Question

a. Distinguish between the first, second, and third ionization energies of an atom. b. How do the values of successive ionization energies compare? c. Why does this occur?

Short answer

First, second, and third ionization energies refer to removing the first, second, and third electrons, respectively. Successive ionization energies increase. This is due to stronger effective nuclear charge on remaining electrons.

Step-by-step solution

- Define First Ionization Energy

The first ionization energy is the energy required to remove the first electron from a neutral atom to form a positive ion. This process can be represented as: \[ \text{X(g)} + \text{ionization energy}_1 \rightarrow \text{X}^+ (g) + e^- \]

- Define Second Ionization Energy

The second ionization energy is the energy required to remove the second electron from the singly charged positive ion to form a doubly charged positive ion. This process can be represented as: \[ \text{X}^+ (g) + \text{ionization energy}_2 \rightarrow \text{X}^{2+} (g) + e^- \]

- Define Third Ionization Energy

The third ionization energy is the energy required to remove the third electron from the doubly charged positive ion to form a triply charged positive ion. This process can be represented as: \[ \text{X}^{2+} (g) + \text{ionization energy}_3 \rightarrow \text{X}^{3+} (g) + e^- \]

- Compare Successive Ionization Energies

The values of successive ionization energies increase. Specifically, the second ionization energy is greater than the first ionization energy, and the third ionization energy is greater than the second ionization energy.

- Explain Why Successive Ionization Energies Increase

This increase occurs because, after each electron is removed, the remaining electrons experience a stronger effective nuclear charge. This means that more energy is required to remove an electron from an increasingly positive ion.

Key concepts

First Ionization Energy

The first ionization energy is the amount of energy required to remove one electron from a neutral atom. This process transforms a neutral atom into a positively charged ion. Imagine you have an atom, designated as X in the gas phase; losing its first electron can be written as: \[ X(g) + \text{ionization energy}_1 \rightarrow X^+ (g) + e^- \] This concept is fundamental in chemistry because it indicates how strongly an electron is bound to the nucleus.

Second Ionization Energy

The second ionization energy refers to the energy needed to remove a second electron after the first one has been taken out. This time, you're starting with a singly charged positive ion. For atom X, it can be shown as: \[ X^+ (g) + \text{ionization energy}_2 \rightarrow X^{2+} (g) + e^- \] So it's essentially the energy required to move from a +1 ion to a +2 ion. Because the atom is already positively charged, the remaining electrons are held tighter, making this process more energy-demanding.

Third Ionization Energy

The third ionization energy is the energy required to remove a third electron, meaning the atom is already in a +2 ion state. The equation would look like this: \[ X^{2+} (g) + \text{ionization energy}_3 \rightarrow X^{3+} (g) + e^- \] Removing this third electron is even more challenging because the electron is being pulled away from an already highly positive ion. This explains why the third ionization energy is considerably higher than both the first and second ionization energies.

Effective Nuclear Charge

Effective nuclear charge (often denoted as \( Z_{eff} \)) plays a crucial role in understanding ionization energies. It measures the net positive charge experienced by electrons in an atom. Each time an electron is removed, the remaining electrons are more strongly attracted to the nucleus due to lesser electron shielding. Consequently, \( Z_{eff} \) increases as more electrons are taken away. This is why removing subsequent electrons requires progressively more energy.

Successive Ionization Energies

Successive ionization energies are the sequence of energies required to remove electrons one after another from an atom.

• First ionization energy is less than the second.
• The second ionization energy is less than the third.
• This pattern continues as more electrons are removed.

The reason behind this increasing trend is the growing effective nuclear charge, making it increasingly difficult to remove each successive electron. Understanding this concept can help clarify why elements behave the way they do, especially in chemical reactions.