The entire field of chemistry is derived from attraction and repulsion. You have learned that like charges repel, while opposite charges attract. Most likely, you were introduced to this concept in comparison to a magnetic dipole. This is an easy comparison to grasp early on in your chemistry journey since it is something that is observable in nature; most of us have spent time playing with magnets, watching in awe as opposite poles attract while like poles repel. However, electromagnetism is really more complicated than that.
But what, then, does it mean for a particle to be charged? What physical process accounts for electric charges? And most importantly, how do we define an electric charge?
To understand this concept, we must consider electromagnetism as it really is – it is a force, just as gravity is a force. Just as gravity causes objects to fall toward a central point, usually a massive object, a charged particle has an invisible “electric field” around it that causes it and other charged particles around it to experience a force, either attraction or repulsion, based on their charges.
It was first theorized in 1935 that forces were carried by “messenger particles” – in other words, that each fundamental force was, in fact, facilitated by the exchange of a distinct subatomic particle.
Later, it was found that four fundamental forces existed from which all other forces could be derived. Three of these forces are outlined by the Standard Model of Particle Physics: Electromagnetism, the Strong Nuclear Force, and the Weak Nuclear Force. The final force is Gravity, which physicists are still not sure how to incorporate into the Standard Model.
Electromagnetism is based on attraction and repulsion between particles, some being “negatively” charged, and others being “positively” charged. Every charged particle has an electric field around it that causes particles with the same charge, when brought in contact with it, to repel and particles with the opposite charge to attract.
The “carrier particle” for electromagnetism is the photon. It is theorized that in the case of all the four forces, the way 2 objects interact is based on particles emitted by one that are absorbed by the other. The absorption of the particle transfers momentum from one object to the other.
The Strong Nuclear Force is a force that has an extremely short range but is responsible for binding the nucleus together. Before the 1970s, physicists were puzzled why superheavy nuclei should not simply fly apart. In essence, the Strong Force is an attractive force between quarks, subatomic particles that make up protons and neutrons. The force is believed to be mediated by two classes of particles: mesons and gluons.
The Weak Nuclear force is responsible for nuclear fission and relates to the “spin” of subatomic particles. It is facilitated through the exchange of particles called bosons. The final fundamental force is Gravitation, or gravity. Gravity has an infinite range and is responsible for holding together all objects in the universe that have mass. Physicists are still unsure how to account for the effects of gravity on a subatomic level, and are working to develop a quantum theory of gravity that explains the effect of Einstein’s theory of relativity with respect to the motion of subatomic particles. Scientists have proposed several possible components of this theory, the most notable being that massless particles called gravitons are responsible for the gravitational force.