoctium ( Uno ) 1999. These atoms are made in reaction chambers.

See Tables - Atomic Order 1 to 54, 55 to 109, 1 to 109 and Atomic Shells 1 to 9, 10 to 18, 1 to 18, for my layout of the Periodic Table for the creation and filing of the orbitals.

G ( group ), atoms with the same number of valance electrons in their outer orbitals ( usually the same shell ) that gives the atoms the same chemical properties as seen in the columns on the periodic table. P ( period ) identifies the how the shells are filled with electrons as seen in the rows on the periodic table.

Chemical Properties of Atoms:

For an electron to move from a higher shell to a lower shell requires that an electron convert some of it's kinetic energy ( the energy of motion ) into potential energy ( energy at rest ). The energy conversion creates an energy packet called a photon. The electrons in the outer unfilled sub shells determines the majority of the chemical properties of an atom.

The most stable atoms are the ones that have only s and p orbitals in their outer shell, that are completely filled. On the periodic table, the atoms; Helium, Neon, Argon are inert and don't react chemically.

The atoms; Krypton, Xenon and Radon are generally inert and don't react chemically, but at high temperatures Krypton and Xenon have been shown that they will form compounds with other elements.

Valency Electrons

The electrons in the outer sub shells that react chemically are called valency electrons. The valency electrons may exist in different shells.

The further an electron is from the nucleus the weaker the connection to the protons. This means the valency electrons are weakly held by the atom and are easily stripped off. Removing an electron from an atom gives the atom a positive charge.


Are atoms that have gained ( negative ion or anion ) or lost ( positive ion or cation ) an electron.

Ions are chemically very reactive and are best known as acids and bases ( alkalis ) who's strength ( acidity ) is measured with a pH test.

An atom with almost enough electrons to fill it's outer sub shells will attract or capture nearby electrons.

An atom with just enough protons to create the outer sub shells, with only a few electrons to fill the outer sub shells, will easily give up or be stripped of the valency electrons.

Ionic Binding

Is a connection between atoms because they are ions.

A weakly held electron will be captured by an atom with a few unfilled outer sub shells. The negative charged ion will weakly hold the positive charged ion.

Atoms that have a near balance between the electrons in the outer sub shells and the number of regions not filled with electrons can easily capture an electron or be stripped of an electron. This quality is important in electricity.

Covalent Bonding

Is a connection between atoms by sharing electrons in the outer shell and these connections are called molecular orbitals. The electrons move between the two atoms.


Alpha Particles

Basically the nucleus of a helium atom ( 2 protons and 2 neutrons, an ionized helium atom, no electrons ).

These particles are given off in the decay of an isotope.

Metal foil .003 centimeters thick can stop ( absorb ) this radiation.

Beta particles

Are electrons given off in the decay of an isotope.

Metal foil .3 centimeters thick can stop this radiation.

Gamma Radiation

Is high kinetic energy given off in the decay of an isotope.

Gamma radiation can be produced by other means.

Lead is used to stop this radiation.

What was covered:

Author: David Bishop

Last updated: Nov 16, 2014