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Question Video: Determining Which Element Has the Higher First Ionization Energy Chemistry

Which element in the pair of adjacent elements, Mg and Na has a higher first ionization energy?

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Video Transcript

Which element in the pair of adjacent elements Mg and Na has a higher first ionization energy?

First ionization energy is the amount of energy required to remove the most loosely bound electron completely from an isolated gaseous atom. We need to determine which element, magnesium or sodium, has a higher first ionization energy. Sodium and magnesium are both found in period three of the periodic table. An atom of sodium has 11 protons and 11 electrons. The 11 protons are in the nucleus, two electrons are in the first electron shell, eight electrons are in the second electron shell, and one electron is in the third electron shell. An atom of magnesium has 12 protons and 12 electrons. The 12 protons are found in the nucleus, two electrons are in the first electron shell, eight electrons are in the second electron shell, and two electrons are in the third electron shell.

The third electron shell is the outermost or valence shell in both of these atoms. An electron in the valence shell is the most loosely bound electron. Each of these electrons is electrostatically attracted to the positively charged nucleus. But since a magnesium atom has one more positively charged proton in its nucleus than a sodium atom, its outermost electron will experience a stronger electrostatic attraction to the nucleus. In order to completely remove this electron from the atom, the electrostatic attraction between the electron and the nucleus must be overcome.

Since the electrostatic attraction between the outermost electron and the nucleus is greater in a magnesium atom than a sodium atom, more energy will be required to remove the electron and the first ionization energy will be higher. In general, the first ionization energy tends to increase as we move from left to right across a period on the periodic table. This is because the valence shell of each atom across the period is the same. But the number of protons in the nucleus is increasing, thereby increasing the electrostatic attraction between the outermost electrons and the nucleus.

So in comparing magnesium and sodium, the element which has a higher first ionization energy is magnesium.

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