Question

Which pair of elements do you expect to be most similar? Why? $$ \begin{array}{l}{\text { a. nitrogen and oxygen }} \\ {\text { b. titanium and gallium }} \\ {\text { c. lithium and sodium }} \\ {\text { d. germanium and arsenic }} \\ {\text { e. } \text { argon and bromine }}\end{array} $$

Short answer

The most similar pair of elements is lithium (Li) and sodium (Na) because they belong to the same group and have similar electron configurations.

Step-by-step solution

Understanding the Periodic Table

To determine which pair of elements is most similar, we must refer to the Periodic Table of Elements. Elements are arranged in periods (horizontal rows) and groups (vertical columns). Elements in the same group generally have similar properties because they have the same number of valence electrons.

Examining the Pairs of Elements

We will look at each pair and determine their positions in the same or different groups and periods. a. Nitrogen (group 15, period 2) and Oxygen (group 16, period 2) - adjacent groups in the same period. b. Titanium (group 4, period 4) and Gallium (group 13, period 4) - not in the same group, same period. c. Lithium (group 1, period 2) and Sodium (group 1, period 3) - same group, subsequent periods. d. Germanium (group 14, period 4) and Arsenic (group 15, period 4) - adjacent groups, same period. e. Argon (group 18, period 3) and Bromine (group 17, period 4) - adjacent groups, different periods.

Identifying the Most Similar Elements

Elements in the same group are more likely to show similar characteristics than elements in the same period because they have similar electron configurations. Therefore, we identify that lithium (Li) and sodium (Na), both being in group 1, will have the most similarities among the given pairs.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in determining an element's chemical properties. These electrons are involved in forming chemical bonds with other atoms. For example, elements in Group 1 of the periodic table—including lithium and sodium—have one valence electron, making them highly reactive and thus, possessing similar chemical behaviors. They both tend to lose one electron to achieve a stable electronic configuration, which is why they react similarly with other elements.

As part of improvement advice for students trying to understand this concept, it’s important to remember that elements with the same number of valence electrons usually show similar reactivity and bonding characteristics because they are trying to either lose, gain, or share electrons to achieve a stable electron configuration akin to noble gases.

Chemical Properties of Elements

The chemical properties of elements are directly influenced by their electron configurations, particularly by the number and arrangement of valence electrons. Elements that have the same number of valence electrons are grouped together in the periodic table and often exhibit similar chemical properties. This is evident in our example exercise, where lithium and sodium, both residing in Group 1, share characteristics such as a single valence electron leading to similar reactions with water, oxygen, and halogens. Even though they are placed in different periods, the shared valence electron count dominates their chemistry.

To enhance conceptual understanding, students should explore how these properties are exhibited in reactions, such as halogens forming salts with alkali metals, and compare those reactions across the elements in the same group.

Group and Period Trend Patterns

In the periodic table, elements are organized into groups and periods which illustrates periodic trends in properties. Group trends are observed down a column, where elements tend to become more metallic and reactive as you move down, owing to the increasing distance of valence electrons from the nucleus. Period trends, on the other hand, are seen across a row, where elements become less metallic and more nonmetallic as you move from left to right.

It is beneficial for a student's deeper comprehension to recognize that, within a group, elements have similar valence electron configurations leading to analogous behavior. Conversely, as you traverse a period, the number of valence electrons increases and therefore, the nature of the elements gradually changes. For instance, lithium and sodium, despite being in different periods, share more commonalities because they fall within the same group and exhibit similar group trends, unlike oxygen and nitrogen which, despite being in the same period, fall under different groups.