Question

Without using Fig. 8.3, predict the order of increasing electronegativity in each of the following groups of elements. a. \(\mathrm{Na}, \mathrm{K}, \mathrm{Rb} \quad\) c. \(\mathrm{F}, \mathrm{Cl}, \mathrm{Br}\) b. \(\mathrm{B}, \mathrm{O}, \mathrm{Ga} \qquad\) d. \(\mathrm{S}, \mathrm{O}, \mathrm{F}\)

Short answer

The order of increasing electronegativity for each group of elements is: a. \(Na > K > Rb \) b. \(Ga < B < O\) c. \(F > Cl > Br \) d. \(S < O < F\)

Step-by-step solution

a. Na, K, Rb

First, observe that all three elements, Sodium (Na), Potassium (K), and Rubidium (Rb) are in the same group (Group 1: Alkali metals) and are placed one below the other in the periodic table. As we move down a group, electronegativity decreases. Therefore, the order should follow this trend: \[Na > K > Rb \]

b. B, O, Ga

Boron (B), Oxygen (O), and Gallium (Ga) are elements in different groups and periods of the periodic table: B is in Group 13, O is in Group 16, and Ga is in Group 13, below B. First, we'll compare B and Ga. As we move down a group, electronegativity decreases: \[ B > Ga \] Now, we should compare these elements to oxygen. Moving across the periodic table from B to O, electronegativity increases, so we have: \[B < O\] and since \(B > Ga\) \[Ga < O\] Based on our comparisons, the order of increasing electronegativity is: \[Ga < B < O\]

c. F, Cl, Br

Fluorine (F), Chlorine (Cl), and Bromine (Br) are all in the same group (Group 17: Halogens) and are placed one below the other in the periodic table. As we move down a group, electronegativity decreases. Therefore, the order should follow this trend: \[F > Cl > Br \]

d. S, O, F

Sulfur (S), Oxygen (O), and Fluorine (F) are elements of different groups but from the same period in the periodic table (Period 2). When we move across the periodic table from left to right, electronegativity increases. So, the order of increasing electronegativity should follow this trend: \[S < O < F\] So, the order of increasing electronegativity for each group of elements is: a. \(Na > K > Rb \) b. \(Ga < B < O\) c. \(F > Cl > Br \) d. \(S < O < F\)

Key concepts

Periodic Table

The periodic table is an essential tool in chemistry. It provides a systematic way to organize elements based on their properties. Each element is arranged by its atomic number, which is the number of protons in its nucleus. The table is structured into rows called periods and columns called groups or families.

• Periods are the horizontal rows, and they indicate elements with the same number of energy levels.
• Groups are the vertical columns, and elements in the same group have similar chemical properties due to having the same number of valence electrons.

Understanding these placements aids in predicting how an element will react and its properties, such as electronegativity. The layout of the periodic table helps illustrate trends in behaviors like reactivity, electronegativity, and atomic size.

Trends in Electronegativity

Electronegativity is a measure of an atom's ability to attract and bond with electrons. It's an important concept because it helps predict how atoms will interact in chemical compounds.

• Electronegativity values increase as you move from left to right across a period on the periodic table. This is due to increased nuclear charge as more protons are added, which pulls electrons closer.
• As you move down a group, electronegativity generally decreases. The added energy levels increase the distance between the nucleus and the valence electrons, reducing the nucleus's pull on these electrons.

This understanding is crucial for predicting the behavior of elements like in our original exercise. For example, fluorine is the most electronegative element, which is why it outranks others like chlorine and bromine.

Alkali Metals

Alkali metals belong to Group 1 of the periodic table. This group includes elements like sodium (Na), potassium (K), and rubidium (Rb). These elements share some common characteristics.

• They have a single electron in their outermost shell, making them highly reactive, especially with water.
• As you move down the group from sodium to rubidium, these elements become more reactive and their electronegativity decreases. This occurs because the outer electron is further from the nucleus and experiences less attraction.

Due to these trends, in electronegativity, sodium is more electronegative than potassium, which is more electronegative than rubidium.

Halogens

Halogens make up Group 17 in the periodic table, consisting of elements like fluorine (F), chlorine (Cl), and bromine (Br). These elements are highly reactive nonmetals.

• Halogens have seven electrons in their outer shell, making them very electronegative as they seek one additional electron to achieve a stable configuration.
• Fluorine is the most electronegative element in the entire periodic table because it is closest to having a full valence shell.
• Electronegativity decreases as you move from fluorine to chlorine to bromine. This trend is due to the increased distance from the nucleus as more energy levels are added down the group, weakening the nuclear attraction.

Understanding these properties is essential for predicting chemical behavior and the formation of compounds.