The number of electrons should be equal to the atomic number. We can work this out by looking at the atomic number of each element. We can predict the general trend in boiling points down Group 18 by looking at the number of electrons atoms of each element have. While the relationship is quite complex, the general rule is that dispersion forces are stronger when the atoms have more electrons. This is why dispersion forces are sometimes known as instantaneous dipole-induced dipole interactions. This causes the electrons in neighbouring atoms to shift as well, causing small dipole-dipole interactions. Because there are no sources of polarity or ionic behaviour, the only forces that exist between atoms of Group 18 elements is dispersion forces.ĭispersion forces arise from very small fluctuations in the positions of electrons in the atom, leading to one side being slightly negative and one side slightly positive. So, the boiling points of the elements in Group 18 are generally quite low. This means that in a liquid state it doesn’t take a great deal of energy to break these weak interatomic forces. Being monatomic means there are very weak forces between the atoms. This extremely low reactivity means that in their gas state all the Group 18 elements are monatomic. Although, as you descend the group, some of the elements do start to pair up with oxygen and fluorine under extreme conditions. This means in their standard states all Group 18 elements are very unreactive. The same is true for neon, where its 10 electrons fill the first and second electron shells. Being in the first group, these two electrons fully fill the first electron shell. The key feature of elements in Group 18 is that they have full valence shells.įor instance, helium has two electrons. For the other elements, the key feature we need to understand is the forces holding the atoms together. So, for the purpose of this question, it will be ignored. Since oganesson is actually a synthetic element only made in tiny amounts, its boiling point has not been measured. And the standard state of an element is its expected chemical state at one bar of pressure. A boiling point is the temperature at which a substance transitions from a liquid to a gas. The names of the elements in Group 18 as we descend are helium, neon, argon, krypton, xenon, radon, and oganesson. Group 18 of the periodic table can be found to the far right. On descending Group 18 of the periodic table, what happens to the boiling points of the elements in their standard states?
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