Question

predict the formula of the compound formed between calcium and bromine

Answer 1

Calcium (Ca) has atomic number 20 and it lies in group 2 (alkaline earth metals) of periodic table which means it has 2 valence electrons. Its electronic configuration is ​​​​​​. Its valency is 2 because it can lose 2 electrons to get stable electronic configuration of Argon (Are). So it will form cation Ca²⁺.Bromine (Br) has atomic number 35 and it lies in group 7(halogens) of periodic table which means it has 7 valence electrons. Its electronic configuration is . Its valency is 1 as it can gain 1 electron to get stable electronic configuration of Krypton (Kr) . So it will form anion Br^-​​​​. Now to form a compound between Ca and Br, the charges on the ions need to be balanced. So 2 Br^{​​​​​-} ions are needed to balance the charge on Ca^{​​​​​2+}. Also we write the symbol of metal first and then the non-metal. The charges are not mentioned in the formula. So the formula of the compound will be CaBr₂.