Question

Which of the following statements is TRUE about the density of alkali metals and alkaline earth metals? A. Alkaline earth metals are less dense because they contain unfilled subshells. B. Alkaline earth metals are less dense because their nuclei contain fewer neutrons. C. Alkali metals are less dense because they contain fewer orbitals. D. Alkali metals are less dense because they have a loosely bound electron in their outer shell.

Short answer

D. Alkali metals are less dense because they have a loosely bound electron in their outer shell.

Step-by-step solution

- Understand what density relates to

Density is the mass per unit volume of a substance. Metals with greater mass and tighter atomic packing are generally denser.

- Analyze the structure of alkali metals

Alkali metals have a single electron in their outer shell, which is loosely bound. This means their atomic structure is less compact, and they often exhibit lower densities.

- Analyze the structure of alkaline earth metals

Alkaline earth metals have two electrons in their outer shell, and their atomic structure is more compact compared to alkali metals. This generally makes them denser.

- Evaluate the given statements

Given these points, we examine the options: A. Unfilled subshells do not affect density in this context significantly. B. The number of neutrons does not directly determine density here. C. Fewer orbitals are not the direct reason for lower density in alkali metals. D. Alkali metals being less dense due to a loosely bound outer electron fits the explanation.

- Conclusion

Based on the above analysis, the correct statement that explains the density difference between alkali metals and alkaline earth metals is option D.

Key concepts

Atomic Structure

To fully grasp why alkali and alkaline earth metals have different densities, it's essential to understand their atomic structures. An atom consists of a nucleus (with protons and neutrons) surrounded by electrons in various orbitals.
The configuration of these electrons plays a crucial role in determining the atom's properties, including density.

• Alkali metals, such as lithium, sodium, and potassium, have a single electron in their outermost orbital.
• Alkaline earth metals, such as magnesium, calcium, and barium, have two electrons in their outermost orbital.

The more compact an atom's electron structure, the more tightly its atoms can pack together, increasing density.

Density

Density is a measure of mass per unit volume. It's calculated using the formula:
\(\text{Density} = \frac{\text{Mass}}{\text{Volume}}\).
For metals, greater mass and tighter atomic packing lead to higher density. Factors influencing density include atomic mass and the spatial arrangement of atoms.
Alkali metals have lighter atoms and less tightly packed structures, leading to lower densities. In contrast, alkaline earth metals, with their additional electron, have more compact atomic structures and are generally denser.

Alkali Metals

Alkali metals belong to Group 1 of the periodic table. They include elements like lithium (Li), sodium (Na), and potassium (K).

• These metals are characterized by having a single, loosely bound electron in their outermost shell.
• This sparse electron structure makes their atoms less tightly packed, resulting in lower density.
• Alkali metals are also highly reactive due to their tendency to easily lose that outer electron.

The lower density of alkali metals is due to their atomic structure, where the single outer electron does not contribute significantly to tight atomic packing.

Alkaline Earth Metals

Alkaline earth metals are found in Group 2 of the periodic table, including elements such as magnesium (Mg), calcium (Ca), and barium (Ba).

• These metals have two electrons in their outermost shell.
• This configuration leads to a more compact and orderly atomic packing.
• The presence of the second electron results in greater atomic bonding and, consequently, higher density.

Alkaline earth metals are not as reactive as alkali metals but still exhibit significant reactivity. Their increased density is a direct result of their more compact atomic structure, where the additional electron helps in tighter atomic bonding.