Provide the following:
c. the atomic mass and symbol of the alkaline earth metal in Period 3
d. the atomic mass and symbol of the halogen with the fewest electrons

Alkaline earth metals are a group of elements found in Group 2 of the periodic table. They are characterized by having two electrons in their outermost shell, which makes them highly reactive, though less so than alkali metals. In Period 3, the alkaline earth metal is magnesium (Mg), which has an atomic mass of approximately 24.31 u.

Halogens are elements found in Group 17 of the periodic table, known for their high reactivity due to having seven electrons in their outer shell. The halogen with the fewest electrons is astatine (At), which has an atomic number of 85 and an atomic mass of about 210 u. Halogens typically form salts when they react with metals.

The periodic table is a systematic arrangement of elements based on their atomic number, electron configuration, and recurring chemical properties. It is organized into periods (horizontal rows) and groups (vertical columns), which helps predict the behavior of elements. Understanding the layout of the periodic table is essential for identifying elements and their properties, such as atomic mass and reactivity.