Why are atomic weights not round?

[domvasta]

Just a clarifying point, the energy is not holding the atoms together, the energy is released when the atom forms, you need to put that much energy back in in order to separate them back into 3 or 4 helium atoms respectively.

[needamuffin]

Carbon-12 weighs *exactly* 12 amu because that's how the unit is defined. 1 amu = 1/12 the mass of a single carbon-12 atom.

[PaulHobbs]

This video has it exactly backwards The bonds don’t represent bounded positive energy (and therefore mass), but negative energy. That’s why the atoms with more bonds have less mass - fusion releases energy when larger atoms are created (up to iron).

[adamkhan]

I always thought those masses represented weighted average masses based on average abundance of different isotopes in any given sample

[DJ_Force]

I think you have it backwards. An atomic nucleus has LESS energy than individual subatomic particals, which is why fusion gives off energy. That lower energy results in a lower mass.

It takes less energy to hold larger atoms together (up to iron), and less energy is less mass.

[cgsrtkzsytriul]

It’s the binding energy of the nucleus. The mass has been converted to energy like in nuclear fusion reaction.

[lilyrooney]

not to be that person but i sure hope this gets referenced during a longer video because shorts aren't the format for everyone and people are going to skip over this because of that.

[greenappleisspicy]

For those who are confused or maybe feel like this explanation is wrong, I will do my best to explain. What is being talked about is something called the "mass defect." You can research that yourself, but as a briefer it is the difference between what we'd predict the mass of an atom to be based on its components, and it's actual mass. Notably, the mass of Carbon-12 (11.178 GeV) is actually *LESS* than the mass of the 6 protons, 6 neutrons, and 6 electrons (11.270 GeV)! This is the case for *all* of the elements, it's a very cool result which is predicted by Quantum Field Theory! In case you needed just one more reason to love physics!

[TheOmegaAlfa]

I’m dating my age with changes on periodic table since I’ve graduated and, damn, I’m ancient. 😂

[NXaiUL]

It's hilarious how confidently wrong people are in the comments. Probably kids who recently learned the basics of the periodic table.

[sp_ce.]

Iron is actually the element with the highest binding energy (and thus lightest compared to its particle count), which makes it the “most stable” element. Fusion provides energy, up to iron, after which fission provided energy and fusion costs energy. This is why stars go supernova when their cores form iron, as fusing it no longer provides outward pressure.

[Artemis_Capsule]

The actual reason is not that mass is converted to energy, because energy has mass, so you wouldn’t lose any mass that way. The reason is because when the protons and neutrons come together they release a little energy, hence losing mass, same thing with bonds being created, O2 weights less than 2O because when the oxygen is bonded, the 2 atoms lose some energy when that bond forms, losing a little energy

[omm-oi]

Accidentally found one of the best educational channel

[GlenMacDonald]

Thank-you for answering a basic question about chemistry that annoyed the hell out of me during high school, and was never discussed. It made the numbers look so ugly and unsatisfying. Knowing where this "error term" comes from would've helped me to not hate the subject -- which I did!

[protyaysamajdar]

Wait, isn't weight calculated based on isotopes and their percentages? Like for chlorine, 3/4 of all chlorine isotope is 35 amu, rest is 37 amu. Thus its weight is 35.5.

[navidahmed]

Your understanding touches on two different but related concepts in chemistry and physics: isotopic abundance and nuclear binding energy. Both explanations you mentioned are correct but pertain to different aspects of atomic mass.

1. **Isotopic Abundance**:
- **Chlorine's Atomic Mass**: The atomic mass of chlorine (35.45 grams per mole) is an average that reflects the relative abundances of its isotopes, chlorine-35 and chlorine-37. Specifically, chlorine-35 has a mass of approximately 34.96885 u and makes up about 75.78% of chlorine found in nature, while chlorine-37 has a mass of approximately 36.96590 u and constitutes about 24.22%. The average atomic mass is calculated based on these proportions.
- **Oxygen's Atomic Mass**: Similarly, the average atomic mass of oxygen (15.999449 grams per mole) accounts for the natural abundances of its isotopes, mainly oxygen-16, oxygen-17, and oxygen-18, with oxygen-16 being the most abundant.

2. **Nuclear Binding Energy**:
- The second argument you mentioned pertains to the concept of nuclear binding energy, which explains why the mass of a nucleus is less than the sum of the masses of its constituent protons and neutrons. This "missing mass" is converted into energy, which is used to hold the nucleus together, according to Einstein's equation \( E = mc^2 \). This effect is known as the mass defect.
- When comparing the masses of different elements, like oxygen and helium, the mass defect plays a significant role. The average mass of oxygen is not exactly four times that of helium because the binding energy per nucleon varies among different elements and isotopes. Generally, the binding energy per nucleon increases up to iron (Fe), making the nuclei more stable and resulting in a greater mass defect for elements lighter than iron.

**Combining the Two Concepts**:
- **Isotopic Abundance** affects the average atomic mass by considering the different isotopes of an element and their relative abundances.
- **Nuclear Binding Energy** explains the overall mass of an atom by accounting for the mass defect caused by the energy required to bind the nucleus together.

Both explanations are grounded in well-established scientific principles. Isotopic abundance is crucial for understanding why the atomic mass of an element like chlorine is not a whole number, while nuclear binding energy explains why the masses of atoms are not simple multiples of each other.

In summary:
- Chlorine's average atomic mass is due to the relative abundances of its isotopes.
- Oxygen's average atomic mass, while also influenced by isotopic abundance, is not simply four times that of helium due to differences in nuclear binding energy, resulting in varying mass defects.

These concepts together provide a comprehensive understanding of atomic masses.

I got this explanation from ChatGPT when taking in consideration what the author of this video is talking about (nuclear binding energy) and what some comments are pointing to (relative abundance of isotopes contributing to the average atomic mass not being a whole number)

[mertatakan]

E=mc² is wrong, the full version is E²=(mc²)²+p²c². For a thing with to momentum, it is correct though.

[omarsaleh]

It's criminal that you chose blue for Proton and red for electron

[JohnJohnson-lkmt]

Is atomic weight the “average weight of the atom”. So the most common isotopes influence the atomic weight the most.

[Nowochienfan]

Thank you!! This finally made it click in my head why you measure mass as 1/12 of carbon 12 and not just 1 = proton or neutron. It’s because protons and nuetrons actually have different masses depending on the atom right?? I feel like my head just cleared :)