Which of the ions Se2-, F-, O2-, and Rb+ has the largest radius?

Verified step by step guidance

Step 1: Understand that ionic radius is influenced by the number of electrons and the effective nuclear charge. Ions with more electrons than protons tend to have larger radii due to increased electron-electron repulsion.

Step 2: Identify the electron configuration of each ion: Se2- has gained 2 electrons, F- has gained 1 electron, O2- has gained 2 electrons, and Rb+ has lost 1 electron.

Step 3: Compare the number of electrons in each ion: Se2- has 36 electrons, F- has 10 electrons, O2- has 10 electrons, and Rb+ has 36 electrons.

Step 4: Consider the effective nuclear charge: Se2- and Rb+ have the same number of electrons, but Rb+ has a higher nuclear charge due to more protons, pulling the electrons closer and reducing its radius.

Step 5: Conclude that Se2- has the largest radius because it has the same number of electrons as Rb+ but a lower effective nuclear charge, resulting in a larger ionic radius.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ionic Radius

Ionic radius refers to the size of an ion in a crystal lattice. It is influenced by the ion's charge and the number of electrons relative to protons. Cations (positively charged ions) are generally smaller than their neutral atoms due to the loss of electrons, while anions (negatively charged ions) are larger due to the addition of electrons, which increases electron-electron repulsion.

Effective Nuclear Charge

Effective nuclear charge (Z_eff) is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the shielding effect of inner electrons that reduces the full nuclear charge felt by outer electrons. A higher Z_eff typically results in a smaller ionic radius, as the increased attraction pulls electrons closer to the nucleus.

Trends in Ionic Size

Ionic size trends can be observed in the periodic table, where ionic radii increase down a group and decrease across a period. For anions, larger negative charges lead to larger radii, while for cations, increased positive charge results in smaller radii. Understanding these trends helps in comparing the sizes of different ions, such as Se2-, F-, O2-, and Rb+.