Final answer:
An alkali metal combined with chloride forms a compound with the formula MCl, whereas an alkaline earth metal combined with chloride forms a compound with the formula MCl2.
Step-by-step explanation:
To write a compound formula for an alkali metal combined with chloride, we must consider that alkali metals (found in Group 1 of the periodic table) have a +1 charge. Chloride ions, being derived from chlorine, have a -1 charge. Therefore, for any alkali metal (M), the compound formula with chloride would simply be MCl. For instance, if we choose sodium (Na) as the alkali metal, the compound formula would be NaCl.
When combining an alkaline earth metal with chloride, it is important to note that these metals (found in Group 2 of the periodic table) have a +2 charge. Chloride ions have a -1 charge. In order to achieve electric neutrality in the compound, two chloride ions are required to balance one alkaline earth metal ion. So the general formula would be MCl2. An example would be combining calcium (Ca) with chloride to form calcium chloride, with the formula CaCl2.