Problem 76 - Chemistry Matter and Change

Question

Do you expect cesium, a group 1 element used in infrared lamps, or bromine, a halogen used in firefighting compounds to have the greatest electronegativity? Why?

Step-by-Step Solution

Answer

Bromine has the greater electronegativity compared to cesium, as it is further to the right and higher up within the periodic table. Electronegativity increases across a period (left to right) and decreases down a group (top to bottom). Bromine's position, being closer to the top-right corner of the table, indicates higher electronegativity.

Step 1: Define electronegativity

Electronegativity is the ability of an atom in a molecule to attract electrons towards itself. It depends on factors like atomic number and atomic radius. In general, electronegativity increases across a period from left to right and decreases down a group in the periodic table.

Step 2: Locate cesium and bromine on the periodic table

Cesium belongs to group 1 (alkali metals) and is in the 6th period, while bromine belongs to group 17 (halogens) and is in the 4th period.

Step 3: Compare electronegativities based on their positions

Since electronegativity increases across a period (left to right) and decreases down a group (top to bottom), we can make the following comparisons: - Cesium is further to the left than bromine, so bromine is expected to have a higher electronegativity. - Cesium is further down than bromine, so cesium is expected to have a lower electronegativity.

Step 4: Determine the element with the greatest electronegativity

Based on the comparisons made in Step 3, we can conclude that bromine has a greater electronegativity when compared to cesium. This greater electronegativity is due to bromine's position in the periodic table, being closer to the top-right corner where elements generally have higher electronegativities.

Key Concepts

Periodic Table

The Periodic Table is a tabular arrangement of all known chemical elements organized based on their atomic number, electron configuration, and recurring chemical properties. Elements are ordered from left to right and top to bottom by increasing atomic number. This design helps predict the properties of elements, including electronegativity. As you move across a period from left to right, electronegativity tends to increase. This means elements on the right side of the table are generally more electronegative. Conversely, moving down a group (from top to bottom), electronegativity decreases as atoms gain more electron shells, which reduces their ability to attract additional electrons due to the increased distance from the nucleus.

Group 1 Elements

Group 1 elements, also known as alkali metals, include lithium, sodium, potassium, rubidium, cesium, and francium. These elements are located in the far-left column of the periodic table. They are characterized by having one electron in their outermost shell, making them highly reactive, especially with water.

• Alkali metals have low electronegativities because they tend to lose their single valence electron easily to form positive ions.
• Their reactivity increases as you move down the group due to the increasing atomic radius and decreasing ionization energy.

Cesium, for example, has a relatively large atomic size and lower electronegativity compared to other elements in the same period. This is because its outer electron is more easily given up in reactions.

Halogens

Halogens are the elements in Group 17 of the periodic table, which include fluorine, chlorine, bromine, iodine, and astatine. These elements are highly electronegative and tend to gain electrons during chemical reactions.

• They have high electronegativities because of their smaller atomic radii and greater nuclear charge, allowing them to attract electrons strongly.
• Electronegativity decreases as you move down this group from fluorine to astatine because the atomic radius increases, reducing the attractive force exerted by the nucleus on the valence electrons.

Bromine, a halogen, is more electronegative than cesium, an alkali metal. Its position, higher up and to the right of the periodic table, makes it better at attracting electrons.

Atomic Radius

Atomic radius is the distance from the nucleus of an atom to the outermost electron shell. It plays a significant role in determining the chemical properties and reactivity of an element. Generally, the atomic radius:

• Increases as you move down a group due to the addition of extra electron shells.
• Decreases as you move across a period from left to right because additional protons pull the electron cloud closer.

In the context of the exercise, cesium has a larger atomic radius compared to bromine because it is further down in its group. A larger atomic radius in cesium means its outer electrons are further from the nucleus, which contributes to its lower electronegativity compared to bromine.