what’s the actual difference between different atoms besides just some protons, neutrons and electrions?



What is it about, let’s say arsenic atoms, that makes it so much more deadly than gold for example. And please expand this to molecules too.

In: Chemistry

Interestingly enough, nothing. In most cases it’s all about how the electrons exist around the nucleolus. Different numbers of electors create different “shapes” to the atom.

What happens is that the electrons attract to the protons but repel from each other. Because of this every different number of electrons create a different atomic shape. I recommend looking up some pictures online.

These shapes of electron clouds allow atoms to share and borrow elections. These exchanges create chemical bonds, and pretty much define our world.


With most things, it is how reactive they are, or if their presence disrupts other processes in the body.

Put sodium chloride (table salt) in water, no reaction. Put sodium in water, it violently explodes. Sodium is very reactive. Its valence electron wants to react to something (other metals in the same row on the periodic table can do the same thing, like Potassium.

Chlorine is the same way. Chlorine wants to react. It can asphyxiate us very easily. It combines with sodium to make something mostly harmless.

It’s always about the dose. Water can kill humans if we drink too much of it.

Most of the effects you are talking about are just the chemistry of the atoms. The chemistry is a result of how many electrons they have and “want,” which is a result of the number of protons they have. So the difference between arsenic and gold, in the end, is that arsenic has 33 protons and gold has 79. That changes how they work chemically, and how a body will process them (it’ll just excrete the gold, but the arsenic will be bioactive in nasty ways). If you had an arsenic atom and could add 46 protons to it, it’d be gold. This is what we mean by a “chemical element,” so if it seems tautological, it sort of is — gold is any atom with 79 protons, arsenic is any atom with 33.

The number of neutrons influences the physical properties of the atom — notably it can determine whether it is radioactive or not, and how radioactive it is. So any atom with 79 protons is gold, but depending on the number of neutrons it might be normal gold, or it might be radioactive gold. These different types of atoms, with different neutron counts, are called “isotopes.”

Lastly, molecules are just groups of atoms that are joined together by shared electrons. Again, how this works is going to be determined by the chemistry, which means by the electrons, and so ultimately the protons.

>What’s the actual difference between different atoms besides just some protons, neutrons and electrons?

Well only one – electron configuration.

Electrons arrange themselves in shells or orbits around the nucleus. As the atomic number increases, one by one electrons keep adding to a shell. Once a shell is full, new electrons start filling up a new shell. If you are in 11th grade, you should know that the first shell can accommodate 2. the 2nd can accommodate 8, the 3rd shell can accommodate 18 electrons and so on..

Here’s where we reach the concept of ‘valency’ or ‘valence electrons’. Generally, for an atom to be most stable, it needs a fully filled outer shell. An atom will do anything in it’s power to achieve a fully filled outer shell.

Let’s take 2 examples – An alkali metal Sodium (Na) and a Halogen Chlorine (Cl). Alkali metals are the atoms which have 1 electron in their outermost shell and halogens are those atoms who are just one electron short of filling their outermost shell. Now when given an opportunity to lose that extra electron, Sodium will VERY readily do so so that the outermost 1 electron is gone and the 2nd last shell now becomes it’s outermost shell and the Sodium ion is now very stable. That’s why alkali metals are very reactive and we are advised to not touch them bare-skinned, unlike copper or iron or gold.

Similarly halogens just need 1 atom to fill their outermost shell completely and achieve atomic ‘Nirvana’. So they readily react with anything they can pull an electron from. And that’s why Flourine, Chlorine are dangerous gases which we are told not to inhale.

Now what about an atom that already has a fully filled outermost shell? Well they are extremely non-reactive and are called ‘inert’ gases for that very reason. Argon, Neon, Xenon, etc are used to fill up cavities where the inner materials are susceptible to reactions. Hence many bulbs come filled with inert cases and we have ‘neon lights’ because the Neon wont react with the metal filament inside (or any other part for that matter).

**TLDR: The farther away you are from achieving an outermost filled shell, the less reactive the atom is going to be.. generally. Ofcourse it’s not that simple because once you start to delve into it, you learn about orbitals and hybridisation and what not which makes the matter more complex, but I hope you get the gist of it – it’s all about how the electrons are arranged in the atom.**

Everything about their properties truly emerges from the protons, neutrons, and electrons. That’s really just it. However, I can point out how that’s the case, which may illuminate things for you a little.

The amount of protons dictates the amount of electrons in a neutral atom. A hunk of plain carbon is going to have 6 protons and 6 electrons. So why is carbon black, solid at room temperature, why does it bond to itself in complicated chains, etc? Well, it has to do with largely with energy and electric fields. The protons create an electric field that the electrons interact with. This determines “where” the electrons can be around the atom and how much energy is binding them in their “spots”. The quotation marks are because electrons are quantum mechanical, so saying they’re in a particular place is kinda tricky.

So if you have a whole bunch of plain carbon in a clump, the protons and electrons determine the electric field around the atom, which affects how the individual atoms behave near each other. The electric attraction from these fields is relatively strong, which is why carbon is solid at room temperature. It sticks it all together into a chunk. Those fields are also why it’s black: the electric fields in the carbon resonate with light waves in such a way that they can absorb the energy from the light, making it opaque and black looking.

If we bond some other atoms onto our carbons to make something like propane, the electrons and protons are arranged in a new way. They have different electric fields, so they are attracted to each other and other molecules in a different way. Since they propane molecules are weakly attracted to each other, propane is a gas at room temperature. The molecules also hold a higher potential energy than plain carbon, which means we can set propane on fire to release that energy and get back carbon (and water and CO2).

So why is arsenic more dangerous than gold? Because the way it interacts with the molecules in your body (through the electric force mainly) is different than gold. It tends to bond to particular molecules in your body in a way that screws up how those molecules function, causing the machinery of your body to break down.

Follow up question. What makes something solid vs liquid? Can you have molecules that are solid that have identical molecular structure but one is solid and one is liquid? In this case, what further detail is needed to account for the differentiation?

Is your question, “what’s the difference between different types of atoms/molecules”, or “what makes certain atoms/molecules more dangerous than other atoms/molecules”? I’ll answer the former and then the latter.

Atoms are lego bricks; they vary in size and shape because of the shape and amount of plastic used to create it (in this metaphor, subatomic particles are collectively the plastic). Molecules are then all the different ways you can arrange your lego bricks. Certainly you can imagine that some individual lego bricks *have the potential* to cause more harm than others (eg that one tiny brick that’s a bit broken so it always falls off and gets stepped on), and certain lego-built items are more dangerous than others (something with rounded edges VS a lego sword or something).

In either case, it’s not the atom/molecule/lego brick/lego house that is dangerous on its own, it’s the *effect it has on other things* that makes it dangerous.

Now imagine you have two lego-built items: a firmly packed ball and a giant messy cluster with sharp pieces all over the place and pieces falling off everywhere.

Also imagine that all living things are created out of legos as well.

Imagine that you, a giant lego person, are tasked with eating one of your two lego items. You must choose between the compact ball or the cluster of sharp, loose bricks.

You, an intellectual, realizing you are made of lego bricks, realize that if you eat the loose cluster, a brick may get loose and get lost somewhere in your body. Even worse, it may *stick to one of your inner-body legos*, causing who knows what damage. Even WORSE, it may stick to one of your inner legos, and *stick so strongly that when your body goes to dislodge it, a bunch of your own inner legos are dislodged with it*. So you opt for the compact ball, and it passes though you without displacing any of your inner legos. Phew!

Now imagine you are given the same choice again, but instead of you eating it, it is your dear pet Blorb. Blorb is a strange creature who is also made of of legos, but he’s kind of a cluster of legos himself. His insides are all basically loose legos, and his lego systems are specially arranged to deal with small loose particles floating around. But while his body handles loose clusters well, larger solid objects tend to shove all of his inner legos around, messing up the arrangement and making him very sick. So for Blorb, you elect to have him eat the loose cluster, and he lives. Phew!

This is a very ELI5 version of why certain chemicals are dangerous to certain things. All legos have the ability to affect other legos, and certain lego arrangements can be especially suited to handle certain shapes while other shapes may destroy everything.

Same with atoms and molecules, and everything built up from that. Drinking water is necessary for survival, but injecting a bunch of water directly into your veins can cause your blood cells to absorb the water and explode, killing you. Eating chocolate is great but feeding chocolate to a dog will make them very sick. It all boils down to your inside legos reacting to outside legos in ways that cause harm.

Hopefully this is ELI5 enough but still a reasonably accurate metaphor. Also I’m not a chemist so all corrections are welcome!

The moment you start asking about “why is X deadly”, the answer necessarily stops being about the physical properties of X itself (the number of protons and neutrons, electron configuration, etc.) and more about “what thing in the body does it fuck with that really, *really* needs to be working properly to keep me not dead”.

Typically it involves bricking a specific protein, and often it does that by accidentally getting attached to a very important part of the protein – the part where an actual reaction is supposed to be taking place – and not letting go. Rendering it as useless in sort of the same way as if you put Flex Glue instead of motor oil in your car’s engine.

In the example of arsenic, it bricks a protein called pyruvate dehydrogenase by sticking to the sulfur atoms in it. Pyruvate dehydrogenase is very important for the process of the cell producing energy. Without it working properly, the whole cell sort of grounds to a halt and shuts down because it runs out of energy to do anything.

Gold doesn’t do this. Gold doesn’t really want to stick to any important proteins in your body.