Why do beryllium and fluorine combine in a 1 : 2 Ratio?

Be is in group 2 (or IIA). F is in group VIIA (or 17 depending upon what system you are using). Therefore, flourine needs one electron to fill its outside shell. Be has two in its outside shell to give. So Be gives an electron to each of two F atoms to make BeF2.

why do beryllium and fluorine combine in a 1:2 ratio?

Beryllium and fluorine combine in a 1:2 ratio because of their electron configurations and the octet rule. Beryllium, which is in group 2 of the periodic table, has 2 electrons in its outermost shell. On the other hand, fluorine, which is in group 7, requires 1 more electron to complete its outer shell and achieve stability.

In order for beryllium to achieve a stable electron configuration, it can donate its two outer electrons to fluorine atoms. Each fluorine atom can accept one electron, as it only needs one more electron to fill its outer shell. Therefore, one beryllium atom can donate two electrons to two fluorine atoms, resulting in a 1:2 ratio of beryllium to fluorine.

This electron transfer allows both atoms to attain a more stable electron configuration. Beryllium loses its two outer electrons and becomes positively charged, forming Be2+ ions. Fluorine gains one electron from each beryllium atom and becomes negatively charged, forming F- ions. These ions then attract each other due to their opposite charges, resulting in the formation of ionic bonds and the compound beryllium fluoride (BeF2).