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Modern Physics

Atomic Structure
An element is the simplest form of the atom that cannot be broken down into other atoms by a chemical reaction.


The atom is made up of subatomic particles called:

– Electrons

– Protons

– Neutrons

The following table illustrates the properties of these particles:

ParticleElectronic ChargeSize
Electron-11/2000
Proton+11
Neutron01



The atom is structured with protons and neutrons in the nucleus and the electrons orbiting the nucleus.

The essential difference between one atom and another which distinguishes between the elements is the number of protons. Each element has a specific number of protons.The periodic table is a list of all the atoms arranged in ascending order of the number of protons.


To distinguish between the number of different elements the following notation is used:

Mass Number A

Element’s Symbol X

Atomic Numberr Z

Example Chlorine:

The atomic number is the number of protons.


The mass number is the number of protons plus the number of neutrons.


Therefore the number of neutrons is:

Number of neutrons = mass number – atomic number

The number of neutrons is: 37 – 17 = 20 neutrons.

Isotopes

Example Hydrogen

All three atoms are hydrogen except that they are of different mass due to the absence or presence of extra neutrons.


Hydrogen is 99% of all the hydrogen. Deuterium is less than 1% of hydrogen and tritium is a small fraction of the remaining hydrogen.

Nuclear Reactions Theory


Nuclear Fusion
This is the nuclear process when two atoms come together, fuse, and form another element.The most common example of this is when two hydrogen atoms fuse together to form helium in the core of the Sun. The reaction results in a slight decrease in mass and a release of tremendous amount of energy. This mass is released as energy and is the power source of the Sun. These reactions only occur at tremendous temperatures. The internal temperature of the Sun is estimated to be 14 million °C.

Deuterium + Deuterium ——-> Helium

Deuterium has 1 proton, 1 neutron and 1 electron

Helium has 2 protons, 2 neutron and 2 electrons

Nuclear Fission
This is the nuclear process when a large atom breaks up into smaller pieces, which are usually smaller atoms. A common type of reaction is that of a nuclear explosion. In this nuclear reaction a uranium atom is hit by a fast moving neutron. The uranium atom then breaks up into smaller atoms of barium, krypton, plus 3 neutrons. This reaction also releases a large amount of energy.

Nuclear Fusion and Nuclear Fission
The principle of nuclear conservation states that the atomic number and mass numbers (z) are conserved. This means the number of nuclear particles on the right hand side of the equation must equal the number of particle on the left hand side of the equation.
In the reaction of hydrogen fusing with hydrogen the number of electrons, protons and neutrons equals the number of electrons, protons and neutrons in the helium. In total there are:

• 2 protons, 2 electrons and 2 neutrons on the left hand side of the equation, and;

• 2 protons, 2 electrons and 2 neutrons on the right hand side of the equation.

This is the principle of nuclear conservation.