How is it possible that helium, having 2 protons, and lithium, having 3 protons, are so different in terms of their physical properties? How come one is a gas at room temperature and the other is a solid metal?

Then why lithium and beryllium, the latter having 1 proton more than the former, are both metals and solids at room temperature?

Now if you remove neutrons from the nuclei of any element (except hydrogen), they form isotopes that have similar chemical properties and different physical properties, while still being an atom of the same element - therefore the protons, if I understand it correctly, are what determine whether an element is a gas or a solid at room temperature, and not the neutrons (or even electrons). Is this true?

The deeper question is that why do the properties of elements and their atoms change significantly - in some cases as with helium and lithium - just by having an additional proton in their nucleus, if the fundamental building blocks of protons (quarks) are identical for each proton? Then in the case of lithium and beryllium, why is the change in physical properties so subtle compared to the first case?


This question has already been asked before, however I am specifically interested in helium and lithium - why is one a gas and the other a solid metal at room temperature, having completely different chemical and physical properties? Is this a result of the electron shell configuration? Why does an extra proton, neutron and electron give rise to such a difference?

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    $\begingroup$ It is the electron shell structure that determines the physical properties of elements. The number of protons happens to be the same as the number of electrons (atoms are neutral), so your questionis about atomic rather than nuclear physics. $\endgroup$ Jul 28, 2019 at 14:02
  • $\begingroup$ Thank you for your suggestion, I have changed the question tag. But why then the lithium ion Li+, having 2 electrons, is still very different from the atom of helium, also having two electrons? The only difference being the number of protons in this case. $\endgroup$
    – mawej1
    Jul 28, 2019 at 14:14
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    $\begingroup$ Because $Li^+$ has total charge $+1$, and $He$ has total charge $0$. This makes a big difference in their chemical and physical behavior. $\endgroup$ Jul 28, 2019 at 14:25
  • $\begingroup$ The noble gases are generally the seemingly most special cases when compared to anything else on the periodic table. The most similar properties are found along the vertical axis on the table. Other than that it depends on what you mean by similar. $\endgroup$
    – user234190
    Jul 28, 2019 at 14:36
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    $\begingroup$ Exact duplicate of What enables protons to give new properties to an atom every time one is added? $\endgroup$ Jul 28, 2019 at 14:42

2 Answers 2


He is a noble gas. It has a completely filled 1s shell. Li has one electron more that resides in the 2sp shell. Be has 2 electrons in this shell. Both atoms therefore have an unfilled valence shell, are analogous for example Na and Mg, also both metals.


Scientists discovered that exist elements which are not reacting with other elements (expectations see below) nor with themself and call these gases noble elements. Furthermore it was found out that these elements have electron configurations with 2 (He), 8 (Ne), 8 (Ar), 18 (Kr), ... electrons in the outmost shell around the nucleus. It was stated that the noble elements all are gases.

From the emission and absorption spectra of excited elements and based on the outdated now notation that electrons revolve around the nucleus, a formula for electron orbitals was proposed, which does not matches the above mentioned number of electrons. Physics some rules and exception formulations are needed to explain, what chemists sorted into the Mendelejew table (see the history of the periodic table).

The noble elements all are gases and they not react or react only under special conditions (for example XeF6). The reason is easy to understand if one realize that spin respectively the magnetic dipole moment of the involved electrons play the leading part in the relations on the atomic level. Two and eight electrons around the nucleus suffice themselves. The interaction with other atoms is reduced to minimum. The do not react nor do they form chains or other structures. They simply gases because the have no interatomic bonds.

Occupying space around the nucleus with two electrons, nature doesn’t allow more electrons in this orbital and two electrons in the next orbital (Be! not Li as you suggested) are not leading again to a complete shell. One may explain this by the distance of the outer electrons from each over. However, four pairs of electrons form the next complete shell and so do the next 8 electrons again. With less or mor electrons as the noble configurations these electrons form intermolecular and other bonds with neighbor atoms.

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    $\begingroup$ "spin respectively the magnetic dipole moment of the involved electrons play the leading part in the relations on the atomic level" -- this is utterly incorrect. Please stop posting misinformation. There is no excuse for not reading up on the basics; this book offers a good introduction. $\endgroup$ Jul 29, 2019 at 18:04
  • $\begingroup$ @EmilioPisanty My question Has anyone tried to incorporate the electrons magnetic dipole moment into the atomic orbital theory? did not clarify your comment. Could you explain more in detail? $\endgroup$ Jul 30, 2019 at 17:51
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    $\begingroup$ This answer claims that interactions between electrons' magnetic dipole moments play a "leading part" in atomic structure (above, say, electrostatic interactions between the nucleus and the electrons and among the electrons, and spin-orbit coupling for the electrons). This is utterly incorrect. Copious amounts of detail can be found in any atomic physics textbook (which we've been pointing you to for many years now, and which you have no excuse for not reading). $\endgroup$ Jul 30, 2019 at 18:20
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    $\begingroup$ Getting up to speed is your responsibility, and claiming lack of knowledge as an excuse for posting misinformation is not appropriate. What parts of this are unclear? $\endgroup$ Jul 30, 2019 at 18:20

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