Question

Explain why the first ionization energy of \(\mathrm{Mg}\) is greater that of \(\mathrm{Na},\) whereas the second ionization of Na is greater than that of Mg.

Short answer

The first ionization energy of Mg is greater than that of Na because Mg has a greater effective nuclear charge, holding its electrons more tightly. The second ionization energy of Na is greater than that of Mg because removing a second electron from Na disrupts a stable noble gas configuration, making it harder to remove.

Step-by-step solution

Consider the electron configuration for Na and Mg

Sodium (Na) has an electronic configuration of 1s2 2s2 2p6 3s1 while Magnesium (Mg) has an electronic configuration of 1s2 2s2 2p6 3s2. This means that the outermost electron of Na is in the third shell and the outermost electron of Mg is also in the third shell.

Understand the First Ionization Energy

First ionization energy refers to the energy required to remove the first electron from an atom. For Mg, it's harder to remove the first electron compared to Na because Mg has a greater effective nuclear charge than Na. Mg has 2 electrons in the outermost shell and has stronger attraction to nucleus and more energy is needed to remove one of them.

Understand the Second Ionization Energy

The second ionization energy refers to the energy required to remove a second electron from an atom. For Na, after the first electron is removed, the remaining configuration is the same as neon (Ne), a noble gas, and it is energetically unfavorable to remove an electron from a stable, complete electron shell configuration. Therefore, it takes much more energy to remove the second electron from Na compared to Mg.

Summarize the Results

To summarize, the first ionization energy of Mg is greater than that of Na because Mg has a greater effective nuclear charge. The second ionization energy of Na is greater than that of Mg because removing a second electron from Na disrupts a stable noble gas configuration. This is why Mg has a higher first ionization energy than Na, and why Na has a higher second ionization energy than Mg.

Key concepts

Electron Configuration

Electron configuration describes how electrons are distributed in an atom. Each electron occupies specific energy levels, known as shells, around the nucleus. For Sodium (Na), the electron configuration is written as 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^1\), while Magnesium (Mg) follows 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\). Both Na and Mg have their valence electrons in the third shell. However, Mg has two electrons in the 3s subshell compared to one in Na. This plays a crucial role when it comes to their ionization energies.
Understanding electron configuration helps in predicting how atoms will interact and what types of bonds they might form. It's like knowing which seats are filled in an electron 'bus'- the position can determine the reactivity of the atom.

Effective Nuclear Charge

The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It is a key factor in understanding ionization energy. The outermost electrons do not feel the full charge of the nucleus as they are shielded by inner electrons. Mg, with an electron configuration of 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\), has a higher effective nuclear charge for its outer electrons than Na, whose configuration is 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^1\).
This means electrons in Mg are more tightly held and require more energy to remove. The effective nuclear charge influences the atom's chemical properties, particularly how strongly it holds onto its electrons.- A greater effective nuclear charge results in a higher first ionization energy because electrons are more attracted to the nucleus.

Noble Gas Configuration

A noble gas configuration refers to an atom's state that has completely filled electron shells, similar to the noble gases, which are stable and inert. After losing one electron, Na adopts the electron configuration of Neon (Ne), which is a stable, noble gas configuration. This makes the removal of the second electron much more difficult because it disrupts this stability.
- Noble gases are known for their low reactivity, due to their stable electron configurations. This stability is what makes the second ionization energy of Na higher than that of Mg. - Atoms tend to resist changes that would lead to a less stable, non-noble gas electron configuration.

Periodic Trends

Periodic trends include variations in an element's properties across different periods and groups on the periodic table. One key trend is ionization energy, which generally increases across a period from left to right. This occurs because effective nuclear charge increases, drawing electrons closer to the nucleus and making them harder to remove.
For Na and Mg, this trend is evident as you move from Na to Mg across the period. The first ionization energy of Mg is higher than that of Na due to Mg's increased effective nuclear charge. However, trends can reverse for second ionization energies, as seen with Na, because the noble gas configuration increases the energy needed to remove an additional electron. - Understanding periodic trends helps predict not only ionization energies but also atomic radii, electronegativity, and other critical chemical behaviors.