Problem 107 - Introductory Chemistry Atoms First

Question

Magnesium has a higher first ionization energy than sodium, consistent with the periodic trend for first ionization energies. Postulate a reason why Mg has the higher first ionization energy.

Step-by-Step Solution

Answer

Magnesium has a higher first ionization energy compared to sodium due to its position in the periodic table and its electronic configuration. As magnesium is to the right of sodium in the same period, it experiences a higher effective nuclear charge, holding its electrons more tightly. Consequently, more energy is needed to remove the first electron from magnesium than for sodium.

Step 1: Understand Ionization Energy

Ionization energy is the amount of energy required to remove an electron from a neutral atom in its gaseous state. The first ionization energy refers to the energy needed to remove the first (outermost) electron.

Step 2: Analyze the Electronic Configurations of Sodium and Magnesium

Sodium (Na): Atomic number = 11, Electronic configuration = 1s² 2s² 2p⁶ 3s¹ Magnesium (Mg): Atomic number = 12, Electronic configuration = 1s² 2s² 2p⁶ 3s²

Step 3: Understand the Periodic Trend for Ionization Energy

As we move from left to right across a period in the periodic table, the ionization energy generally increases. This is because of an increasing effective nuclear charge, which results from increasing protons in the nucleus attracting the electrons more strongly. As a result, more energy is required to remove electrons from atoms with greater effective nuclear charges.

Step 4: Compare Sodium and Magnesium

Since magnesium is to the right of sodium in the same period (Period 3), magnesium should experience a higher effective nuclear charge. This means that it should have a higher first ionization energy.

Step 5: Postulate a Reason for the Higher Ionization Energy of Magnesium

The reason for the higher first ionization energy of magnesium compared to sodium can be attributed to their positions in the periodic table as well as their electronic configurations. Magnesium, with an additional proton in its nucleus compared to sodium, experiences a higher effective nuclear charge, which results in it holding its electrons more tightly. As a result, it takes more energy to remove the first electron from magnesium than it does for sodium.

Key Concepts

Periodic Table

The periodic table is a powerful tool for understanding the properties of chemical elements. It is arranged in a way that reveals trends across different elements. These trends tell us a lot about how elements behave. One of the key trends observed is ionization energy, which generally increases as you move from left to right across a period. This means that elements on the right side of a period hold onto their electrons more tightly than those on the left.

The position of an element on the periodic table can also tell us about its atomic structure. For example, magnesium is located to the right of sodium in period 3. This positional information is crucial, as it explains why magnesium has a higher first ionization energy compared to sodium. The configuration and nuclear charge play a big part in this behavior.

Effective Nuclear Charge

Effective nuclear charge is a concept that explains how strongly the positively charged nucleus of an atom can pull on its electrons. Although the number of protons in the nucleus gives an atom its positive charge, not all of this charge can be felt by the outermost electrons. That's because inner electrons partially shield the outer electrons from the full pull of the nucleus.

As you move across a period in the periodic table, the effective nuclear charge generally increases. This is because more protons are being added, but the shielding effect does not increase as significantly, leading to a stronger pull on the outer electrons. This results in higher ionization energies, as seen in magnesium compared to sodium. Magnesium has a higher effective nuclear charge due to having one more proton than sodium, which makes it harder to remove an electron.

Electron Configuration

Electron configuration describes how electrons are distributed in an atom's shells and subshells. Knowing an element's electron configuration helps us understand its chemical behavior and properties.

For sodium (Na), the electron configuration is 1s² 2s² 2p⁶ 3s¹, which means it has one electron in its outermost shell. However, magnesium (Mg) has the configuration 1s² 2s² 2p⁶ 3s², filling the same outer shell with two electrons.

This difference is important for explaining ionization energy. Magnesium's fully filled 3s orbital means its electrons are more tightly bound compared to sodium's single electron in the 3s shell. Hence, magnesium's first ionization energy is higher because it requires more energy to remove an electron from a stable, filled shell.

Chemical Elements

Chemical elements are the basic building blocks of matter. Each element is defined by the number of protons in its nucleus, known as the atomic number. Elements are organized in the periodic table not just by their atomic numbers, but also by their recurring chemical properties.

Ionization energy, like with magnesium and sodium, is one such property that can help predict how an element might react chemically. Elements in the same group often have similar chemical behaviors due to having a similar number of electrons in their outer shell. However, comparing elements like magnesium and sodium across a period can illustrate trends in ionization energy and effective nuclear charge.

Understanding the nature of chemical elements and their organization in the periodic table enables us to predict reactions, bond formations, and other chemical properties, making it a fundamental aspect of learning chemistry.