Question

For each of the following sets of elements, arrange in order of increasing atomic radius: a) \(\mathrm{Na}, \mathrm{Li}, \mathrm{Rb}, \mathrm{K}\) b) \(\mathrm{Li}, \mathrm{O}, \mathrm{C}, \mathrm{F}\) c) \(\mathrm{Cl}, \mathrm{Br}, \mathrm{I}, \mathrm{F}\)

Short answer

a) Li < Na < K < Rb b) F < O < C < Li c) F < Cl < Br < I

Step-by-step solution

Identify Elements and Their Positions

First, list the elements mentioned in the exercise and identify their respective positions on the periodic table. For this exercise: - Part (a): Na, Li, Rb, K are all alkali metals found in Group 1 of the periodic table. - Part (b): Li, O, C, F are located in periods 2 and 3 across Groups 1, 14, 16, and 17. - Part (c): Cl, Br, I, F are halogens found in Group 17.

Understand Atomic Radius Trend within Groups

Atomic radius increases as you move down a group in the periodic table due to the addition of electron shells. For alkali metals and halogens: - For Group 1 alkali metals (part a): Rb > K > Na > Li. - For Group 17 halogens (part c): I > Br > Cl > F.

Understand Atomic Radius Trend within Periods

Across a period, atomic radius decreases as you move from left to right across the periodic table because of increased nuclear charge without additional shielding. For the elements in period 2: - For part (b): Li > C > O > F.

Arrange Elements for Each Part

Given the trends identified in previous steps, arrange the elements according to increasing atomic radius for each set: - Part (a): Li < Na < K < Rb - Part (b): F < O < C < Li - Part (c): F < Cl < Br < I

Key concepts

Periodic Table

The periodic table is a fundamental tool in chemistry, organizing elements in rows and columns based on increasing atomic number and similar chemical properties. Each column, known as a group, contains elements with similar chemical behaviors due to having the same number of electrons in their outermost shell. Similarly, rows, or periods, reflect elements with the same number of electron shells orbiting the nucleus.
This arrangement allows chemists to easily predict the properties of elements, such as their atomic radius, electronegativity, and more. Group 1, for instance, includes alkali metals like sodium (Na) and lithium (Li), known for their high reactivity. Group 17 is home to halogens like fluorine (F) and chlorine (Cl), which are highly reactive nonmetals.
Understanding the periodic table layout is key to comprehending how elements interact, form compounds, and the underlying trends in their properties.

Trends in Atomic Properties

Atomic properties such as atomic radius, ionization energy, and electronegativity exhibit clear trends across periods and groups in the periodic table. Atomic radius, the focus for many exercises, describes the size of an atom from its nucleus to its furthest electron shell.
A crucial trend is that as you move down a group, the atomic radius increases. This increase is due to the addition of electron shells, which outweigh the increased nuclear charge. Conversely, as you move from left to right across a period, atomic radius decreases. This happens because, within a given period, each succeeding element has a greater positive charge in its nucleus, pulling electrons tighter and decreasing atomic size.
These trends are vital for predicting how elements behave and interact in chemical reactions, underpinning much of chemical education.

Alkali Metals

Alkali metals, found in Group 1 of the periodic table, include elements such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and others. These metals are characterized by having a single electron in their outermost shell, making them highly reactive, particularly with water.
Their reactivity increases as you move down the group: lithium being the least and francium the most reactive, due to increasing atomic size and the decreasing hold of the nucleus on the outer electron. This trend also affects their atomic radius which increases down the group due to the addition of electron shells.
Alkali metals display metallic properties such as electrical conductivity and luster, and they form strong bases when combined with water, thus the name 'alkali' metals.

Halogens

Halogens are elements found in Group 17 of the periodic table and include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Known for their high reactivity, particularly with alkali metals to form salts, halogens are unique because they attain stability by gaining a single electron to complete their outer shell.
This results in distinct trends in their properties. Like atomic radius, which increases down the group as additional electron shells are added, making iodine (I) larger in size compared to fluorine (F). However, their electronegativity, which is a measure of an atom's ability to attract electrons, decreases down the group.
Understanding these properties of halogens is pivotal for predicting their behavior in chemical reactions and their role in forming compounds like salts and acids.