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Which element has more metallic character - aluminium or magnesium?

I know that metallic character decreases along a period (from left to right) and increases down a group.

Aluminium comes after Magnesium in the same period (period 3) in the periodic table. So, I thought Magnesium would have greater metallic character.

However, I read in a book that Aluminium has greater metallic character. Is this true? If this is true, why?

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    $\begingroup$ +1 Nice question, it depends on how do you define the metallic character... $\endgroup$
    – G M
    Commented Jan 10, 2017 at 14:23

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Two types of metallic character

In fact, there are two type of metallic character if you look at the metal from the chemical point of view or if you look at the metal from the physical point of view:

So it really depends on how do you define metallic character

Chemical metallic character

Since metallic character in chemistry is defined as:

the tendency of an atom to lose electrons.

We can understand that it is directly related to electronegativity.

chemical property that describes the tendency of an atom to attract electrons (or electron density) towards itself

Basically, it is the opposite (that would be Electropositivity...)! An so it increases from right to left. The picture below shows the electronegativity but can be used for the purpose.

enter image description here

I think the reasoning that the book wants you to do is not remembering all the subshell but just the basic chemistry principles. So from the chemical point of view $\ce{Mg}$ has a greater metallic character compared to $\ce{Al}$.

Physical metallic character

The physical metallic character is defined taking in account the physical properties of the metal. A metal, from the physical point of view, has a high electrical conductivity, high thermal conductivity, and high density.

These properties are harder to predict: enter image description here In this case, however, $\ce{Al}$ has a more metallic character compared to $\ce{Mg}$.

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Yes, you are right that $\ce{Al}$ is more metallic than $\ce{Mg}$.

It is because, $\ce{Mg}$ have fully filled $3\text{s}$ subshell. Due to this, the first ionisation energy$^{[1]}$ of $\ce{Al}$ (578 kJ/mol) is less than that of $\ce{Mg}$ (738 kJ/mol).

Filled and half-filled subshells show a small increase in stability in the same way that filled shells show increased stability. So, when trying to remove an electron from one of these filled or half-filled subshells, a slightly higher ionization energy is found.$^{[2]}$

You can also say that higher levels of subshells are further away from the nucleus which is why it is easier to remove an electron from $\ce{Al}$ than from $\ce{Mg}$.

References:
1. http://en.wikipedia.org/wiki/Ionization_energy
2. http://www.grandinetti.org/ionization-energy-trends

Edit: Updated reference(s)

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    $\begingroup$ Well I'd quibble a bit about ionization energies being the defining characteristic of metallic character. I think electrical resistivity would be more characteristic. A metal isn't much of a metal in a gas. Ni has a lower ionization potential than copper in a gaseous state (737.1 vs 745.5) but a higher resistivity (69.3 vs 16.78). $\endgroup$
    – MaxW
    Commented Nov 5, 2015 at 2:58
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    $\begingroup$ I don't think that using Yahoo Answers as reference add value to your assertion... eheeh... $\endgroup$
    – G M
    Commented Jan 10, 2017 at 14:28
  • $\begingroup$ @GM : edited! And now Stack Exchange wants me to write 2 more characters in this comment so I wrote a lot more than just 2. :p $\endgroup$
    – ashu
    Commented Jan 11, 2017 at 16:13
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Mg is more metallic than Al due to its tendency to lose electrons. As a result, the electropositivity decreases as we go across periods. Electropositivity is related to metalic character and vice versa. As a result, Mg has a greater electropositivity then Al as well as being more metallic.

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    $\begingroup$ The metallic character is given by free electrons in the solid metal. Aluminium has, after silver, copper and gold, the fourth highest electrical and thermal conductivity of all metals. Therefore aluminium is considered more metallic than magnesium. $\endgroup$
    – aventurin
    Commented Apr 3, 2016 at 18:56
  • $\begingroup$ @aventurin it depends if you look at the metal from the chemical or the physical point of view $\endgroup$
    – G M
    Commented Jan 10, 2017 at 14:26
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Ionization is inversely proportional to metallic character, III-A and VI-A Show abnormalities in ionization energy and Al is in III-A and its ionization energy is less than Mg that's it is more metallic than Mg.

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As metals can easily remove an electron .Aluminium is more metallic than magnesium because the last electron in Mg enters in s orbital and in Al it enters in p orbital and s orbital is more penetrating towards nucleus so it is difficult to remove an electron in Mg.

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