Question

Indicate the smallest and the largest species (atom or ion) in the following group: Al atom, F atom, As atom, \(\mathrm{Cs}^{+}\) ion, \(\mathrm{I}^{-}\) ion, \(\mathrm{N}\) atom.

Short answer

From the given group the smallest species is the F atom and the largest is the \(\mathrm{I}^{-}\) ion.

Step-by-step solution

Understanding Atomic Radius Trend

Before diving into solving this problem, you need to understand how atomic radius behaves in the Periodic Table. The atomic radius generally increases as we go down a group due to the increase in quantum level (number of electron shells). It decreases as we move from left to right across a period on the Periodic Table due to higher effective nuclear charge.

Identify the Smallest Species

Given the atomic or ionic species: Al atom, F atom, As atom, \(\mathrm{Cs}^{+}\) ion, \(\mathrm{I}^{-}\) ion, \(\mathrm{N}\) atom. When referring to the Periodic Table, it is seen that Fluorine(F) atom is the furthest to the right and Nitrogen (N) atom is in the same period as Fluorine but to its left. Thus, Fluorine atom will be smaller than Nitrogen. The \(\mathrm{Cs}^{+}\) ion is a cation, meaning it has lost an electron, making it smaller than its parent atom, but still larger than atoms in upper periods. Therefore, the F atom is the smallest among them.

Identify the Largest Species

From the given species, Cesium (\(\mathrm{Cs}^{+}\) ion) belongs to the group which is at the bottom of the Periodic Table, implying it has the largest atomic radius among given atoms. However, the \(\mathrm{I}^{-}\) ion is an anion which means it has gained an electron, increasing repulsion and making it larger than its parent atom. It is larger than the \(\mathrm{Cs}^{+}\) ion, thus making it the largest species in this group.

Key concepts

Atomic Radius

The atomic radius is the distance from the center of an atom's nucleus to the outermost electron cloud. This measurement indicates the size of the atom. Several factors influence the atomic radius, mainly where the atom is located on the Periodic Table.

• As you move down a group in the Periodic Table, the atomic radius increases. This happens because each new row on the table adds another electronic shell around the nucleus.
• As you move across a period from left to right, the atomic radius decreases. More protons are added to the nucleus, which increases the positive charge. This increased positive charge pulls the electron clouds closer to the nucleus.

The trend in the atomic radius is key to predicting how large or small an atom will be when compared to others. It's particularly useful when comparing species like the Al, F, As, and N atoms in our example.

Ions

Ions are atoms or molecules that have gained or lost electrons and thus have a net electrical charge. Losing electrons forms positively charged ions called cations, while gaining electrons forms negatively charged ions called anions.

• Cations are smaller than their neutral atoms because losing electrons results in a decrease in electron-electron repulsions and the electron cloud contracts further towards the nucleus.
• Anions are larger than their neutral atoms, as gaining extra electrons increases electron-electron repulsions, which makes the outer shell swell.

In our exercise, \(\mathrm{Cs}^{+}\) is a cation, smaller than the neutral cesium atom, and \(\mathrm{I}^{-}\) is an anion, larger than neutral iodine.

Effective Nuclear Charge

The effective nuclear charge (\(Z_{eff}\)) is the net positive charge experienced by an electron in an atom. It's the "pull" felt by the outermost electrons towards the nucleus, considering the shielding caused by inner electrons. This concept is vital in understanding periodic trends like atomic radius and ionization energy.

• The more protons in the nucleus, the greater the pull on the electrons (\(Z_{eff}\) increases).
• Moving left to right across a period increases \(Z_{eff}\) because the number of protons increases, whereas the number of shielding electrons changes only slightly.

In the given problem, Fluorine has a higher effective nuclear charge compared to nitrogen because it has more protons, thus, making it smaller in size.

Periodic Table

The Periodic Table is a systematic arrangement of elements in rows and columns based on their atomic number, electron configuration, and recurring chemical properties. It's an essential tool for chemists to understand elements' characteristics and their relationships to one another.

• Groups are the vertical columns and indicate elements with similar chemical behaviors.
• Periods are the horizontal rows, and moving across a period shows significant changes in properties like atomic radius, electronegativity, and ionization energy.

Utilizing the Periodic Table, one can predict which atoms may be smaller or larger in size, how ions behave, and where trends such as effective nuclear charge arise. In our group of species, understanding their position on the table helps explain the varying sizes observed.