Question

What bonding types affect the melting and boiling points of Alkaline Earth Metals?

Answer 1

Metallic bonds.

Explanation:

Refer to the structure of metals. Metals consist of lattices of metal cations and an ocean of delocalized valence electrons that are not attached any particular nuclei in the network. [1]

Similar to the other two types of chemical bonds: ionic bonds and covalent bonds, the bonds holding up components of metals are electrostatic interactions between opposite charges- the attraction between electrons and metal cations. The melting and boiling points depend on the strength of the bonds, which in terms is directly related to the product of the charges and inversely related to the separation.

(consider the Columb's law for calculating the strength of electrostatic interactions:
`F_Q=k*(q_1 * q_2)/r^2`
where `r` is the distance between the two charges and `k` a constant specific to the substance separating the charges.)

Given the gradual decrease in first ionization energy, one might expect the melting point of alkaline-earth metals (group `2`) to increase down the group; however, this doesn't appear to be the case for all group two elements since as the number of filled valence shell increases, the increase in separation between the cations and neighboring valence electrons overwhelms the charge of the cation. As a result, the strength of the bonds and therefore the melting and boiling points decrease as the principal quantum number (the number of occupied shells) increases.

References:
[1]Libretexts. “Metallic Bonding.” Chemistry LibreTexts, Libretexts, 22 Feb. 2018, chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Chemical_Bonding/Fundamentals_of_Chemical_Bonding/Metallic_Bonding

[2]Haynes, WM, (ed). 2012. CRC Handbook of chemistry and physics. (93rd edition). Boca Raton, US. CRC Press.