Fundamental Forces and Atoms

History of the Atom

There have been many different ideas of the atom and the answer to the fundamental question "what is stuff made of?" even going back to ancient times.

Democritus and Leucippus came up with the theory that eventually if you cut things in half enough times, you will reach something that is not divisible. This was known as "atomos," meaning indivisible.

Aristotle didn’t believe in the theory of the atom; instead thought all things were made up of earth, fire, air, and water in differing amounts.

Elements were a common concept throughout many ancient people, each with their own way of breaking down the fundamental idea of what stuff is.

Greece, China, and India all had their own versions of the elements!

Alchemy was around for a long time combining these theories, pseudosciences, more philosophy, and the scientific method. Eventually a lot of parts of alchemy transformed into modern chemistry, first by Antoine Lavoisier in the late 1700s (who systematically renamed and identified things through experiments with gasses) and later by John Dalton, who combined things from many places of the past and shaped all of atomic theory.

JJ Thomson discovered the electron, making a model that he thought looked like plum pudding.

Ernest Rutherford discovered the nucleus. Due to this he is credited with the discovery of the proton, the particles in atoms with a positive charge.

Robert Millikan determined that electrons have a specific electric charge and helped find that atoms were actually able to be divided further into particles.

Neils Bohr proposed the idea of fixed electron orbits in the early 1900s, creating a model that we still use to show a lot of information about the element's electrons.

Erwin Shrodinger mathematically proved the existence of electron clouds, with electrons staying in orbitals, locations for these fixed orbits around the nucleus.

James Chadwick discovered the neutron using radiation, the particle in the atom with a neutral charge.

Murray Gell-Mann proposed the theory of quarks. Quarks are the things that make up the particles, letting us look at how radiation and atomic particles interact.

Modern Atomic Theory

In our modern day understanding there are two regions of the atom:

The nucleus, containing protons and neutrons. This nucleus contains almost all the mass and is really tiny compared to the atoms actual size.
- The number of protons determines what element an atom is and this information is placed in the central circle of the model. They have a positive charge.
- The number of neutrons brings stability to the atom and is also placed in the central circle. They have no charge.
The electron cloud, containing the electrons. This electron cloud contains most of the space of an atom. Electrons within the electron cloud are negatively charged and are usually found within fixed orbitals that are located within it. These fill up in rings around the atom (2 for the first ring, 8 for the second, 8 for the third, 18 for the fourth, 18 for the fifth, and 32 for any beyond that) and have negative charges. The reason they form these rings will be discussed later on in the unit.

When atoms have the same number of protons and a different number of neutrons, they are known as an isotope. Protons determine the element formed while protons and neutrons added together determine the mass. For example:

An atom with 1 Proton and 0 Neutrons would be Hydrogen-1
An atom with 1 Proton and 1 Neutron would be Hydrogen-2
An atom with 2 Protons and 2 Neutrons would be Helium-4
An atom with 6 Protons and 6 Neutrons would be Carbon-12
An atom with 6 Protons and 8 Neutrons would be Carbon-14
An atom with 26 Protons and 29 Neutrons would be Iron-55

We can represent atoms through atomic symbols and numbers. When using atomic symbols the capital letters denote a new element and elements can have either 1 or 2 letters associated with their symbol. The list of all different elements can be found on the periodic table.

There are many relationships between these numbers and symbols:

The element's name and symbol are based on their atomic # and you can find it on the Periodic Table
Atomic # is the same as # of protons
Atomic # (and protons) is the same as # of electrons with no charge
Mass # = protons + neutrons
Neutrons = Mass # - protons
Charge = protons - electrons
Electrons = protons - charge

Fundamental Forces

Whenever any particle or object interacts with another, it does so through the use of the four fundamental forces of nature. The four fundamental forces are as follows:

Gravity: Gravity is based on mass and pulls objects together. Of all the forces it's the weakest, usually needing a large mass to create enough force to matter. It has infinite range.
Electromagnetic Forces: Electromagnetic forces include most things with a charge of some sort, including electricity, polarity, magnetism, and even light waves. It has infinite range and is stronger than both gravitational forces and the weak nuclear force.
Strong Nuclear Force: The strongest fundamental force that is used to hold atoms, their nuclei, and their particles together. It has a short range.
Weak Nuclear Force: A weak force used for some nuclear processes that transform a particle into a different particle. It has a short range.

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