Question

Lithium and magnesium exhibit diagonal relationship because (1) both possess nearly the same size (2) both possess similar electronic configuration (3) both occur together in nature (4) both have same number of valence electrons

Short answer

Option (1): Both possess nearly the same size.

Step-by-step solution

Understand the diagonal relationship in the periodic table

In the periodic table, elements in the second period show similarities with elements in the third period of the following group. This relationship is often referred to as a diagonal relationship. For example, lithium (Li) can show similarities to magnesium (Mg).

Analyze the options based on the concept of diagonal relationship

Evaluate each option to see how it corresponds to the concept: (1) Both possess nearly the same size: Although not exactly the same, they have comparable ionic radii. (2) Both possess similar electronic configuration: The configuration isn’t very similar; lithium is 1s²2s¹ and magnesium is 1s²2s²2p⁶3s². (3) Both occur together in nature: Elements do not necessarily need to co-occur. (4) Both have same number of valence electrons: Lithium has 1 valence electron and magnesium has 2, this does not hold true.

Conclusion

Based on the analysis, the best explanation for the diagonal relationship between lithium and magnesium is (1) both possess nearly the same size due to comparable ionic radii.

Key concepts

Periodic Table

The periodic table is a systematic arrangement of elements based on their atomic numbers, electron configurations, and recurring chemical properties.
Each element is positioned in a specific location, forming rows called periods and columns known as groups.
The elements in the periodic table can exhibit patterns or relationships known as periodicity.
One of these unique patterns is the diagonal relationship, where elements in neighboring groups and periods show similar properties, like lithium (Li) and magnesium (Mg).
This relationship often occurs due to similar ionic sizes and comparable charge densities.

Ionic Radii

Ionic radii refer to the size of an ion, which is an atom or molecule with an electric charge due to the loss or gain of electrons.
When comparing elements like lithium and magnesium, their comparable ionic radii play a significant role in their diagonal relationship.
While not exactly the same, the sizes of Li+ and Mg2+ are close enough that certain properties, like charge density, are similar.
This size similarity is primarily responsible for their chemical resemblances and why they can be referenced together when discussing diagonal relationships.
Thus, despite being in different periods and groups, these elements can have analogous behaviors due to their ionic sizes.

Electronic Configuration

Electronic configuration describes the distribution of electrons in an atom’s orbitals.
For instance, lithium has an electronic configuration of 1s²2s¹, while magnesium is 1s²2s²2p⁶3s².
While these configurations aren’t exactly similar, key elements like outer electrons contribute to their diagonal relationship.
Even though their outer electrons occupy different energy levels, their positions in similar regions of the periodic table link them in terms of chemical behavior.
This illustrates how electronic configuration, when combined with ionic sizes, supports the diagonal relationship.
Hence, studying these configurations helps to understand how different elements share chemical properties despite differences in their positioning within the periodic table.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom, crucial in determining chemical properties and reactivity.
Lithium has one valence electron in its 2s orbital, whereas magnesium has two valence electrons in the 3s orbital.
Despite this difference, the significance lies in how valence electrons affect chemical bonding and reactions.
Lithium tends to lose one electron to achieve a stable configuration, forming a Li+ ion, while magnesium loses two, forming an Mg2+ ion.
Understanding the role of valence electrons is key to grasping concepts like the diagonal relationship, where elements exhibit similar reactivity despite having a varying number of valence electrons.
Recognizing these dynamics aids in comprehensively studying and predicting chemical behaviors in related elements.