Problem 38 - Chemistry The Central Science

Question

(a) What is the trend in electronegativity going from left to right in a row of the periodic table? (b) How do electronegativity values generally vary going down a column in the periodic table? (c) True or false: The most easily ionizable elements are the most electronegative.

Step-by-Step Solution

Answer

(a) Electronegativity increases from left to right across a period in the periodic table due to an increase in the number of protons and a decrease in atomic radius. (b) Electronegativity decreases as we move down a column in the periodic table because of the increase in atomic radius and the electrons being farther away from the nucleus. (c) False. The most easily ionizable elements have low electronegativity as they can readily lose electrons, whereas highly electronegative elements have a greater tendency to attract electrons.

Step 1: Part (a): Electronegativity trend in a row of the periodic table

Electronegativity generally increases as we move from left to right across a period in the periodic table. This is because the number of protons in the nucleus increases, leading to a stronger positive charge which attracts the electrons more strongly. Additionally, the atomic radius decreases as we move across a period, causing the electrons to be closer to the nucleus. The overall effect is an increase in the tendency to attract a bonding pair of electrons, resulting in a higher electronegativity value.

Step 2: Part (b): Electronegativity trend in a column of the periodic table

As we move down a column or group in the periodic table, electronegativity generally decreases. This occurs because the atomic radius increases as more energy levels are added to the electron configuration. With larger atomic radii, the electrons are farther away from the nucleus and less attracted by the positive charge of the protons. Consequently, the tendency of an atom to attract a bonding pair of electrons is weaker, leading to lower electronegativity values.

Step 3: Part (c): Checking the validity of the statement

The statement "The most easily ionizable elements are the most electronegative" is false. In fact, it's quite the opposite. The most easily ionizable elements are those with low electronegativity. When an element is easily ionizable, it means that it has a low ionization energy and can readily lose electrons to form a positive ion (cation). On the other hand, highly electronegative elements have a greater tendency to attract electrons and generally do not lose electrons easily. To further support this claim, consider that the most easily ionizable elements are usually found in Group 1 (alkali metals) of the periodic table, while the most electronegative elements are found in Group 17 (halogens). So, the statement is incorrect.

Key Concepts

Periodic Table Trends

The periodic table, arranged by increasing atomic number, showcases several key trends as you move across periods (rows) and down groups (columns). These trends help predict how elements will react chemically and physically. One notable trend is electronegativity.
Electronegativity tends to increase as you move from left to right across a period. This is because, with each additional element, the number of protons in the nucleus increases, which enhances the nucleus's ability to attract electrons. Consequently, elements on the right, like fluorine, tend to have higher electronegativity values.
In contrast, moving down a group, electronegativity decreases. As you go down, the added electron shells result in a larger atomic radius, weakening the nucleus's attraction to electrons due to the increased distance between them. Thus, even though these atoms have more protons, the effect is diluted over the increased distance.

Atomic Radius

The atomic radius is a measure of the size of an atom. It gets influenced by the number of electron shells and how strongly the outermost electrons are attracted to the nucleus.
As you move across a period from left to right, the atomic radius decreases. Even though the number of electrons increases, they are added to the same shell, while the increasing number of protons pulls the electron cloud closer to the nucleus.
However, as you go down a group, the atomic radius increases. This happens because each row downwards adds a new electron shell, increasing the distance between the outer electrons and the nucleus, resulting in a larger atomic size.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom. It is a key factor in determining an element's reactivity and chemical properties.
Across a period from left to right, ionization energy generally increases. This is due to higher nuclear charge pulling the electrons closer, meaning more energy is needed to remove an electron. Atoms on the right side, like noble gases, have high ionization energies because they are close to achieving their full valence electron configurations.
As we move down a group, ionization energy decreases. The outermost electrons are further from the nucleus due to additional electron shells, and are less tightly bound, making them easier to remove. This explains why alkali metals, found at the start of groups, are highly reactive—they have low ionization energies and easily lose electrons.