Magnesium (Mg) reacts with chlorine \(\left(\mathrm{Cl}_{2}\right)\) to form the compound \(\mathrm{MgCl}_{2}\). (a) Predict the formulas for the compounds formed when all the other alkaline earth metals react with chlorine. (b) Predict the formulas for the compounds formed when all the alkaline earth metals react with bromine. (c) Explain what principle you used to make your predictions.

To predict the formulas for the compounds formed when all other alkaline earth metals react with chlorine, we need to know the valence electrons of both these metals and chlorine. Alkaline earth metals are found in group 2 of the periodic table, and therefore have 2 valence electrons. Chlorine, in group 17, has 7 valence electrons. According to the octet rule, the alkaline earth metals will lose their 2 valence electrons and the chlorine will gain 1 electron to complete its octet. This means that 1 alkaline earth metal atom will form a bond with 2 chlorine atoms, resulting in compounds with a 1:2 ratio of metal to chlorine. So, the formulas for these compounds are: - BeCl₂ (Beryllium chloride) - CaCl₂ (Calcium chloride) - SrCl₂ (Strontium chloride) - BaCl₂ (Barium chloride)

Similar to part (a), we need to know the valence electrons for both the alkaline earth metals and bromine. Bromine is also in group 17, one element below chlorine, and therefore has 7 valence electrons. Using the octet rule, 1 alkaline earth metal atom will form a bond with 2 bromine atoms, resulting in compounds with a 1:2 ratio of metal to bromine. So, the formulas for these compounds are: - BeBr₂ (Beryllium bromide) - MgBr₂ (Magnesium bromide) - CaBr₂ (Calcium bromide) - SrBr₂ (Strontium bromide) - BaBr₂ (Barium bromide)

The principle used to make the predictions in this exercise is the octet rule. The octet rule states that atoms tend to combine in such a way that they each have eight valence electrons, giving them the same electronic configuration as a noble gas. In this case, the alkaline earth metals lose their 2 valence electrons, and the non-metal atoms (chlorine or bromine) gain 1 or more electrons to complete their octet, forming ionic compounds with a 1:2 ratio. This principle allows us to predict the formulas for the compounds formed when alkaline earth metals react with both chlorine and bromine.