All substances are made of Atoms; even though they are unable to be seen by not only the human eye but through any sort of microscope, we know that they are there. Atoms have a radius on average of about 〖1×10〗^(-10) m (micrometres). In this paper I will be talking about:
The History of The Atom.
Atoms, what are they made of?
Atoms are built up of 3 sub-atomic particles: Protons, Neutrons and Electrons. Protons and Neutrons are contained within the Nucleus of an atom. The nucleus is in the centre of the atom and has a radius of around 〖1 x 10〗^(-14) m (that is roughly 1/10 000 of the atoms overall radius). 99.9% of an atoms mass is concentrated in its nucleus.
Electrons move around the nucleus in shells. This makes up the rest of the atom. Electrons are negatively charged unlike Protons that are positively charged. Even though they are incredibly small they cover a lot of space within an atom. The volume size of an electrons orbit contains the overall size of the atom itself. Electron have a mass of virtually nothing.
Particle Relative Mass Charge
Proton 1 +1
Electron 1 -1
Neutron 0 Very Small
(This Table Shows the Relative Mass and charge of all three sub-atomic particles.)
There is the same number of Protons in an atom as there are Electrons. Therefore, atoms have no overall charge. Protons have positive charges and Neutrons have negative charge. These charges are opposite and consequently cancel out. However, in an ion the number of Protons is different to the number of Electrons. This creates an overall of charge of either Positive or Negative. E.g. An ion with a charge of 3- has three more electrons than it has protons.
On the Periodic Table of Elements each element has its own Nuclear Symbol, Atomic Number and Mass Number. Both the Atomic and Mass Numbers relate to the specific elements atomic properties. The Atomic Number (also known as the proton number) tells you the number of protons there are. The Atomic Number can also tell you the number of electrons that are in that atom (This is because atoms have the same number of Protons as it does Electrons). The Mass Number tells you the number of Protons and Neutrons added together. For Example:
The Element Sodium (Na) has an atomic number of 11. This means it has 11 Protons and 11 Neutrons. Sodium also has a Mass number of 23. This means Sodium that there are a total of 23 proton and neutrons. To find the number of Neutrons without the protons added to it we take away the Mass Number from the Atomic Number.
23 – 11 = 12. Therefore, there are 12 Neutrons in Sodium.
The History of The Atom.
The theory of the atom has been going since the early 19th Century. The first theory of atoms came from John Dalton. Dalton described atoms as Solid Spheres, he also stated that the different spheres made up the different elements. In 1897 JJ Thompson concluded from Daltons experiments that atoms were not in fact solid Spheres. Thompson`s measurements of charge and mass showed that atoms must contain smaller negatively charged particles with in it. These negatively charged sub-atomic particles were called Electrons. This new theory was known around the world as the `Plum Pudding Model`.
Further on in 1909 Ernest Rutherford and his student Marsden conducted a series of experiments called “Alpha particle scattering experiments.” They fired alpha particles on a very thin sheet of pure gold.
Due to the “Plum Pudding Model” Rutherford and Marsden were expecting the particles to pass straight through the gold sheet or be slightly deflected. This hypothesis was made because the positive charge of each atom was thought to be very spaced out through the “Pudding” of the atom. However even though most of the particles went straight through like predicted, more particles were deflected that expected. Therefore the “Plum Pudding Model” could not be right.
Rutherford came up with a new way to explain and share his new evidence. He did this through “The Nuclear Model.” This version of the Nuclear Model is like the Plum Pudding Model however this model shows that the protons are concentrated inside of a nucleus.
Scientists soon realised that electrons in “Clouds” around the Nucleus of an atom, as described by Rutherford, would be attracted to the Nucleus. This would cause the atom to collapse. Neil’s Bohr`s Nuclear Model of the atom suggested that all the electrons were contained in shells. Bohr suggested that electrons orbit the nucleus (Like the moon orbiting Earth) and were not anywhere between the atom and its shells. Each shell had a fixed distance away from the nucleus. This version of “The Nuclear Model” is the model known globally today.
Thank You for Reading.
By Harry Dodd-Sutton
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