Question

A good electron thief needs a trap at low energy to entice its prey. A poor electron shepherd will have at least some of its tlock dangling out at high energy. Consider rows 2 and 5 in the periodic table. Why should fluorine, in row \(2,\) be more reactive than iodine. in row 5 , while lithium, in row 2 , is less reactive than \mathrm{\\{} u b i d i u m , ~ i n ~ r o w ~ 5 ?

Short answer

Fluorine is more reactive than Iodine because as you move up in the group, reactivity increases dues to stronger nuclear control of the outer shell electrons. Conversely, Rubidium is more reactive than Lithium because as you move down the group, reactivity increases due to less nuclear control of the outer shell electrons.

Step-by-step solution

Understanding Reactivity of Fluorine and Iodine

Fluorine and iodine are both in the 17th group (halogens) but in different periods (rows) of the periodic table. Fluorine is in the 2nd period, while iodine is in the 5th. In the halogens, reactivity decreases as you move down the group because as you go down the group, the atomic radius increases, which increases the distance between the nucleus and the outer electron shell. This allows for less nuclear control over the ourter shell electrons, hence the reactivity decreases.

Understanding Reactivity of Lithium and Rubidium

Lithium and Rubidium are both in group 1 (alkali metals) but in a different period. Lithium is in the 2nd period while Rubidium is in the 5th period. In alkali metals, reactivity increases as you move down the group. This is due to the increase in atomic radius and the electrons in the outer shell being further from the nucleus, thus less controlled by the nucleus, which results in a increased reactivity.

Concluding Reasons to the Problem

Therefore, it can be concluded that Fluorine is more reactive than Iodine due to its smaller atomic radius allowing for greater control over outer shell electrons. However, Rubidium is more reactive than Lithium due to its larger atomic radius allowing for less control over its the outer shell electrons.

Key concepts

Periodic Table

The periodic table is an organized structure that displays all known chemical elements. Elements are arranged in order of increasing atomic number, which is the number of protons in an atom's nucleus. This arrangement not only helps us understand more about the individual properties of elements but also predicts how they will react with one another.

• Each horizontal row in the periodic table is referred to as a "period." As you move across a period from left to right, properties such as electronegativity and ionization energy usually increase.
• Vertical columns are known as "groups." Elements within the same group typically share similar properties because they have the same number of electrons in their outer shell.

Understanding the structure of the periodic table helps us predict the reactivity of elements, which is crucial for explaining why certain elements like fluorine and lithium react the way they do in comparison to iodine and rubidium.

Atomic Radius

The atomic radius is a term that describes the size of an atom. Specifically, it is half the distance between the centers of two identical atoms that are bonded together. This concept plays a key role in determining reactivity.

• As you move down a group in the periodic table, the atomic radius increases. This occurs because additional electron shells are added, making the atom larger.
• Across a period, atomic radius decreases from left to right. Even though more protons and electrons are added, the increased nuclear charge pulls electrons closer in, reducing the size.

When considering reactivity, elements with smaller atomic radii tend to be more reactive in groups like halogens, because their outer electrons are closer to the nucleus and more tightly controlled. On the other hand, in groups like alkali metals, a larger atomic radius means electrons are held more loosely, increasing reactivity.

Halogens

Halogens are located in Group 17 of the periodic table and include elements like fluorine and iodine. They are known for their high reactivity, especially fluorine, which is the most reactive of all.

• The reactivity of halogens decreases as you move down the group. This is because the atomic radius increases, thus the outer electrons are further from the nucleus and less tightly held.
• Halogens readily gain electrons to fill their outer shell, achieving a stable electron configuration. This tendency makes them very effective at "stealing" electrons from other elements.

In comparing fluorine and iodine, fluorine's smaller atomic radius means it can more forcefully attract an electron compared to iodine, making it more reactive.

Alkali Metals

Alkali metals are found in Group 1 of the periodic table, including elements like lithium and rubidium. They are characterized by having a single electron in their outermost shell.

• The reactivity of alkali metals increases as you move down the group because the atomic radius increases, which means the outermost electron is farther from the nucleus and easier to remove.
• Alkali metals tend to lose their single outer electron readily, which leads to their high reactivity, especially when reacting with water or other substances.

In a comparison of lithium and rubidium, rubidium, being lower on the periodic table, has a larger atomic radius than lithium. This property means rubidium's electrons are less tightly bound, making it more reactive.