Atomic Radius Order of B, Be, Al, and Mg

Introduction:
The atomic radius is defined as the distance between the nucleus of an atom and the outermost shell of electrons. It determines the size of an atom and plays a crucial role in various chemical and physical properties. In this response, we will arrange the elements B (boron), Be (beryllium), Al (aluminum), and Mg (magnesium) in atomic radius order.

Explanation:

Boron (B):
- Atomic number: 5
- Electronic configuration: 1s² 2s² 2p¹
- Boron has a smaller atomic radius compared to the other elements in the list.
- This is because boron has a higher effective nuclear charge, which attracts the electrons closer to the nucleus, resulting in a smaller atomic radius.
- The presence of only one electron in the 2p orbital of boron leads to less electron-electron repulsion, further reducing the atomic radius.

Beryllium (Be):
- Atomic number: 4
- Electronic configuration: 1s² 2s²
- Beryllium has a smaller atomic radius than both aluminum and magnesium but larger than boron.
- The 2s orbital of beryllium is closer to the nucleus compared to the 2p orbital of boron, leading to a smaller atomic radius.
- Beryllium also has a higher effective nuclear charge than boron due to its additional protons, further decreasing the atomic radius.

Aluminum (Al):
- Atomic number: 13
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p¹
- Aluminum has a larger atomic radius compared to both boron and beryllium.
- This is because aluminum has additional electron shells, resulting in an increase in atomic size.
- The screening effect of the inner shells also reduces the effective nuclear charge experienced by the outermost electrons, contributing to a larger atomic radius.

Magnesium (Mg):
- Atomic number: 12
- Electronic configuration: 1s² 2s² 2p⁶ 3s²
- Magnesium has the largest atomic radius among the elements in the list.
- It has more electron shells compared to boron, beryllium, and aluminum, which increases its atomic size.
- Additionally, the screening effect of the inner shells reduces the effective nuclear charge, further expanding the atomic radius.

Atomic Radius Order:
Based on the above explanations, the elements can be arranged in increasing order of atomic radius as follows:

B < be="" />< al="" />< />

Conclusion:
In conclusion, the atomic radius order of the given elements B, Be, Al, and Mg is B < be="" />< al="" />< mg.="" this="" order="" is="" determined="" by="" the="" effective="" nuclear="" charge,="" electron-electron="" repulsion,="" and="" the="" number="" of="" electron="" shells.="" boron="" has="" the="" smallest="" atomic="" radius="" due="" to="" its="" higher="" effective="" nuclear="" charge="" and="" fewer="" electron="" shells.="" beryllium="" has="" a="" slightly="" larger="" atomic="" radius="" than="" boron="" due="" to="" its="" additional="" electron="" shell.="" aluminum="" has="" a="" larger="" atomic="" radius="" than="" both="" boron="" and="" beryllium="" due="" to="" the="" presence="" of="" additional="" electron="" shells.="" finally,="" magnesium="" has="" mg.="" this="" order="" is="" determined="" by="" the="" effective="" nuclear="" charge,="" electron-electron="" repulsion,="" and="" the="" number="" of="" electron="" shells.="" boron="" has="" the="" smallest="" atomic="" radius="" due="" to="" its="" higher="" effective="" nuclear="" charge="" and="" fewer="" electron="" shells.="" beryllium="" has="" a="" slightly="" larger="" atomic="" radius="" than="" boron="" due="" to="" its="" additional="" electron="" shell.="" aluminum="" has="" a="" larger="" atomic="" radius="" than="" both="" boron="" and="" beryllium="" due="" to="" the="" presence="" of="" additional="" electron="" shells.="" finally,="" magnesium="" />

Mg>Al>Be>B