Final answer:
The smallest alkaline earth element is beryllium (Be), and it is less common compared to other alkaline earth elements.
Step-by-step explanation:
The smallest alkaline earth element is beryllium (Be). Beryllium has an atomic number of 4, meaning it has 4 protons in the nucleus. It also has 4 electrons surrounding the nucleus, with the fourth electron filling the remaining space in the 2s orbital.
In terms of abundance, beryllium, as well as strontium and barium, are considered rare among the alkaline earth metals. On the other hand, calcium and magnesium are the fifth and sixth most abundant elements on Earth, respectively, and are found in significant deposits of limestone and other minerals.