Over time, the model of atoms that we have now is becoming less accurate as scientists discover new elements with different number patterns. This is because our current understanding of physics does not take into account these newer discoveries!
The atomic model was first proposed in 1897 by Ernest Rutherford who suggested that all matter is made up of smaller particles called electrons orbiting around a more massive particle called an atom nucleus.
This theory has been very successful in explaining many properties of normal materials such as what makes iron strong or diamonds hard.
But it no longer works for some newly discovered super-heavy elements like element 113 which have over 110 neutrons in them. Because they have so much neutron content, researchers cannot find any electron orbitals that make sense to describe their structure.
The discovery of the electron
In 1897, Scottish physicist Ernest Rutherford conducted an experiment to determine the nature of radioactivity. He put some radium (an element that naturally emits radiation) in a beaker containing heavy water (dihydrogen oxide), placed the mixture under a bright light, and waited!
As the material decayed, it gave off more radioactive rays that can physically bombard other atoms. These encounters create various reactions which result in isotopes (similarly structured molecules made up of different elements).
By studying the ratio of heavier to lighter versions of these isotopes, we are able to determine the structure of the original atom. We know this because as time passes, some atoms lose their electrons and then become neutral particles, so they no longer interact with other matter.
The less prevalent version of these isotopes will have fewer electrons than the more common one, creating an imbalance which can be measured and studied. This is what makes it possible to identify the individual atomic numbers of each element.
With this information, scientists were able to establish the model we use today to describe how atoms work – the atomic model. According to this theory, there is only one kind of particle that exists within every atom — the negatively-charged proton.
This protons attracts positively charged electrons, creating an electrically positive ion. Because ions cannot exist alone without opposite charges, another particle emerges; the positron, or “positive electron”.
The discovery of the neutron
In the beginning, scientists didn’t know what happened when atoms connected with each other. They knew that some elements were made up of smaller particles called ions, but they had no idea how many or what size theseionswere!
In 1897, British physicist Ernest Rutherford conducted an experiment in which he bombarded gold dust with alpha (alpha) radiation. He noticed something strange happen to the gold—it disappeared. This is because the alpha particle was so energetic it smashed into pieces, leaving nothing behind except for energy.
This isn’t possible, though, says the atomic model we have now. Atoms are always left over even after a big explosion, and they never lose any electrons. So where did all the missing gold go?
That’s when Rutherford realized there must be another type of particle involved in this process. He referred to this new particle as the neutron.
Neutrons don’t break down matter like alpha particles do, so the remaining bits of gold radioactively decayed into lead. Scientists eventually determined the ratio of protons to neutrons in different materials using chemical analysis and radioactive decay.
By the late 1920s most physicists agreed that the nucleus contained mostly neutrons, making the atom totally neutral. But none of them could explain why there was a finite amount of positive charge inside the atom.
The classic model of the atom assumed that every electron would immediately jump away from the positively charged nucleus, reducing its total negative charge.
The discovery of the pi-meson
In 1952, physicist Peter Higgs predicted that there must be an additional particle in the nucleus of every atom. This was his “theory of fundamental particles” which predicts that as atoms are broken down into their constituent parts, there should be a particle left over. His theory suggests this new particle is called the higgs boson or sometimes referred to as the Higgs field.
Hence, his prediction for the existence of the higgs boson has since been verified through experiments. It was not until decades later when physicists were able to detect it directly with very sophisticated equipment.
This happened in 2012 at CERN where they used large magnets to isolate and capture the higgs boson.
Since then, many theories have sprung up about what the higgs boson actually is but no one is totally sure! Many people refer to it as the God particle due to its similarity to the famous theoretical concept from religion.
The discovery of the pion
In 1934, scientists discovered what are now known as pi-mesons. These are not particles that people can actually detect directly with an instrument like a detector. Rather, they are changes in matter caused by particle collisions.
When a pi-meson collides with another atom or molecule, it breaks these parts down into new atoms and molecules. This process is very complex but we know that it always leaves behind something called an electron to make space for the newly formed nuclei.
This means that when a pi-meson hits some other material, electrons get left over. We call this effect electrostatic because electricity arises from the interaction between electrons and oppositely charged materials or substances.
You may have seen pictures where high energy neutrons collide with each other and then break apart into more basic elements, leaving nothing else behind. Just like the pi-meson, this happens because of the exchange of force carriers. In this case, those carrier are photons (or gluons).
The discovery of the mu-meson
In 1967, physicists working at CERN conducted an experiment to see if they could detect a particle that was theorized to exist by Russian scientists. This new particle is called the mu- meson, which has one major implication: it shows that matter does not disappear completely when nuclear fusion (the process in which atoms are made) occurs.
As we know, as atomic nuclei fuse together, two or more protons become fused into a single neutron, and therefore there’s no longer any trace left of the original nucleus!
But this theory about the mu-meson says that some leftover material remains, in the form of a very short-lived ghost particle. Because this phantom particle is so fleeting, however, most people never get to directly observe it.
That is, until now! By creating and smashing heavy particles inside of special equipment, researchers have been able to indirectly measure the effect that the mu-meson has on other particles.
The discovery of the magnetic force
Before the atomic model, scientists didn’t understand how magnets worked. They thought that all materials were made from small particles called atoms which weren’t strong enough to account for why some metals are more powerful than others or even why some magnets stay stuck to other things.
But in 1825, French scientist André-Marie Ampère discovered what we now call the magnetic field while experimenting with electricity. He noticed that when he moved a magnet near a current source it would pull away slowly, then suddenly very quickly.
He repeated this experiment over and over again and was able to measure the strength of his magnets more accurately every time. This is because as the magnet pulled away, it left behind an empty space where there wasn’t any electric charge.
This showed him that the magnet lost kinetic energy by moving through the electric field instead of being dragged along by it like you might drag water across land.
This is why physicists still talk about momentum in solid objects and not motion — once something gets going, it keeps going until it loses speed!
Ampère also realized that this effect only occurred within a certain distance of the current source. Beyond that, the magnetic field became weaker and weaker until it disappeared completely.
He referred to this area as the Magnetic Induction Field Limit and later mathematicians calculated its exact size.
The discovery of the strong force
Before we look at how atoms work, let’s take a step back to review the current model for explaining matter. As mentioned earlier, before quantum mechanics there was the classical atom model. This theory suggests that an element is made up of very small particles called electrons which are negatively charged and atomic nuclei which are positively charged.
As elements combine with each other in chemical reactions, positive ions migrate towards negative ones, creating neutral molecules. These neutral molecules can then be absorbed into another substance or evaporated into space.
The strength of this interaction depends on two things: firstly, the number of protons in the nucleus and second, the number of electron pairs in the outer shell. The stronger the pull, the more tightly electrons are bound within the nucleus, and vice versa.
By looking at the effects of different heavy metals on living organisms, researchers have determined that gold is particularly toxic because it mimics calcium by binding to proteins. When protein functions are disrupted, cells cannot function properly and some may even die.
This is why tannin-rich plants like oak galls are used in medicine – they contain high levels of gallium, which has similar properties to gold. By studying the effects of gallium on animals, scientists have been able to determine that it is not toxic.
Since atoms don’t actually exist as individuals, but only as waves of probability, understanding the effect of individual components is important.
The discovery of the weak force
In 1932, British physicist Henry Gwyn Jeffery Beams made an unexpected observation while working with alpha particles at Columbia University. When he directed these particles onto a thin metal plate, some would bounce off, but others would stick to the surface.
He repeated this experiment several times, and noticed that the size of the bouncing particle was different for each test. This showed that there is another type of fundamental particle in addition to the electron we know about.
This new particle was later named the “neutron” due to its neutral charge. Because it has no net electrical charge like electrons do, it does not interact with other matter or light atoms via electrostatic forces (the main reason why we know about electrons).
Instead, the neutron interacts only very slightly with heavier atomic nuclei through what is now known as the strong nuclear force. This explains how neutrons are so common — they’re just too heavy for the strong force to hold onto!
The strong force isn’t the only way that subatomic particles interact, though; there’s also the weaker electromagnetic force and the much stronger gravitational force.
