Problem 40 - Chemistry The Central Science In Si Units

Question

Identify each statement as true or false: (a) Ionization energies are always endothermic. (b) Potassium has a larger first ionization energy than lithium. (c) The second ionization energy of the sodium atom is larger than the second ionization energy of the magnesium atom. (d) The third ionization energy is three times the first ionization energy of an atom.

Step-by-Step Solution

Answer

(a) True, (b) False, (c) True, (d) False

Step 1: Understanding Ionization Energies

Ionization energy is the energy required to remove an electron from a neutral atom in the gas phase. This process always requires energy input to overcome the attraction between the electron and the nucleus, making it an endothermic process. Therefore, statement (a) is true.

Step 2: Comparing First Ionization Energies of Potassium and Lithium

The first ionization energy generally increases across a period and decreases down a group in the periodic table. Potassium (K) is below lithium (Li) in the same group and therefore has a smaller first ionization energy because the outer electron is further from the nucleus and less tightly held. Thus, statement (b) is false.

Step 3: Evaluating Second Ionization Energies of Sodium and Magnesium

The second ionization energy refers to the removal of a second electron. After one electron is removed from sodium (Na), its electronic configuration becomes like that of neon, resulting in a very high second ionization energy. Magnesium (Mg) after losing one electron has the configuration similar to Na, so it is easier to remove a second electron from Mg than from Na. Thus, statement (c) is true.

Step 4: Understanding the Relationship Between Successive Ionization Energies

Successive ionization energies increase due to the increased positive charge attracting the remaining electrons more strongly. However, there's no set ratio like 1:3 for third to first ionization energies. The increase in energy depends on electronic configuration and resultant stability, not a simple tripling. Therefore, statement (d) is false.

Key Concepts

Endothermic Process

Ionization energy is required to remove an electron from an atom or ion, and this process is always endothermic. This means energy must be supplied to the atom to remove the electron, as the attraction between the negatively-charged electron and the positively-charged nucleus must be overcome. The energy input essentially breaks the bond between the electron and nucleus.

Because the electron is affected by the attractive forces of the nucleus, detaching it is like climbing uphill energetically, requiring an investment of energy. Ionization processes are thus inherently endothermic, leading to an important understanding: in chemistry, when something is endothermic, it absorbs energy from its surroundings. This is in contrast to exothermic processes, which release energy.

Periodic Table

The periodic table is an invaluable tool in chemistry, organizing elements by increasing atomic number and similar properties. Understanding the trends in the periodic table can help you predict the behavior of elements, including their ionization energies.

- Ionization energy generally increases across a period from left to right. This is because the number of protons in the nucleus increases, pulling the electrons closer and making them harder to remove. - Conversely, ionization energy decreases down a group. As you move down a group, electrons occupy higher energy levels and are further from the nucleus. This reduces the nuclear attraction, making the electrons easier to remove.

This explains why potassium (K) has a lower first ionization energy than lithium (Li), despite being lower on the table. Potassium's outer electrons are further from the nucleus and thus less tightly bound.

Electronic Configuration

Electronic configuration refers to the distribution of electrons in an atom's orbitals, which influences ionization energy significantly. When electrons are removed from an atom, its electronic configuration changes, often leading to changes in ionization energies.

For example, sodium (Na) has an electronic configuration of \([Ne] 3s^1\) and once it loses one electron, it reaches the stable configuration of neon \([Ne]\). This results in a very high second ionization energy because removing another electron would disrupt this stable configuration.

In magnesium (Mg), losing one electron gives a configuration similar to that of sodium \([Ne] 3s^1\), so while the first ionization energy is reasonably high, the second ionization is comparatively easier than in sodium, underscoring the influence of electronic configuration.

Successive Ionization Energies

Successive ionization energies refer to the energies required to remove subsequent electrons from an atom or ion. Each successive electron removal requires more energy than the last because the nuclear attraction is exerted on fewer electrons, increasing the effective nuclear charge experienced by each electron.


A common misconception is that successive ionization energies increase by fixed multiples, but this is not the case. The exact increase depends on several factors:

• Electronic configuration: Stability of configurations (like noble gas configurations) result in significant jumps in ionization energy.
• Effective nuclear charge: With each electron removed, the remaining electrons experience a stronger attraction to the nucleus.

Understanding these principles can help dispel myths such as the idea that the third ionization energy is merely triple the first; the reality is much more nuanced and depends on the atom's specific electronic structure at each stage.