Question

In each of the following groups, which element is the most electronegative? Which is the least electronegative? a. $\mathrm{K},\mathrm{Na},\mathrm{H}$ b. $\mathrm{F},\mathrm{Br},\mathrm{Na}$ c. B , N , F

Short answer

The most and least electronegative elements are as follows: a. Most electronegative: $\mathrm{H}$, Least electronegative: $\mathrm{K}$ b. Most electronegative: $\mathrm{F}$, Least electronegative: $\mathrm{Na}$ c. Most electronegative: $\mathrm{F}$, Least electronegative: $\mathrm{B}$

Step-by-step solution

Determine the periods and groups of the given elements

Refer to the periodic table to find the period number (horizontal row) and group number (vertical column) of each element in the given groups. Here are the period and group numbers for the given elements: - $\mathrm{K}$ (Period 4, Group 1), $\mathrm{Na}$ (Period 3, Group 1), $\mathrm{H}$ (Period 1, Group 1) - $\mathrm{F}$ (Period 2, Group 17), $\mathrm{Br}$ (Period 4, Group 17), $\mathrm{Na}$ (Period 3, Group 1) - $\mathrm{B}$ (Period 2, Group 13), $\mathrm{N}$ (Period 2, Group 15), $\mathrm{F}$ (Period 2, Group 17)

Apply the general trend of electronegativity

As electronegativity increases from left to right across a period and decreases down a group, we can compare the elements within each group: a. Since all elements are in Group 1, we can compare their electronegativity based on their period numbers. $\mathrm{H}$ is in Period 1, $\mathrm{Na}$ is in Period 3, and $\mathrm{K}$ is in Period 4. Therefore, $\mathrm{H}$ is the most electronegative and $\mathrm{K}$ is the least electronegative in this group. b. In this group, $\mathrm{F}$ (Period 2 , Group 17) has the highest electronegativity due to its position furthest to the right, and $\mathrm{Na}$ (Period 3, Group 1) has the lowest electronegativity since it is furthest to the left and down. c. Similarly, in this group, $\mathrm{F}$ (Period 2 , Group 17) has the highest electronegativity due to its position furthest to the right, and $\mathrm{B}$ (Period 2 , Group 13) has the lowest electronegativity since it is furthest to the left. Now we have identified the most and least electronegative elements in each group. The results are as follows: a. Most electronegative: $\mathrm{H}$, Least electronegative: $\mathrm{K}$ b. Most electronegative: $\mathrm{F}$, Least electronegative: $\mathrm{Na}$ c. Most electronegative: $\mathrm{F}$, Least electronegative: $\mathrm{B}$

Key concepts

Periodic Table

The periodic table is like a map of chemical elements. It organizes all known elements based on their atomic number, which is the number of protons in an atom. The layout is carefully designed to show connections and patterns.
You might notice that the table is divided into periods and groups. **Periods** are the horizontal rows, and each period indicates a new layer of electrons around the atomic nucleus. As you move left to right across a period, elements generally become less metallic and more non-metallic.
**Groups** are the vertical columns, and they often share similar chemical properties. For example, Group 1 elements, known as alkali metals, are highly reactive, while Group 17 elements, the halogens, are very electronegative and reactive non-metals.

• Groups indicate the number of valence electrons (electrons in the outermost shell).
• Periods signify the increasing energy levels or electron shells.

This structure helps predict how elements might bond or react with each other.

Chemical Elements

Chemical elements are pure substances consisting of only one type of atom. Every element has its own place on the periodic table and is identified by a unique symbol, such as $\mathrm{H}$ for hydrogen or $\mathrm{F}$ for fluorine.
Each element is characterized by its atomic number, which tells us the number of protons in its nucleus. This atomic number also identifies the element's position on the periodic table.
Basic knowledge about elements includes understanding:

• Atomic Structure: Protons, neutrons, and electrons make up atoms.
• Isotopes: Atoms with the same number of protons but different numbers of neutrons.
• Chemical Properties: These are determined by an element's electron configuration.

Elements combine in various ways to form compounds, which are essential for the vast diversity of materials and substances we encounter every day.

Trends in Electronegativity

Electronegativity is a measure of how strongly an atom attracts electrons in a bond. Understanding trends in electronegativity helps predict how elements will interact in chemical reactions.
Across the periodic table, electronegativity follows a clear pattern. Here’s how:

• Increases Across a Period: From left to right across a period, electronegativity tends to increase. This is because the number of protons increases, attracting electrons more strongly.
• Decreases Down a Group: As you move down a group, electronegativity decreases. Electrons are further from the nucleus and are shielded by additional electron shells, reducing attraction.

Fluorine ($\mathrm{F}$) is the most electronegative element, making it very effective at attracting electrons in chemical bonds.
These trends help determine which elements are more likely to gain or lose electrons, influencing their chemical behavior and forming the backbone of many chemical reactions.