Problem 38 - Chemistry: The Central Science in SI Units, Global Edition

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) The trend in electronegativity going from left to right in a row of the periodic table is that it increases due to an increased positive charge of the nucleus. (b) Electronegativity values generally decrease going down a column in the periodic table because of the increased shielding effect. (c) False: The most easily ionizable elements are not the most electronegative; in fact, they are less electronegative since they have lower ionization energy.

Step 1: Part (a): Trend in electronegativity going from left to right in a row

Electronegativity is the tendency of an atom to attract a bonding pair of electrons towards itself. As we move from left to right across a period in the periodic table, the number of protons in the nucleus increases, so the positive charge of the nucleus increases. Due to this increase in nuclear charge, the valence electrons are attracted more toward the nucleus and this leads to an increase in electronegativity. Hence, the trend in electronegativity from left to right in a row is that it increases.

Step 2: Part (b): Variation of electronegativity values going down a column

When we go down a group or column in the periodic table, the number of electron shells increases. This results in an increased shielding effect, where the inner electron shells shield the outer valence electrons from the nucleus's positive charge. Due to this shielding effect, the attraction of valence electrons towards the nucleus decreases, and hence the electronegativity decreases. So, the electronegativity values generally decrease going down a column in the periodic table.

Step 3: Part (c): Ionization energy and electronegativity relationship

Ionization energy is the amount of energy required to remove an electron from a neutral atom in its gaseous state. An element with high ionization energy requires more energy to remove an electron, indicating that the electron is held more tightly by the atom, and hence the atom has a higher tendency to attract electrons. On the other hand, elements with lower ionization energy can easily lose electrons. Electronegativity is the ability of an atom to attract electrons towards itself in a chemical bond. Elements with high electronegativity have a stronger pull on electrons in a chemical bond due to their high effective nuclear charge. Statement (c) says: "The most easily ionizable elements are the most electronegative." This statement is false. Since elements with higher ionization energy have a stronger pull on electrons, they are more electronegative. In contrast, more easily ionizable elements, which have lower ionization energy, are less electronegative.

Key Concepts

Periodic Table Trends

The periodic table is designed to showcase elements and their increasing atomic numbers, revealing several patterns known as periodic table trends. One important trend is electronegativity, which reflects how strongly an atom can attract and hold onto electrons. As you move from left to right across a period on the periodic table, the atomic number rises, increasing the nuclear charge. This means that the nucleus has more protons and a greater pull on the electrons. As a result, the electronegativity of the elements tends to increase across a period.

Similarly, when moving down a group, electronegativity usually decreases. This occurs because additional electron shells are added, which places the valence electrons farther from the nucleus where they are less strongly attracted to it. Understanding these trends helps predict how different elements might behave in chemical reactions.

Ionization Energy

Ionization energy is an essential concept in chemistry, representing the energy needed to remove an electron from an atom. Generally, as you move across a period from left to right, ionization energy increases. This is due to the increase in nuclear charge, which means that electrons are more strongly attracted and are harder to remove.

On the other hand, as you move down a column in the periodic table, ionization energy decreases. This is primarily because of electron shielding: additional electron shells shield the valence electrons from the nucleus, making them easier to remove. High ionization energy often corresponds with high electronegativity because both relate to how strongly an atom holds onto its electrons.

Electron Shielding

Electron shielding is a phenomenon that occurs when inner electron shells block the positive charge of the nucleus from the outer valence electrons. This effect makes it so that the pull the nucleus has on valence electrons is reduced, which can influence an atom's electronegativity and ionization energy.

As you progress down a group in the periodic table, electron shielding increases because there are more electron shells. This increased shielding means that outer electrons are less tightly bound to the nucleus. This explains why atoms typically have lower electronegativity and ionization energy as you move down a group, making them more likely to lose electrons in reactions.

Nuclear Charge

Nuclear charge is a key concept in understanding the behavior of elements within the periodic table. It is defined by the number of protons in an atom's nucleus, determining how strongly the nucleus can attract electrons. As you move across a period from left to right, the nuclear charge increases since each successive element has one more proton.

This increase in nuclear charge generally leads to a higher electronegativity, as atoms are able to attract bonding electrons more effectively. It also results in higher ionization energy, as electrons are held more tightly and are harder to remove. Understanding nuclear charge helps in explaining many chemical properties and reactivity patterns of elements.