Question

Which element in each of the following pairs has the higher ionization energy?? (a) \(\mathrm{S}\) or \(\mathrm{Cl}\) (b) Si or Ge (c) In or \(\mathrm{O}\)

Short answer

(a) Cl, (b) Si, (c) O

Step-by-step solution

Understanding Ionization Energy

Ionization energy refers to the energy required to remove an electron from an atom in its gaseous state. Generally, ionization energy increases across a period (from left to right) and decreases down a group (from top to bottom) on the periodic table.

Comparing Sulfur and Chlorine

Sulfur \((\mathrm{S})\) and Chlorine \((\mathrm{Cl})\) belong to the same period on the periodic table (Period 3). Since ionization energy increases across a period, Chlorine, which is to the right of Sulfur, will have a higher ionization energy.

Comparing Silicon and Germanium

Silicon \((\mathrm{Si})\) and Germanium \((\mathrm{Ge})\) are in the same group (Group 14) but different periods, with Germanium being below Silicon. Ionization energy decreases as you move down a group, so Silicon will have a higher ionization energy than Germanium.

Comparing Indium and Oxygen

Indium \((\mathrm{In})\) and Oxygen \((\mathrm{O})\) are in different groups and periods. Oxygen is in Period 2, far to the right of Indium in the periodic table. Elements on the right generally have higher ionization energies compared to those on the left, so Oxygen will have a higher ionization energy than Indium.

Key concepts

Periodic Table Trends

Ionization energy is a key concept influenced by periodic table trends. As you move across a period from left to right, ionization energy generally increases. This is because the nuclear charge increases, attracting electrons more strongly, and making them harder to remove.
In contrast, when you move down a group, ionization energy decreases. This is due to the increase in electron shielding and distance from the nucleus, which makes it easier to remove an outer electron. So, understanding these trends can help you predict the ionization energy of elements.

• Across a period: Ionization energy increases.
• Down a group: Ionization energy decreases.

This understanding helps in comparing elements like Sulfur and Chlorine, where Chlorine, being further to the right, has a higher ionization energy.

Atomic Structure

Ionization energy is deeply connected to atomic structure. Atoms consist of a nucleus surrounded by electrons moving in orbitals. The energy needed to remove an electron reflects the atomic structure’s influence.
Each electron experiences a pull from positively charged protons in the nucleus. When an electron is closer to the nucleus, it experiences a stronger attraction, hence a higher ionization energy is needed to remove it.

• Protons and electrons interact strongly when closer.
• Electrons further from the nucleus require less energy to remove.

Therefore, Silicon has a higher ionization energy than Germanium because its electrons are held more tightly due to its smaller atomic size.

Chemical Elements

Understanding chemical elements through the lens of ionization energy reveals intriguing behaviors. Chemical elements are ordered on the periodic table in a way that reflects their properties, including ionization energy.
Elements tend to have similar chemical behavior and trends in ionization energy within the same group and period. For example, Oxygen, with its smaller size and more effective nuclear charge than Indium, requires more energy to remove an electron.

• Element positioning affects ionization energies.
• Periods highlight energy trends effectively.

Knowing the behavior of elements like Indium and Oxygen helps in understanding broader chemical reactivities and tendencies.